Electronic welding machine in short circuit - Page 1
Forum section: electronics / beginners

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 21, 2024, 06:27:01 am
content: Hi, I have an electronic welder that no longer works. It turns on regularly, the green light works and so does the fan, but I have no voltage on the output. It should have about 80 volts at no load. Visually I don't notice any burnt components, but when I power the board via variac and a light bulb in series, there are moments in which I feel the fan speed drop and the light bulb lights up slightly, indicating that there is a short circuit on the board. I checked the temperature of the components, but I can't find anything with high temperatures. Do you have any advice for finding the short circuit? The card is very similar to this one, thanks.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 21, 2024, 06:32:53 am
content: I add the electrical board diagram (not 100% identical, but almost the same)

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 21, 2024, 06:37:56 am
content: Maybe you can see it better in the PDF (it's from an inverter of the same brand, but I'd say that the PCB is almost identical)

author: coppercone2
author_rank: Super Contributor
timestamp: July 21, 2024, 07:01:45 am
content: its something on a heat sink if you cant find it

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 21, 2024, 10:21:16 am
content: The bulb dissipates the short circuit, so no protection fails and perhaps not even the faulty component. There are many heat sinks, is there a way to understand if it really depends on a heat sink? The board also has thermal control, but I believe only on one of the two heatsinks with 4 IGBTs. Thank you

author: coppercone2
author_rank: Super Contributor
timestamp: July 21, 2024, 10:23:19 am
content: Ok I am saying if you think there is a short circuit, but you can't find any hot parts, chances are its a part on a heat sink, or with a heavy ground plane.For high voltage power boards you really want a thermal camera that can point you in the right direction. Usually bad welding machines have blown parts.My broke welder had clear signs of burn damage. Did you check perhaps to inspect the parts with a mirror to look for a cracked transistor? They often blow a corner off or something like that and look mostly OKThis one looks really simple. You could replace every single part fairly cheap, its always an optionMy hunch is something bad with parallel MOSFET. I would just buy a dozen on digikey and give it a shot replacing them all lol, for 20$ + thermal grease. Chances are it might be a cheap welder with counterfeit parts (suspicious this is from amazon) and you might improve the thing. Plus, its kinda safer then probing around those. And you can probe most of the diodes too.With parallel mosfet it might be complicated to try to determine if one of em is acting up, their like $2.95 so is it worth it ?A good machine would have factory made IGBT bricks for this purpose. Parallel FET is alot cheaper but yeah who knows what can happen there!I can ensure you, that probing those FET near the heat sink while its running is perilous. If you wanna try to do something there, get a fluke insulated grabber hook, turn off the machine, make sure its safe, connect the hook, measure, and repeat for every single measurement. Probing there while its on is the risky part for this machine. Those TO packages near BIG heat sinks are recipe for short circuit trouble

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 21, 2024, 11:11:55 am
content: Quote from: coppercone2 on July 21, 2024, 10:23:19 amThanks, it's very kind of you. I'm at work, tonight I'll reflect on your advice

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 04:56:55 am
content: My experience troubleshooting an inverter electronic welding machine board is that of a beginner.There are few transistors, they don't seem to be shorted, but they should be desoldered for an accurate check. Then there are some power diodes (they seem ok) and 8 IGBT (soldered onto the circuit, it is difficult to verify if they are efficient).Of course I could replace the power components, but first I wanted to understand where the short circuit was located; It's not easy because for many minutes it doesn't absorb any extra current, and when it happens the bulb disperses it without causing further damage.In reality the welding machine is not a super cheap model, even if it is many years old, but it has not worked much. The model is EPS energi@130 (manufacturing company is eps-inverter.com).When it was given to me as a gift, the electrode only produced a few sparks, in fact the output is zero volts (it should be 80 DC at no load).I carried out the voltage check on the component side only with the probe cable that detects the temperature, while I carry out the measurements on the track side.For now I have verified that on the large filter capacitors I regularly have 310 DC; the relay works; the fan works. On the gate of 4 mosfets I have a voltage, while at the moment I don't have any voltage on the gate of the other 4 mosfets, but I have to check better. The IGTBs are IRF P 460s.I add some photos: secondary diode

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 05:02:34 am
content: transformer area

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 05:04:21 am
content: 8 IGBT

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 05:05:49 am
content: hybrid logic board (covered by a transparent protection)

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 05:07:48 am
content: Track side (I scratched the transparent protection, otherwise it wouldn't conduct on the multimeter tip)Note the fixing of the 3 large heat sinks, with rivets...

author: odemiriz
author_rank: Newbie
timestamp: July 22, 2024, 07:31:13 am
content: If the welder powers on regularly (meaning green led on and no error led), primary switches - mosfets or IGBTs - are fine. You should first check output diodes with a multimeter. If there is a short there, you need to change the faulty ones. If not most likely you have problem with control board. Check the aux power for the control section.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 10:50:43 am
content: Quote from: odemiriz on July 22, 2024, 07:31:13 amYes, the welder turns on regularly, the fan turns and the green light is on; the yellow light does not come on (not even when the bulb indicates a slight short circuit). The output diodes (BYV52) verified in the diode test (on the board), would appear to be ok. I haven't yet done accurate voltage and signal tests in the control part, on the gate of 4 mosfets I have a voltage, while on the other 4 gates I have a zero voltage, but from the diagram it seems to me that it refers to the ground so maybe ok. The resistors and diodes between T4 and the gate seem ok. I don't understand what it is that doesn't allow the current to reach the output.When the light bulb signals me the short circuit (only occasionally while the welder is running idle), I then lower the variac below 200AC and the short circuit disappears. I almost want to let him continue to see if he smokes anything, but I don't want to do any more damage. I still have to check better, but I had the feeling that by leaving the current regulator towards the minimum, the short circuit is more frequent, while if I raise the potentiometer towards the maximum (130 A), it doesn't signal any short circuit, but I have to do further tests . However, the output always remains at zero DC.Thank you

author: coppercone2
author_rank: Super Contributor
timestamp: July 22, 2024, 11:56:42 am
content: well if the current is not reaching output that means the bridge is stuck or fried or control is fried. is the control card making a wave form into the gate of the transistors?

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 22, 2024, 02:30:16 pm
content: Quote from: coppercone2 on July 22, 2024, 11:56:42 amI think it's quite difficult for me to understand this fault. I have attached part of the diagram where I took some measurements. In the moments WITHOUT a short circuit, at the input of TR4 I have the right voltage (13.7v); at the output I have about 18/20v, which arrive at the gates of MF1-2-3-4. On the other output of TR4 I have the ground reference, which continued up to the gate of MF5-6-7-8.During short moments, the output voltage from TR4 to MF1-2-3-4 alternates from 20 to 120 v!, and the input of TR4 drops from approximately 13.7 to 10 v. I also saw that the yellow LED lights up in moments of short circuit.In the diagram I see that they distinguish between two types of mass (one has the symbol F). However, I see that there is continuity between these two masses on the PCB.Thank you

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 23, 2024, 06:48:24 pm
content: I'm checking all the components one by one, for now I've reached after the large capacitors and everything seems ok (in moments of short circuit they drop from 310 to 200 DC, but I think it's normal, I also have the lamp in series).When I get to the power components (mosfets, diodes, transistors, voltage regulator), I will disassemble them from the board including heatsinks, for better control.For each component that I desolder, I will test the board under voltage to see if the occasional short circuit will disappear, in this way I should limit where the problem lies.Some doubts:-I didn't understand why they fixed the large heat sinks with copper rivets, in this way, for example, the leveled voltage of 310DC that reaches the drain of 4 mosfets, we also have it on the entire heat sink (I don't understand this choice).-I read that desoldering/soldering the mosfets could ruin them, are perhaps precautions needed in this regard? Is the classic CPU thermal paste used between the heat sinks and the MOSFET body?-the only components that I hope do not have problems are the two chips on the hybrid board (Lm324 and TDA1060), I will have to find a way to verify their integrity carefully before changing the other components of the board...

author: coppercone2
author_rank: Super Contributor
timestamp: July 23, 2024, 08:50:17 pm
content: yeah it might be risky to remove all those MOSFET if you plan on reusing them.The keys are1) esd protection2) thermal protection for the chip. You can use a heat sink clip from gootwick, which is a aluminum solid alligator clip that does not stick to solder and prevents heat from going into the part.. their very useful for repairs IMOI don't know how to test MOSFET good for the conditions they are in in the welder though. I think there still might be problems even if a simple test says its OK, like switching speed or something causing something. I think you need a fairly elaborate test fixture to really 'test' a power MOSFET for complex tasks other then switching on a heater you know?I think you should try to map the signals out though, before you desolder heavy parts. It should be getting a oscillator waveform of some kind to trigger the transistors. You need to find it on a scope IMOThe gate driver circuit and the gate driver control circuit can be evaluated with a oscilloscope. The gate driver control circuit is some kind of oscillator that makes a low power signal square or other wave form. The gate driver is a pulse amplifier circuit that allows the little control signal to drive the big transistors fast enough. More then likely its a PWM type signal with A and Abar phases to control the bridge.Just to give you an irrelvant annecdote:my welding machine had a ton of problems like exploding diodes (miller dynasty 200). Some how Eventually I found a leaky ceramic capacitor like 7 inches away. The problem stopped when I replaced it. This leaky capacitor was causing all sorts of trouble, but their circuit is rather complicated compared to this one. And yes, I did replace ALL the power parts in it, and it was still doing the same thing. So be careful, I am pretty enthusiastic about replacing power parts, but its NOT a cure all. It is possible some little piece of crap part is making it go hay wire and that all the big parts are OK.

author: coppercone2
author_rank: Super Contributor
timestamp: July 23, 2024, 08:58:38 pm
content: Do you have a control signal on M_13 and M_14 on your diagram coming out of the board? That is the start of it. Then the transformer in this case is like a BALUN?, which makes the signal differential (A and A_ ) to drive the H bridge.If one of those 4.7 Ohm resistors is off, it could mean a bad FET. Those resistors are power resistors. I think D1 is a clamp, and T2 and T3 is your gate drive amplifier. The part there is a power amplifier D45H8DZ1 is limiting the voltage to 18V, the FET probobly does not like more then 20V on the gate.The thing I am confused about is the D45H8... because every H-bridge I worked on, it has a power source there, it looks like that chip is just floating. The MOSFET are fairly beefy and they take alot of current to turn on and off. I am not getting this part since its connected through a transformer only. My miller had isolated 20V rails to power the driver, like an auxillary IGBT gate drive power source. The gate drive then get a signal from a MCU that it amplified to control the transistors.I think you need someone with a little more knowledge of this circuit then me.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 23, 2024, 10:23:20 pm
content: Quote from: coppercone2 on July 23, 2024, 08:58:38 pmYou also do too much Coppercone, thank you for your availability; in the next few days (I'm away for work now) I will continue the research, also taking advantage of your precious advice. If anyone else wants to help me, I will be grateful. Unfortunately I have never studied this kind of circuit (inverter), I'm doing it now step by step, I started from the side with mains voltage and will continue until the output.I would add that it is not easy not having the precise diagram, the one in the pdf is very similar (same brand but not identical, even if in the first part of mains voltage, it is practically identical except for R39 which is not there in mine).If the problem is not on the vertically soldered logic board (I attached the photo previously), I think I will be able to analyze the components one by one even by removing them from the board. As long as the problem is not on the LM324 IC which would not be easy to replace, both due to the wax they put on the PCB and the very close contacts.In the meantime, thanks, I'll let you know the progress (or even failures)

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 24, 2024, 04:49:05 pm
content: Meanwhile, I only analyzed the part of the Tr4: 13.7v arrives at the central pin of the Tr4 (from the regulator IC1, Lm317), the other two pins (which arrive from M13 and M14 of the hybrid board, have the same potential (if I look the signals on these 3 pins, referred to ground, are 13.7 DC). The low output of Tr4 (the one towards the MF5-8 mosfets), has zero volts a sinusoidal signal, but at this moment the light bulb indicated a slight continuous short circuit, so the signal was very dirty (it increases by many volts, the regulator Ic1 does its job, coming out at 13.7). that on the 3 input pins of Tr4 I have continuity, as on M13 and M14 (after all they all have 13.7v).In the meantime I'll take one step at a time and as you advised me I won't desolder the mosfets. If you could find where the short is coming from, but apparently it doesn't heat anything abnormally. I also found two schematics on the 15 pin hybrid board, not exactly the same layout, but close enough, I'll attach them.Thank you

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 24, 2024, 07:30:20 pm
content: Quote from: coppercone2 on July 23, 2024, 08:50:17 pmAs recommended, I will first map all the components, trying to understand without desoldering them which ones are ok and which ones could have problems. If the problem lies in a leaking cap, I would find it, as I desolder those and check them on the component tester. My fear is that there is some transformer with problems, there are 4 of them. For now I have only found the R 10 (output area) of suspicion, I have not desoldered it but it gives a low resistance, instead of 3, 9K, but I don't think that's the source of the problem. Thank you

author: coppercone2
author_rank: Super Contributor
timestamp: July 24, 2024, 08:29:59 pm
content: A ceramic hybrid card is a pretty good heat sink. Its possible there is some power being dissipated there that is difficult to trace.For heat sinks, if you glue thermocouples on them, and run it for a while, while the difference is small, your meter can even resolve 0.5 degrees normally. It might seem abnormal. But if you just press a thermocouple into it, it might not be stable enough of a measurement to find a small difference. Clipping it on with a alligator clip that has rubber on it might work without glue for a heat sinkand I never tried this one before, but I did get a interesting idea : what if you insulate the heat sinks with some cloth strips or something, to contain heat, or plug the fins. Then it might start showing up. If the heatsink is effectively isolated, it just a thermal reservoir. Eventually it will heat up from even a minor short. But its mechanically complicated. I imagined wrapping it up like a mummy with wool strips.. just have the fire extinguisher handy and dont leave it unattended LOL. I think it would work to increase the 'resolution' but its going to be hard to apply for some designs.

author: coppercone2
author_rank: Super Contributor
timestamp: July 24, 2024, 08:47:49 pm
content: and another place you can have a nasty semi short is under power connector plastic. Its a heavy power/ground plane, if you have corrosion or whatever there, it could be getting hot UNDER the plastic, not hot enough to melt it, and going right into the ground plane.I am sure you noticed how hard it is to desolder those power planes, aka they can sink ALOT of watts before things get interesting.I.e. I saw this with a sorensen 30A supply. The main input connector terminal block (3 screw) was soldered to the PCB. They did not put enough solder into one of the holes, so over time it cracked and kinda wiggled and sparked. In my case it went open circuit after some bad sparking, but there was soot present. If more soot accumulated there, under the plastic connector, I could see it POSSIBLY forming a parasitic resistor of sorts, which would be well heat sinked by the huge power pins and the power planes and hidden by the connector body.Sometimes I really miss the 1960's style design, where all the power pins had no insulators, so if there is anything going on, you can see right down to the board. When you start having plastic connector housings, you can hide things under the housing, and its damn near impossible to find unless you remove the connector ! Corrosion goes there too, if there is batteries around. The battery juice wicks up the wire and ends up depositing in/under/around the connector. Mad hard to clean unless you disassemble and scrub wash everything.

author: coppercone2
author_rank: Super Contributor
timestamp: July 24, 2024, 08:55:50 pm
content: And another possibility that I have never seen before is with the heat sink itself.Usually the heat sink is built so it has small stand offs, or they can put washers to lift it off the board, which might have traces running under neath. But, its always possible, especially when its not designed into the heat sink, that you can have a heat sink that is flush pressed against the PCB. If you have traces running there, then its possible for it to over time work its way through the solder mask and start messing shit up. Like if they forgot to put some washers in during assembly and just soldered it up flush on the PCB.I don't work on power boards much, so I don't know how prevelant it is to have traces running under a heat sink.Also sometimes boards warp ALOT more then engineers think, so its possible that something like a elevated heat sink is shorting out a bowed circuit board. For design, I would recommend putting some kind of separator under heat sinks that have traces under them, like fish paper, teflon, kapton, etc. And you can have scenarios where there is a chassis screw on the other side of the board... if someone installs the wrong screw, it can jack up the board and bend it to cause some kinda short.Some of my older PCB I have look like airplane wings when I take them out of the chassis lol, they bend like 1/2 a cm. It can be from age or just from soldering, if its layed out with thermal imbalance, heated too much... but usually because its pressed into a chassis that might get dented or something and slowly "form" the PCB into some pringle shape... I think it might even be possible for a PCB to bend while its in use from the heat that its making, and then go back, like a bimetalic stripI really recommend getting a thermal camera for this job though... their game changers for repairs. you get SO MUCH INFO with so little effort.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 24, 2024, 09:37:28 pm
content: Thanks Coppercone, your ideas are always very interesting, I like it when you remember the repairs of your past time. I'm at work and I can't verify anything now, but the power supply is direct to 2 exposed fastons (plus earth), there is no plastic connector; the black plastic that can be seen is only a thickness that raises the card from the chassis, but does not cover the connectors. While the large heatsinks if I remember correctly have a black gasket between them and the board. I think you read my thoughts, I'm going on holiday in the next few days and therefore I will have more time to dedicate to this repair and I have already put the thermal imaging camera on the list, which as you rightly said could help a lot in the search for short circuits. Nothing professional, I saw on Aliexp... a couple of thermal cameras for around 140-180 euro, they could also be fine for a beginner like me (I have also seen 10 IGBT MOSFET like those on the card for 5 euro, but for now I wouldn't change them). Thanks again for the valuable suggestions.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 29, 2024, 11:29:54 am
content: I am calmly checking the entire diagram at my disposal (same manufacturer, but slightly different inverter), correcting the wrong parts. I started from the top and now I am about 1/3. I found only a few components with incorrect values, which I will then unsolder for a better check, but nothing short-circuited.The last check I did was on the potentiometer area (M7 of the hybrid board, PT1 and Rv32): the potentiometer is 4.7K, but on the two side pins the resistance is 2.6K (I did not unsolder it, but in this case I think it is not necessary); Rv32 should be 2.7K and instead it is 1.9K (I will change it). The research continues.Edit: Rv32, in my circuit it is a normal resistor (not adjustable)I report again the diagnosis of the welder: it turns on regularly, green LED ok, the fan works, but occasionally it has a slight short circuit (light bulb in series turns on) that lasts maybe a few minutes then disappears; sometimes together with the short circuit the yellow LED also turns on, but not always. I have no output voltage (idle I should have about 80v)I attach the diagram, it is correct from the top up to about M7 (below still to be verified)

author: coppercone2
author_rank: Super Contributor
timestamp: July 29, 2024, 10:42:25 pm
content: hmm well you know my miller dynasty works fine but it sounds like its sometimes changing its loud ass whine like the circuit is doing something. It must be using a fair bit of power doing whatever its doing when its doing nothing to change the acoustic tone that much.The only thing I thought of is maybe the PFC. Could the PFC not be drawing some more current to fix up BS on the input to keep it running smooth? I figured the PFC is the cause of the odd behavior I see with my welder. The PFC has to deal with anything strange the line is doing by any means possible. I imagine PFC circuits have inconsistent power draw, they need to respond heavily to fix mains? But I don't know much about them.I meant to run my machine off a battery inverter that should have a different stability then mains to see if it sounded more consistent, but I never bothered because its hooking 2 inverters that are complicated and it kinda scared me. However one day I might turn it on while I am on generator power if I remember to see what happens.I don't know what other component would be randomly changing the load on different inductors and capacitors at idle other then the PFC. In one sense, you can think of the PFC as something that shorts out the line... its how its drawn.My brand new inverter air conditioner seems to make similar weird whines and such to the miller dynasty, so im not terribly worried about the noise, I figure it kind of goes with the territory of high power line inverter. Its a bit unusually loud for a no load welder but I am not expecting miracles from a beast like that lol, there had to have been compromises made in that design... however my hypertherm plasma cutter is very quiet when its doing nothing. But miller noise complaints seem common.Anyway, I assume that if I put a bulb on there, it would also be drawing irregular amounts of intermittant energy. oddly enough it seems correlated to the display. I could not figure it out, and the less that thing is probed the better, I would rather have that machine fail then get between that thing and the ground. If it goes with the chassis cover attached, its just a financial problem lol... the skill of being able to actually use the tig torch is infinitely more valuable then having the tig machine working... its only like 3 months of savings even on a low salary.... figure if that happens your eyes can regrow some cells while you save

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 30, 2024, 06:54:55 am
content: Thanks Coppercone, you are always very kind and have interesting ideas. I don't know how this inverter welder worked before. The person who scrapped it (gave it to me) only said that it always worked, then one day he decided to use larger electrodes than usual (about 3 mm) to make large welds (according to the specifications this welder could use them, but perhaps without exaggerating), and it did its job, but later when it was used again it welded half an electrode and then only small sparks (after all I don't have DC in output). You think that I have another inverter welder (Telwin 144, this brand is also Italian, quite widespread here) that works well, but as a scheme it is slightly different from this EPS, and it doesn't make any noise when it is without load, I simply have about 75 DC in output. As I said, for me it is the first time that I analyze a circuit of this kind (inverter), I am doing it calmly analyzing piece by piece. Even if I won't be able to repair the machine, it will all be educational baggage. Today I should receive a thermal camera (a cheap Chinese one), we'll see if it will show me some hot parts. Even if the short circuit is unfortunately only occasional and not devastating (the light bulb lights up sometimes, but not much). Watching various repair videos on welding machines, I saw that often the faults were on the secondary output diodes (here we have 4 on a large heatsink), but from the diode test they all seem ok (I haven't unsoldered them yet though), but I don't think they are the problem. I haven't yet got to analyze the small hybrid analog control board, where I will have to understand if the two integrated circuits work correctly (there is an LM324 and a TDA1060). Thanks

author: coppercone2
author_rank: Super Contributor
timestamp: July 30, 2024, 07:16:04 am
content: another shot in the dark : intermittent power draw can be like minor arcing ? A spark gap has this behavior, voltage rises and it sparks. Maybe there is a capacitor and resistor that is making mild sparks some where inside?

author: coppercone2
author_rank: Super Contributor
timestamp: July 30, 2024, 07:19:56 am
content: Can you find any correlation...if the light bulb is lighting, maybe a voltage rail is shorting partially, then maybe you would see a voltage drop some where, maybe. even a few volts. if you can correlate it.

author: DisasterNow
author_rank: Regular Contributor
timestamp: July 30, 2024, 10:51:49 am
content: I power the board with the variac starting from zero up to 220Vac, sometimes for many minutes no absorption on the bulb in series, sometimes instead it starts, lasts maybe a few minutes and then the short seems to disappear (to then return later ...). No smoke or smell of burning, nothing. However I have not checked the sparks, I should try in a dark room, having only the little light on the bulb that signals the short. I will try, even if in any case if I had belts maybe I would smell a slight smell of burning. Needless to say, even when it does not signal any short, the fan runs and the green LED is on normally, but on the output I have no voltage. When the bulb signals the short, the signals widen fearfully on the display (for example the 13.7DC amplifies for tens of volts), the voltage on the part of the large capacitors drops even by 100v, while on the 13.7 volt towards the IGBTs I even have 120v ... In short there is instability everywhere. Now I will continue to check every component not yet checked, I will check with the thermal camera for any heating. I also thought about interrupting some tracks to better isolate where the short came from. I will try to proceed calmly. Thanks

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 12:19:58 pm
content: Quote from: coppercone2 on July 23, 2024, 08:58:38 pmI quote this message from Coppercone again.Below I report the part of the diagram that I have not yet analyzed, as I am having trouble understanding how the current is triggered towards the output.I have checked all the other inputs/outputs of the LDC1002 hybrid board and there do not seem to be any problems, I only have the M13 and M14 pins left (the most important...).I am confused about what happens in sequence on the 3 transformers (TR4, TA1, TR2), starting from TR4 where I see a primary on the M13 and M14 contacts of the control board, but I also see a central tap where the 13.7DC arrive, then it has the two secondaries in phase, one towards the positive part of the H-bridge and one towards the negative. If I measure on the 3 pins of the primary side of this Tr4, I have 13.7DC on all 3. I do not understand if it is ok.The 8 resistors before the gates of the 8 IGBTs are all ok (4.7 ohms).In short, I am lost in this part of the circuit where I have these 3 transformers, I do not understand how they interact with each other (the part above that I do not report here I have analyzed it all and it seems quite ok). Below I will report the diagram of the part that I do not understand and some significant images. If anyone has any advice on what to analyze, I would be very grateful. Thanks

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 12:20:50 pm
content: set of components

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 12:21:37 pm
content: image of the 4 transformers (I have already analyzed TR3, it is used to have +13.7DC and it seems ok)

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 05:27:29 pm
content: Here is the sketch I found online of the LDC1002 control board (very similar, but mine is missing some components due to the manufacturer's choice). I highlighted the part of the M13 and M14 pins

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 05:28:12 pm
content: This is the sketch (always from the net) of the connections on the inverter board to the pins of the control board (you can clearly see the circuit of M13 and M14 towards TR4, where the 13.7DC voltage also arrives). R10 is not present on my control board, empty pad.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 01, 2024, 05:29:49 pm
content: And here are the components on the hybrid board that concern the M13 and M14 pins (D5 with diode test detects voltage from both directions, but I did not unsolder it for an accurate test).

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 02, 2024, 03:55:27 pm
content: My personal and solitary battle with this inverter welder continues.I checked the area of ​​pins M13 and M14 of the hybrid board, from here the tracks go to the TR4 transformer (and subsequently to the gates of the Mosfets): the signal that should arrive at M14 should originate from pin 14 QE of the TDA1060 chip and then pass into the IRF110 Fet. The TDA1060 is regularly powered at its pin 1 with 13.7v and I see that for example on pin 2 it regularly supplies a stabilized voltage of 8.4v. But from pin 14 QE no signal comes out (zero voltage) which according to the diagram would then arrive at the gate of the IRF110 fet. So on the contacts that arrive at TR4 I only have a DC of 13.7 which as you can see powers the same primary of TR4.Now I would like to understand if it is the internal part of the TDA1060 that is faulty and does not send the signal to its pin 14 QE, or if instead the TDA1060 is in protection for some other problem elsewhere. Here is the sketch of this part of the circuit (in the other message I add the TDA1060 schematic and the notes on the QE output).Correction: in my sketch, the top/right pin of the IRF110 is the gate (and not source)

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 02, 2024, 03:57:33 pm
content: Datasheet TDA1060Output QC and QE (pins 13 and 14):To avoid double pulses that might occur at an excessively low mains voltage or an excessively high output current the output is preceded by a latch. The two outputs offer a choice of output current polarity, QC giving a positive current, i.e. a current flowing into the output, and QE giving a negative current, a current flowing out of the output. The two connections have the additional advantage that the relatively large output currents do not flow through the Vcc and VEE connections, where they could induce noise.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 21, 2024, 04:11:48 pm
content: Following the board, I was able to get the exact circuit diagram (the generic one I had was different in many parts). I then checked it with the thermal camera to understand where the short circuit is hidden (I always do the tests with a light bulb in series, so some temperatures are also optimistic ...).The only points hotter than the others when there is no short circuit are only these:R3, 65°: is it the 220K resistor that is after the two large smoothing capacitors (on the 310DC), perhaps it dissipates the excess current to ground?RL1 (relè), 60°IC1 LM317T, about 70°: generates the stabilized voltage at 13.7 (the P2 bridge also seems warm, but I think it's normal...).R16 e R17, 52°: they listen to the +V voltage (310DC), and in series they indicate a voltage to the logic (which is ok anyway, 6.5Dc).R15, 69°: It's the resistance of the green LED of the welder, strange that it heats up so much.No other parts seem hot.When I then have some signs of a short circuit (I see it from the light bulb in series), I saw that the only parts that heat up are C11 (but not excessively), and especially R11 which reaches even 145° (R11 is ok, I also replaced it).So the short circuit current passes through R11, which is almost in the output part of the circuit (before the secondary diodes).When there is no short circuit, both R11 and C11 are at 30°.However, I can't find where the short circuit comes from, and obviously at the output of the board I have no voltage (I should have more than 60DC).If anyone has any suggestions on some further checks, welcome. Thanks.I attach the final diagram of this electronic welder (I circled in red the only two components that I see heating up when I have a short circuit).

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 12:32:27 am
content: The resistors after smoothing capacitors are always hot, they need to drain them fast ,it uses alot of energy and gets hot. Normal in all sorts of power equipment.Silicon diode show up hot because it shows you junction temp, the LED might be the same thing. After all, INSIDE of the LED there is a tremendous power density at the emitter, relatively speaking. Lasers even more.470pF getting hot fits the bill of random ass capacitor that partially shorted or whatever, like in my unit.3W resistors get HOTLike I said, track the H-bridge control signal. The output is 100% isolated through the transformerIf the H-bridge is not commutating its not going to make a output.TR1 = isolation. If the H-bridge does not generate a AC signal to go through TR1 and then get rectified by the diodes, you will never see anything there.If you are sure of the schematic, then the M13 and M14 connection must be a fairly beefy signal, a signal that controls the gates of the transistors after going through the TR4 transformer. There should be a powerful signal there. My unit is different, they put gate drivers up on the IGBT,My machineControl signal -> IGBT driver stage (with isolated power rails, 20V) -> IGBTYour MachineControl Signal -> MOSFET (with no power rails)You get it right, M13 and M14 need to provide ALL the current needed to charge the MOSFET gates. So you have a power driver stage inside of the control panel?? The idea is that typically there is a "pulse amplifier" right near the output power transistors, that takes a little signal and makes it strong. I don't see any power source, so to me... its just pushing a big signal through. Sure mosfet don't need "current" to go into the gate, but they need to deal with charge, If you want it fast, it has to charge that capacitor up fast, which while small, still takes some muscle.And again, if there is a small short on a heat sink, you won't find that sucker. The heatsink is rated for like 200W or more, and say you are losing 2W... its like invisibleI am probobly thinking about this the wrong way, I don't have experience with that circuit, its confusing to me.If you put a oscilloscope on the gate of one of the Fets, what do you see? Clip it on with the machine off and then turn it on (with correct ground connection) so you don't destroy something. The signal should be around somewhere reasonable for a MOSFET gate control. Or just probe the output of the M4 transformer.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 12:49:06 am
content: I think this is the setup your machine is usinghttps://www.coilcraft.com/en-us/edu/series/a-guide-to-gate-drive-transformers/I hate it but thats my own opinion.You need to verify if this is happeningIf thats not happening, then there is no AC signal to go through the final transformer and get rectified into a DC signal. Replace motor with transformer in diagram, and connect the output of transformer to a rectifier to make your weld DC powerYou should be able to trace the signal , starting in a MCU probobly, all the way to those big transistors.

author: Circlotron
author_rank: Super Contributor
timestamp: August 22, 2024, 01:41:02 am
content: Quote from: DisasterNow on August 21, 2024, 04:11:48 pmAlmost. The mosfets are a in half bridge so they drive the transformer both directions, but the rectifier diodes are kinda sorta drawn as if the transformer was only driven one direction like most low power SMPSs. That is to say, it is drawn as if there is a main rectifier diode and a catch diode to take the current from the downstream inductor during the non-driven period. Given that the transformer is driven both polarities I would expect to see a full bridge rectifier.Edit -> My bad. Now I see it is a double forward converter, not a half bridge, so the transformer is in fact driven one direction only.And IRF460s. They were common 25 years ago, but much better stuff is available now. I wonder why they chose them? They are a good, reliable mosfet though, no problem. Maybe the price was right, despite the extra labour of fitting four each side.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2024, 01:55:27 am
content: Quote from: Circlotron on August 22, 2024, 01:41:02 amThe circuit I was inspired by was from the same brand (an inverter) and was actually very similar. I attached it in the first messages. So I had to review the entire circuit making corrections, the output part of this welder is exactly as I drew it, with 3 anodes on one side of the secondary, and 5 on the other. The 4 cathodes are cut, the output occurs on the large heatsink where the 4 output diodes are fixed. As for the mosfets, in fact they are old, but as for many other components of this board. I'm not sure, but the welder should be in the first decade of 2000. Thanks

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2024, 02:27:30 am
content: Quote from: coppercone2 on August 22, 2024, 12:32:27 amAs you say, of course the occasional short circuit could also be on some heatsink, but maybe I'll try to check if that capacitor C11 is ok (I'll unsolder it).I don't have any pulsating signal at the gates (tr4 should be a pulse transformer), but tomorrow I'll try again with the oscilloscope. But without reaching the gates, as said the signal to the transformer Tr4 should arrive from M13-M14 of the logic board, so I'll measure the signal in that area. The same signal should originate from pin 14 (QE) of the TDA1060 chip, and then pass into the IRF110. Tomorrow I'll check, but I think there is no signal there already (which should be a rectangular pulsating I think).Since you asked about the logic board (it is soldered vertically on the main board), I followed all the tracks, as you can see it is a board designed for different uses, and in mine they basically didn't use any resistors (all the pads are empty). So you can see well how the TDA1060 interacts, the operations of the LM324, and what the hybrid pins on the main board are connected to.(the various traces look confusing drawn like this, but you can clearly see the signal path that should drive the gates (pin 14 of the TDA).The TDA manual regarding the output of pin 14 says:To avoid double pulses that might occur at an excessively low mains voltage or an excessively high output current the output is preceded by a latch. The two outputs offer a choice of output current polarity, QC giving a positive current, i.e. a current flowing into the output, andQEgiving a negative current, a current flowing out of the output. The two connections have the additional advantage that the relatively large output currents do not flow through the Vcc and VEE connections, where they could induce noise.Thanks for everything.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 02:35:49 am
content: the h bridge (maybe its better to call half bridge full name)should have that signalIf its stuck, or non functioning, there is only either a DC or no signal, meaning no waves to go through the transformer.I am too tired to look at all this, but basically it can either be1) fried part that makes the signal2) fried power driver for the signal (1 and 2 might be integrated in that chip)3) fried component in the path preventing the signal from going through (either to ground or open circuit or a combination)4) fault signal turning it off (i.e. over temperature). It should have fault circuits that will disable the oscillator if something is wrong.5)signal is OK and bad end transistor

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2024, 02:57:47 am
content: Tomorrow I'll look better. The TDA1060 is powered, and for example on pin 2 it produces a Vz of 8.4 as per the manual (which in any case is not needed for my circuit). I would be for your point 4: some safety device of the TDA prevents the signal from coming out of pin 14 ( And it has nothing to do with the yellow LED turning on, because the signal does not come out even with that LED off. I think that by checking better the signals I have on the various pins of this chip, I should perhaps understand why no signal comes out of QE.Note: with or without short circuit, the temperatures of this hybrid board are not alarming, they seem normal to me.I will let you know.In the meantime, thanks for everything.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 22, 2024, 10:58:30 pm
content: Today I only had time to perform measurements on all 16 pins of the TDA1060 chip.The output signal from pin 14 (QE) is flat and a few mV, in short there is no signal to the small logic mosfet and therefore consequently at the ends of the TR4 pulse transformer I only have 13.7dc (which as per the diagram must arrive at the transformer).I will also check better the voltages on the various interesting pins:pin 10 EN: 9,7dc, i imagine it is intended as a high signal and therefore enables the output (I imagine the signal becomes low with the yellow led on, since it is connected via the operational amplifier to DL2).pin 3 FB: 3.6dcpin 4 GA: 7.5dcpin 5 mod: 12.6dcpin 6 DFM: 0.5dc, it should set a circle duty of 0.7pin 8 dx: 3.5, this sets the output frequency of the signalthe other pins are not important.Here's what the TDA1060 datasheet says about these pins:Remote ON/OFF switching: ENABLE input EN (pin 10)The output pulses can be switched on and off by applying logie levels to the TTL compatible ENABLE input. A LOW level causes immediate inhibition of the output pulses, a subsequent HIGH levelswitches the circuit on with the slow-start procedure.lf this facility is not required, EN should be connected to Vz, pin 2.Contro! loop sensitivity, stability, and feedback loop fault protection, FB and GA (pins 3 and 4)The device contains a contro! loop error amplifier, i.e. a differential amplifier that compares the voltage on the feedback input FB, pin 3, with the internal reference voltage. This reference voltage is a temperature-compensateci voltage source based on the band-gap energy of silicon.The contro I loop sensitivity is determined by the closed-loop gain Af of the error amplifier. Normally the output from the SMPS is connected to the feedback input FB via a voltage divider and a seriesresistor. The closed-loop gain of the error amplifier is set by applying feedback from the gain adjustment output GA, pin 4, to the feedback input FB by a resistor R3-4, see Fig. 8.To avoid instability a capacitor should be connected between the gain output GA and VEE· pin 12. A 22 nF capacitor will cause the frequency response to fall off above 600 Hz.The feedback input FB is internally biased to the HIGH level, this gives a protection against a feedback loop fault: an open feedback loop will make the duty factor zero.A shorted feedback loop (feedback voltage less than typ. 600 mV) causes the maximum duty factor input DFM to be internally biased to the lower leve! of the sawtooth waveform via a resistor of typ.1 krl, thus substantially reducing the maximum duty factor. This duty factor will then be determined by the impedance of the external voltage divider at DFM, pin 6, and the internal biasing resistor.Modulation input MOD (pin 5)The duty factor of the output pulses may be reduced below the value resulting from the voltages on the maximum duty factor input DFM and the gain adjust output GA by applying a lower voltage to the modulation input MOD. This input may be used with an external control loop, e.g. for constant­ current contro!, orto obtain a fold-back characteristic.lf the modulation input is not used, it should be connected to Vz, pin 2Operating frequency: RX and CX (pins 7 and 8 )The frequency of the sawtooth generator, and hence of the output pulses, is set by an external resister R7 at RX, pin 7, and an external capacitar C8 at CX, pin 8 (see Fig. 7). The frequency may be set between 50 Hz and 100 kHz and is virtually independent of the supply voltage.Maximum duty factor and slow start: DFM (pin 6)The maximum duty factor is set by the voltage on the duty factor input DFM (see Fig. 4). This voltage usually is derived from the stabilized power supply Vz, pin 2, by an external voltage divider, see Fig. 8. As the upper and lower levels of the sawtooth waveform are set by an internal voltage divider, the accuracy of the maximum duty factor setting is determined by resister ratios rather than by absolute values.In case of a short-circuited feedback loop (V3-12 less than typ. 600 mV) the duty factor input is internally biased to the lower leve! of the sawtooth waveform via a resistor of typ. 1 kD.. The maximum duty factor permitted in that case sets a maximum limit to the impedance Jevel of the external voltage divider at pin 6.During the flyback of the sawtooth the output pulse is inhibited. Fora 1 nF capacitar C8 at pin 8 this flyback time is 1 µs. This sets a natural limit to the duty factor.The time constant for the slow start is determined by an external capacitar connected between the maximum duty factor input DFM and VEE· pin 12, together with the impedance of the voltage divider at pin 6. This capacitor also determines the dead time before the slow start procedure for remote ON/OFF or when the current sensing voltage has exceeded 600 mV, see below.lf the DFM input is note used it should be connected to Vz via a resistor of 5 kil.Thank you

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 11:12:12 pm
content: Ok then you certainly found the problem.It sounds like something is telling the chip to turn off. A fault signal perhaps, or something that got busted.When you are sure about what logic inputs the chip should have to function, you can determine which one is different, and what might be the cause of that. I think this might mean your power section is fine, because its not even being turned on.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 11:13:31 pm
content: TTL is 5V. If you have 9V there is a problem, I think. A ttl signal is 0V low 5V high (ideally). 9.7 is very strange.It's not connected to Vz on your schematic. So that means the TTL input is getting double the usual.Usually the absolute maximum voltage input you see on a TTL input is like 7V.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2024, 11:32:47 pm
content: But the chip has a absolute maximum of Vz for all inputs, even if they call it TTL. Its enhanced TTL I would say.Can you measure the Vz ?I don't like it anyway, because the data sheet basically says, your not allowed more then Vz on any input, meaning... that 9.7V is 0.7V above the worst case 9.I would replace that chip for sure. It stands out. Its mad driftedThis is like Treez specifications. How much can you go above absolute maximum lol?!

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 12:10:54 am
content: I also think that the chip inhibits the output from QE pin 14.The datasheet for EN pin 10 actually says that it accepts the TTL signal, so it is assumed that it should enable the output with 5v and disable it with the low signal (this evening the yellow LED did not light up, it should lower the signal on this pin to zero I imagine. But as mentioned I have 9.7dc (seen the signal on the oscilloscope).Looking at the track of pin 10 (it is the signal that then passes over C4), it arrives at pin 5 of the LM324 (which is part of the operational on pins 5, 5 and 7).Vz is as per data, perfect, stable 8.4dc.I'll check further tomorrow. Thanks for everything.(I attach the TDA1060 datasheet)

author: coppercone2
author_rank: Super Contributor
timestamp: August 23, 2024, 12:12:13 am
content: Ok, you might wanna check with a meter (scope is not great for DCV).But the fact is, the datasheet says absolute maximum on a input pin is Vz. But your getting 9.7 which is way above 8.4V, which you measured.and it should be 5V to be in TTL spec!!!!!!

author: coppercone2
author_rank: Super Contributor
timestamp: August 23, 2024, 12:13:58 am
content: something is not right there unless the designers dont care at allabsolute maximum is absolute maximum, unless your boss is going to fire you before you get a respectable job

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 12:17:24 am
content: Yes, the voltages are all checked with the multimeter) with the oscilloscope I just wanted to see the type of signal carefully).Thanks, I'll do more checks tomorrow. I would have liked to try to figure out how to temporarily enable the output (with some tricks), just to understand if it's not an internal chip problem).

author: coppercone2
author_rank: Super Contributor
timestamp: August 23, 2024, 12:19:45 am
content: ehh check all the circuits leading up to that 9.7V however you can before you do that.Theoretically if you get 9.7V on a absolute maximum 8.4 V pin, its toast! I would consider that chip damaged at this point.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 12:19:57 am
content: Yes, I had seen that the inputs should not go beyond Vz (therefore beyond 8.4dc). At this point, but I'll check better tomorrow), the EN input is over 1.3v, but also at pin 5 I measured 12.6 dc! The others are inferior.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 12:21:09 am
content: I'll check everything tomorrow, thank you very much Coppercone. Good night

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 08:09:46 pm
content: I checked the voltages on the TDA1060 pins again, I confirm those I reported yesterday.For example, at pin 10 (EN) there are 9.7v (which does not comply with the datasheet). Below in the sketch I drew the part of the circuit that affects that pin, and what could influence it.Unfortunately I do not understand what could inhibit the output of the signal on pin 14 QE of the TDA1060 (it should be a rectangular wave).I think I will have to abandon this repair, my skills are finished

author: coppercone2
author_rank: Super Contributor
timestamp: August 23, 2024, 09:26:35 pm
content: Well you found the problem, it looks like its a damaged chip. For all you know the chip broke.If its going into a INPUT of something else, chances are its busted!The non inverting input of op amp does not consume current in that configuration, its just measuring!replace all the silicon stuff on the control board. It should only cost a few dollars. those are cheap parts. That op amp is the most cheap op amp in the world, and I doubt that controller is too expensive.All that shit should run you less then 15 euro.It could be as simple as some kinda problem with the power supply causing the chips to break.Anyway, its alot less of a problem then trying to replace all those power components, and cheaper.I would1) remove all the silicon cheap parts from the PCB (including the transistor and diodes, if you can figure out which diodes it is, or at least measure them)2) test all the passives with silicon parts removed, including the capacitors3) install new parts4) hopeSee I suspect, the op amp is getting something from a 310V rail. It probobly mal functioned. maybe something arced over like dust or whatever.310V near a LM324 is like if a house near a firing range got hit with artillery, its not very safe. or like a car ending up in the front of a store... (blues brothers)and check that temperature sensor.I would not put anything past a high voltage circuit getting into control siliconIf high voltage gets into a low voltage circuit, what it does is basically totally fucking random. it can break the whole board, it can find a weak part, it can jump around and degrade a bunch of things. it can do anything from explosions to almost undetectable damage.Its common, look up requirements for protecting keypads and touchscreens and such on industrial equipment, they want like double or more isolation! The keypad needs to have like a coating resistant to HV (1 isolation), and then have it electronics connected through another isolator (i.e. opto, transformer, etc). I think I Have seen one where they wanted double isolation and a protective film (triple isolation) for some medical weirdo thingWhat happen to that 310V rail if the power grid spike to 500V while your welding with a fast pulse or something? power section might take it but it can fry the digital side, especially if its cheap.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 10:22:51 pm
content: As you said, the 310 volts pass through two resistors (they are soldered vertically), R16 and R17, which lower the voltage to about 5.6 volts, which is certainly used to communicate to the control board the presence of an adequate voltage on the power part.I checked the thermal sensor (with hot air), when the temperature goes above 80°, it opens the circuit and the yellow LED lights up, so it works perfectly.The problem is that I do not have a reliable schematic of the small hybrid board (there are some sketches found online, which I had attached previously, but they do not match much ...), so apart from the two chips and the mosfet, the rest would not be easy to identify. It must also be said that for example the TDA1060 and I believe also the LT324 are obsolete and perhaps can not even be found anymore. This is a big problem.Would it be possible to unsolder at least the 3 largest chips, and check their efficiency on the bench in some way? This would make sense, for example if I could verify that the TDA1060 comes out with some signal from pin 14, then it could be efficient.Thanks

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 23, 2024, 10:26:01 pm
content: I attach the only sketches I found online of this small control board (but as you can see, on mine many components are not mounted, all the resistors for example etc.)

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 03:10:18 am
content: LM324 is standard part, still available. The other part I see you can buy from website for 5 euro.If you are hell bent on testing a 2$ lm324 chip, you can look at the data sheet for performance tests. You would need to desolder it, put it on a adapter to soic, and do all the performance circuits on a breadboardthe other chip IDK, its complicated.now for the ceramic card, I never worked on one, I won't give you advise. I just know if its silver on ceramic, you want silver bearing solder so you don't dissolve the traces. this card is a module purchased from someone to do a complicated function drop in. I have seen some people like 'mikeselectricstuff' repair these kind of cards. Theoretically if something is soldered to a ceramic, its the same thing as a PCB, other then that silver related nuance.in practice its brittle. If something did fry on there or it over heated before, it could be damaged in such a way that makes the ceramic extra fragile. Also ceramic is a good heat conductor to PCB, so it might need alot more wattage to remove parts. You would need to do research on this, I never tried.I have made my own ceramic silver pCB traces, the only thing I noticed is that while somewhat strong, its not that strong, never ever yank at anything on there.I think you need a second opinion on that chip. I wonder if there is a special extended voltage range series or something, but I think its broken. those cards are not invulnerable and a welder is exactly the type of equipment I would expect it to break in lol because their evilIf I just decided to randomly try it, I would get very thin solder braid and see if I can suck any solder of those chips. you need to be precise with the iron not to scratch or knock something off

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 03:24:02 am
content: if you want to persue the theory about the ceramic card, the hard way might be to remove the whole card carefully from the PCB, wire it into a bread board, and then make a mock up circuit that tests all its functions. bit of engineering effort . you just need to map out all the signals that it expects and test it for realistic performance on dummy loads. Not sure how easy they are to remove though.I am out of ideas on this one for nowOddly enough, the IRFD110 was one of the part that broke on my miller. They had like 10 of them in a bunch, and the PCB literarly made a hole from sparks near those chips. I had to replace that card because it was totally messed up with way too much arc damage. it looked like it got shot by a ray gun

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 24, 2024, 12:30:09 pm
content: Of the 15 pins on the logic board, those that reach at least one of the two main chips, and which could therefore inhibit the signal, have voltages in the rule. This means that the output signal from QE does not come out due to a fault somewhere on this hybrid board, and not on the main board. As you also said, desoldering and soldering on this ceramic board is not easy, I would also add that there is a layer of protective lacquer that would increase the problems. I could also do a desoldering test (I would use the hot air desoldering station); but at this point I can say that I have done everything possible, the fault has been (more or less) identified, but the repair is too complicated.It was still a nice 'journey', I studied a circuit that I had never had the opportunity to repair. A heartfelt thanks to Coppercone for all your advice received, you were very kind. Thanks

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 07:19:02 pm
content: It's not that bad to repair it. You need to suck out the solder to remove the chip and hot air should get rid of the op amps. You can pack the board with putty or use tape to protect the other parts.The conformal coating is light weight, it should come off no problem, especially after all this time.Its easy to try, I would not recommend giving up at this point. You might be surprised how well it goes.I would only give up if you plan on giving it to someone else to repairmy welder just got destroyed by a beetle and I need to figure that mess outThe military has giant ceramic boards (2x2 feet) that they used to repair for jet airplanes maintence systems and stuff

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 07:22:43 pm
content: for removing parts SMT there is also the "pakistan style" trick where you bend copper wire around the chip so it can screw into the barrel of a soldering iron. After enough time your thick copper wire gets hot enough to heat up all the contacts at once. It might actually be useful if your scared that hot air is going to be too hard to control (which it often is not, usually the problem people write about hot air comes when there is tiny parts around, i.e. 0402 or 0201 (that you need a magnifier to see). All your parts are bigPractice desolderin a chip on a normal PCB, then you know you have the right settings, then do the same thing for ceramic pcb, possibly you might need to increase the heat a little bit or do some very gentle pulling (no yanking) when its hot if there is some glue

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 07:24:18 pm
content: Oh yeah, but there is another method you can use to increase your reliability to 100% for the repairyou cut all the parts off at the base of the part with flush cutters (fine tip), remove the part, then heat each lead individually and pull it with tweezers. it wrecks the old parts but its what I basically always do because its just betterI would only bother desoldering a part properly if its worth at least $10 and I have a feeling that its ok (i.e. to isolate part of troublsome circuit)this is more then good enoughhttps://www.amazon.com/Xcelite-170M-General-Shearcutter-Diagonal/dp/B0002BBZISthis is total overkillhttps://tronex.descoindustries.com/Tronex-Catalog/Cutters/Tip-Cutters/5049/then you solder on the new parts with a soldering iron, you can even glue it down with a tiny dot of hot glue to make it easy. Wick out the holes with fine solder braid, or a solder extractor, or if those two fail, you can use a air blower to blow out the solder to the other side (messy and requires very detailed inspection to make sure you did not short something with a errant solder blob)You only have a SOIC part. The tear drops might start when you have a heat sinked no-leads part, then you can't cut them off. A SOIC is just a squashed dip, you can cut them off! it has legsAnd Ceramic is not that weak, i mean its weak compared to fiberglass but I have been using this ceramic substrate (ceramic utility knife blade) for my experimentsit survived multiple drops on the concrete floor and around 5 heat cycles, one to 1300C and 4 to 1000C, before it broke when I wanted to see if it still cuts into a bottle cap after all that (I forgot that I had initially sanded the edge off with diamonds to make it safe, otherwise it would probobly be fine). I even dropped it hot when it was like 600C the first time I took it out of the oven, because it slid off my oven plate when I put it into my cooling insulated brickhttps://www.sliceproducts.com/products/ceramic-utility-bladesthey work for knives, I use them. I am telling you, your repair is easier then you think . Those ceramic substrates are not shitty clay pottery, its a hard core engineering material, they do all sorts of things a typical ceramic person does not do, like x-ray? porosity tests, density tests, cracking inspection, etc before it gets approved for circuit card use.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 24, 2024, 09:48:18 pm
content: I admit I thought about giving up on the repair, I spent 1 month on it. We understood together where the problem lies. However, your further encouragement convinced me to continue. I have enough manual skills on how to unsolder or solder these components, perhaps I could have some problems in soldering the LM324, the TDA1060 will not be a problem.I will proceed like this: first I have to unsolder the entire small hybrid board from the main board, there are 12 solder pins (3 are not used); so I can then have more manual skills, and I will start by unsoldering the TDA1060 and the LM324 calmly and patiently... If the work is done well, with all the pads still usable, then I will try to order these 2 chips from the Chinese.That seems sensible to me, right?Be careful though Coppercone: let's not forget that in any case there remains that occasional short circuit that I have not yet unfortunately identified (unless it is a consequence of these 2 chips, but I do not know). In the meantime, thanks again, I will proceed calmly, but I will update the situation here

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 09:53:33 pm
content: yeah it should work so long you don't drop it or get forceful with the heater

author: coppercone2
author_rank: Super Contributor
timestamp: August 24, 2024, 09:58:10 pm
content: just don't forget you might want to use the silver solder. I don't know exactly what that board is, but it could be silver glass, meaning it will dissolve in to normal solder, and it can leechhttps://www.ebay.com/itm/116004675563a few inches worth should do, if you can find it in smaller quantity.they are very cheap with silver, so you don't have much to work with. I never noticed anything on my DIY ceramic silver PCB with the leaching, but I trowel it on, I know someone would get shot if they tried to put that thick a layer in a normal factory lolI do have some piece of shit russian inductor (well actually its kind of nice) with metalized silver ceramic pipes to feed wires into a chassis. I noticed when I start feeding regular solder into that, the "silver" on the pipe walls started to disapear. But I assume a soviet worker ripped them off and carried out most of the silver paste on the bottom of his hat, leaving the absolute bare minimum on the walls of the ceramic feedthrough. To get wires into holes, they would use a ceramic pipe, metalize the interior and exterior, solder it into a hole in the chassis, fill it with silver bearing solder, then use it like a interconnect. This was for a hermetic sealed part with a big gasket on the bottom. Then it could be filled with dielectric gas, or be water proof, or whatever they needed it for

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 25, 2024, 01:23:21 am
content: I preferred not to unsolder the hybrid board, in addition to the normal soldering on the back side, all the pins had the soldering cone also on the board side, and being in the part that faces the voltage regulator heatsink, it was impossible to work. I then unsoldered both the TDA1060 (which came off immediately), and also the LM324 (more difficult, it was completely drowned in the protective lacquer that prevented the heat). No damage to the pads, let's say that I then cleaned lightly with the braid but not much, and scraped the pads from the lacquer. I protected the other areas, but I see that in the lower part of the small chip there was a lot of lacquer that has taken on a brown color, but I don't think it's a problem.I only have lead solder wire at home, I would try with that maybe.Looking at the photo I have a doubt (the board is in the lab and I'll see it tomorrow): has the base of the small electrolytic SMD capacitor melted?But I don't think so, I was at 370°, but it was all covered by a protective aluminum layer.

author: coppercone2
author_rank: Super Contributor
timestamp: August 25, 2024, 05:29:09 am
content: those bases suck their easy to melt i doubt it damaged the pad you can probe it with a LCR meter near it if you wanna see if its still connected with low ESR but I think its OK

author: coppercone2
author_rank: Super Contributor
timestamp: August 25, 2024, 05:30:38 am
content: you can also probe the opto coupler in circuit carefully to see if it works by hooking up a power supply current limited to one side and dmm ohm meter to other side, might be a good idea to try that before you reinstall parts

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 25, 2024, 02:42:43 pm
content: Quote from: coppercone2 on August 25, 2024, 05:29:09 amMaybe it's just all the lacquer that was covering the chip, I was blowing hot air in that direction and it probably got under the protective aluminum. First I want to try to clean this lacquer from the board, with isopropyl alcohol I don't solve anything, I read that acetone is supposed to clean the lacquer. Then I'll check that capacitor (but I don't think anything happened to it).

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 25, 2024, 02:44:21 pm
content: Quote from: coppercone2 on August 25, 2024, 05:30:38 amWhich optocoupler are you talking about? I don't think I have an optocoupler in my board (both hybrid and main).Can you explain this check to me better? Thanks

author: coppercone2
author_rank: Super Contributor
timestamp: August 25, 2024, 05:30:46 pm
content: on the lower left of the close up picture I thought i saw a 4 leg opto coupler chip (dip -4)I see its a IRF 110 now. never mind. mosfet99% of the time, dip 4 chip is optocoupler . welding machines seem to have 4 pin mosfets

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 25, 2024, 06:14:06 pm
content: I imagined you were confused, yes it is a mosfet and I imagine that it amplifies the square wave signal that should come out of pin 14 QE of the TDA1060.I checked that dark part better after desoldering, in reality in person it is much less evident. It is just a part with a lot of lacquer, tried with acetone but it does not clean. Oh well it does not matter.

author: coppercone2
author_rank: Super Contributor
timestamp: August 25, 2024, 06:16:38 pm
content: nah you need special solvents.THF works good. Flux remover (like the rosin flux remover from the can) works good, its some kinda freon.It basically makes it "constrict" and lose adhesion, then you can just peel it off with a stiff brush (ESD SAFE ONLY)ALcohol has little effect, Acetone I am not sure.The best stuff is herehttps://mgchemicals.com/products/conformal-coatings/conformal-coating-stripper/conformal-coating-remover/It has acetone, combined with 2 other solvents. Solvent combination is necessary. Often when you mix solvents, its better then just pure solvent for dissolving. They do experiments to see which mixtures effect the glues the best.Alcohol is used for rework, so they pick a glue that does not get effected by alcohol too much.Now, there are stronger coatings, like paralyene and stuff... that are a bitch. Those you need to use heat, i.e. a pace lap-flow tool, which is basically a scraper that is resistance heated. You heat it up to a depolymerization temperature of the glue, and then scrap. But that is a expensive vapor deposited coating (vacuum oven required). Usually only found in government equipment, like space parts. I don't think I ever came across it, but there is plenty of info about it.Also, epoxy is kinda hard.. but its not the best coating anyway.I found that basically MG chemical conformal coating remover worked on anything I ever come across. If I wanna do a 'neat' job, i.e. a repair on a nice board, where I don't want to risk peeling the coating, I use the lap-flow scraper tool at low temperature to remove the coating, or a abrasive rubber burr, followed by damp q-tip cleaning of the residue.Being able to work on conformal coating nicely, is a skill IMO... I am sure there is people that are really good at it, at the repairs department of NASA or something. I find it completely obnoxious. That is the same skill as a beauty salon worker, work with smelly chemicals and skin peels.. They use the same tools too. I imagine a slightly overweight woman with streaks in hair and 1/2 inch long nails doing this job "nicely" while on phone. I just recommend dousing and scrubbing with a ESD safe brush when its all deformed, followed up by ultrasonic cleaning (its really hard to get the board "clean" at a magnifier level, there is always little curls of coating left behind.

author: DisasterNow
author_rank: Regular Contributor
timestamp: August 25, 2024, 11:22:03 pm
content: MG chemical makes excellent products, I have the varnisch 4226A. However, I saw that with hot air (well, I was at 370°, but I think it works even at much less), the lacquer melted and then when it was cold, all you had to do was scrape it off easily. I always remove the flux with isopropyl alcohol, but I found this lacquer to be really tenacious. But as I said, for now I only care about cleaning the pads well.Now I'll see about ordering the two chips (I think from the usual Chinese mega shop), they usually arrive after 3 weeks. I'll leave this topic waiting, I'll come back to it after replacing the two components.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 05, 2024, 02:06:25 pm
content: Update: I replaced the only two chips of the small logic control board (TDA1060 and LM324) to see if anything changed.Before I never had a voltage at the output (maybe only when I had those occasional short circuits). Now the situation is as before ONLY if I keep the output current potentiometer at maximum; but if I lower the potentiometer even a little (and then to the minimum current), the short circuit (I see it from the light bulb in series) is continuous, and now I hear a constant 'tic' noise (its frequency decreases with the mains voltage, and increases if I lower the voltage with the variac). I have not understood exactly where the tic comes from, but analyzing with a microphone I seem to understand that it comes from the power transformer (TR2 in the diagram). During this short circuit that is now continuous, the only components that I see heating up are R11 (180°) and C11 (not too much, but it heats up only with the short circuit). But now if I see the output signal of the welder, I have a voltage 'dirtied' by the short circuit as you can see in the image; the frequency of the 'tic' that I hear, I think it is like the time interval where the signal returns to zero and then rises again (about 500ms). In short, now with the replaced chips something has changed, but I don't understand where the short circuit comes from.

author: coppercone2
author_rank: Super Contributor
timestamp: September 05, 2024, 10:05:30 pm
content: im too tired but it made me think of a active snubbermy power supply had a snubber / crowbar whatever that kept turning on, it was over voltage protection. it made a terrible clicking noiseWhat I would do however is try to determine why those chips broke and what other chips might be broken. it could have spread through the power rail. So if two low voltage silicon chips died, chances are more are dead. its like lightning struck a house with those welding machines, from what I see on my dynastyJust a good bet might be to keep replacing things connected to that power supplyI would guess the IRF and the BD transistor are suspect, I think their gates/bases could be messed up if the chips nearby were messed upclearly you found the right area. little transistors can break in power supplies that are near big transistors, and the opto coupler might be messed up too. you have no way of knowing when it makes a trigger signalit is progressif those chips got damaged they started sinking energy, so hopefully the damage is localized to that area.the fact that you need to turn it up all the way to do something, it might mean the gain of the error amplifier or whatever you wanna call it is messed up. so if a op-amp is trying to drive a transistor, and the gain on the transistor is bad because its damaged, it won't give the response until signals are very strong. things get "skewed"imagine the handle on a bicycle break was super badly bent and also loose. when you push it 90% of the way, you finally get out of the 'loose' region and you hit the break a little bit, but it bearly moves the break line even when its fully pushed in. its not 100% disconnected, but your not getting the correct amount of leverage because its deformed and loose, so the input you give it does not bias the system properly. damaged transistors may end up doing something like this, sometimes you can think of this as 'low amplification' or 'poor response' or 'lost sensitivity' or 'low gain' in a control looplets say you some how burn the metalization off a mosfet and the capacitance is less at the gate, then if you give it 5V, it does not have enough charge to properly trigger the fet, if you give it more then that, you punch through the oxide layer and break it, so its effectively broken, the response parameters are wrong. with BJT its similar, that is the current you give it does not create the correct amount of current flow. in either case, it still has a transistor like response, but its all wrong for the system its in and in a stressed mechanical state . MOSFET are charge devices, charge is proportional to voltage and capacitance, if you have less capacitance (missing metal), the normal voltage does not contain enough charge on the transistor

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 06, 2024, 02:12:36 pm
content: As soon as I have time I will repeat the tick recording with a better software, so I can see the exact point better, it should still be near TR2 (power transformer, I have two images below).Looking at the output signal in fact it would seem that something at each tick enables/disables the output voltage for a fraction of a second, and that when it is enabled there is still a short circuit in progress.On the control board, in addition to the two chips already changed, the only interesting thing would be that IRF110 marked in an image with a red arrow, but since it is covered by alcca, the acronym is not readable (I deduced IRF110 from the hybrid diagram found online, but it is not entirely identical to my board).As already said during this short circuit the only components that heat up are R11 and C11 (I have the images below, also of the part of the circuit that concerns TR2-C11 and R11).Other interesting silicon components could be the two transistors (T2 and T3) that are in the part of the circuit that goes to the igbt gates, I could also replace them, but checked on the board they do not seem to be faulty.For many components, a replacement problem could also be that their leads are drowned on the large rear tracks, they have tinned everything together (as in the image some examples circled in red).

author: coppercone2
author_rank: Super Contributor
timestamp: September 06, 2024, 08:48:59 pm
content: i heard a clicking coil before when a power rail was damaged for a active crowbar type circuit (over voltage drain transistor). it shorts out the rail and makes the transformer click like a solenoidthat whole circuit with R10, its a snubber,.3.9k = bleed resistor (drain), C12 R10 = snubbersnubber are known to fail because they take a beating. a partially shorted capacitor could be a phenomenonThe IRF110 or IRFD110 is common in welding machines, mine had a broken oneand there is another 2 transistor, one to the left of the picture, the small footprint one, its suspect since it on that PCB, the other one is left to the IR110and I don't know what C11 does its confusing to mealso tantalum caps are known to short out and go bad, especially cheap ones on equipment thats not derated properly (aka non-goverment)so on your ceramic board there is 3 suspicious transistors and 2 tantalums that are just a known trouble maker in cheap equipment unless the designer happened to be smart.the ceramic are better on ceramic PCB, they usually break for mechanical reasons, they are hopefully OK. But rule nothing out if there was a over voltage you know, its like a moose got into a china store. Usually the more complicated parts break first and sink the fault voltage and protect the basic stuff loland if there was a over voltage, tantalums are sensitive to that. and theyexplodewhen they fully go, it will shatter that board like a small fire cracker put on top of a soup cracker. they have a bad enough reputation that you might want to deal with that, because it can be a ticking time bomb if the circuit was stressed, which it might have been. If a tantalum really explodes it can put a literal hole in a fiberglass board, ceramic will likely get shattereddebugging the board individually is a good idea, if you can manage to hook it up, that is the right way to do it

author: coppercone2
author_rank: Super Contributor
timestamp: September 06, 2024, 08:58:48 pm
content: if the 3900pF capacitor is shorted or partially shorted, a 10 ohm load on that driver WILL make it click and eventually burn up that resistor, 10 ohm load is rather low, its only 10 ohms for the frequency that is supposed to go through the capacitor, for the welding energy it should be open circuit

author: coppercone2
author_rank: Super Contributor
timestamp: September 06, 2024, 09:00:44 pm
content: also if you scrape the goo off the transistor it will be easy to read, the top does not need goo, its just hard not to get it there if its dip coated. ideally they would mask all the chips and keep the goo off the top, but it would be tons of extra work only the repair man can seekeep in mind, goo can make failures worse. it makes it more difficult for a component to vent. what you want is energy going above the PCB. if you have a submerged part, it will explode harder. for electrolytics your supposed to put tubes on them if you pour sealant, so the top of capacitor is unsealed and can open up to vent smoke instead of failing to open up and explode!if you elevate a part off the PCB with a air-gap, it will burn up and leave the board alone. if its glued to the board it will transfer more heat into the PCB and wreck it!very high end boards, instead of trying to use the board as a heat sink, they use bigger parts, and elevate them with standoff from the PCB, that way they can happily fail while glowing white hot without destroying the circuit card. I had a ton of board repair work from over stressed transistors that perform no RF function. if they elevate them from board by 5mm with rivet standoffs and solder them there, it would be 100% fine

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 06:38:52 am
content: Quote from: coppercone2 on September 06, 2024, 08:48:59 pmI tried to clean the lacquer on the IRF110(?), but without success. Maybe I should heat it with hot air to remove the layer.The one next to it should be a transistor, it is on the pin circuit of the logic board that goes to the relay.The other 3-pin on the left, from the diagram found online, should perhaps be a double diode, and on the I_sense circuit.The tantalum capacitor C17 is on the signal that goes to the EN pin of the TDA1060.If I knew all the values ​​(but I don't), I would want to change all the components of the logic board, or at least those most suspect for the short circuit.C11 certainly heats up at the moment of the short circuit, from 30° to about 65°.Do you mean to try not to power the main board with the mains voltage, and try to power the logic board only from the M2 pin (13.7dc)?

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 06:46:10 am
content: Quote from: coppercone2 on September 06, 2024, 08:58:48 pmMaybe you mean C12 of 4700pF? You can see it well in the third image above, together with R11 and R10: the 10ohm resistor is new, I changed it (even if the old one was ok). While at C12 a lead had broken (bending it), I think I had measured it and it was ok, then I resoldered it.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 06:51:05 am
content: Quote from: coppercone2 on September 06, 2024, 09:00:44 pmOn this board they exaggerated with the protective lacquer, it could have limited the heat dissipation of many components; in addition it complicated the measurements (I had to scratch all the points to have contact with the multimeter tips).

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 06:59:11 am
content: yeah powering it from a lab supply and giving it your own signals, if you can figure it out, its a very powerful troubleshooting technique, if you have sufficent understanding of the circuit.the 10 ohm resistor in series with a capacitor is a classic snubber circuit (RC SNUBBER). The resistor in parallel with it is just a drain circuit I think, to make sure charge drains off if you turn the machine off. The cap and 10 ohm should not get warm at all unless there is AC current flowing, you can even calculate the dissipation, that is the ESR of the cap and the current flow through 10 ohm resistor.That component is fairly.. . high energy, being a snubber, you should replace it

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 07:07:02 am
content: for replacing those parts, I don't know honestly...I just don't know enough about how this circuit works to understand why it might be clicking like that. Usually their in current limit with a short like you think.A potentially bad idea might be to hook it up to a 12V car battery on the offending board, even a power component might blow up or smoke to tell you where the short is.haha, I wonder what would happen if you put a big contactor on a car battery, hook it up to the welder where there is a short, and see what happens if you give it a momentary contact. or just spark the terminals

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 07:08:58 am
content: current limit typically behaves like thishttps://www.cui.com/blog/fundamentals-of-power-supply-over-current-protectionlook @ hiccup modePerhaps the most common implementation for current limiting now employed in power supplies is known as hiccup mode. This mode of over-current protection can be thought of as an active version of fuse protection mentioned earlier in this discussion. With hiccup mode current limiting protection, the output voltage of the power supply is shut down when an over-current situation is detected. After a specified waiting time the output voltage of the power supply is re-established. If the over-current situation still exists, then the supply repeats the shut-down and wait process. If the over-current situation no longer exists, then the power supply continues operating in the normal mode (Figure 6).

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 07:12:38 am
content: Quote from: coppercone2 on September 07, 2024, 06:59:11 amIn the next few days I can try to power only the logic board (I will try only from M2 and from M16 gnd).R11 from 10ohm heats up due to the short circuit; I did not have C12 at home, when I bent it it also lost part of the blue cover of a rheophore. The ideal would be to start changing various components, such as C12, C11 and the two transistors on the IGBT gate circuit.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 07:16:22 am
content: Quote from: coppercone2 on September 07, 2024, 07:07:02 amIf I wanted I could not use the bulb in series, now after replacing the chips it always stays on. The hope would be that it would burn the part in short circuit, but I would not want to burn other parts instead...

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 07:16:47 am
content: why would a short circuit heat up a resistor with a capacitor in series???If there is a short circuit, the voltage on the rail would actually be LOWER and even less current would flow through the 4700pF capacitor.The 10 ohm resistor would be hottest in the open circuit condition, where there is the highest voltage across it.At least that is one simple way to look at it.But I guess it might be getting hot from the supply turning on and off and making a big fat square wave. So the hiccup ripple is heating the capacitor.?

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 07:20:25 am
content: you can disconnect that circuit from the transformer and put DC across it. If any current flows through the 10 ohm resistor @ DC, then the capacitor is shortedIf no current flows, it means its just the hiccup heating it. I don't know much about how those supplies functionand the possibilities for hiccup mode:1) there is a short and its responding2) the control loop is detecting a short circuit that does not exist (bad circuit)Disconnecting the transformer from the circuit can make probing alot easier, its mad annoying if there is a low impedance winding @ DC essentially grounding everything to miliohms of resistance from + to -

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 07:22:13 am
content: Quote from: coppercone2 on September 07, 2024, 07:08:58 amIt should be like this, we have this short circuit that is not easy to detect (at least for my skills), no smoke, burning smell, damaged components. Maybe as we said at the beginning of the topic it could be hidden under one of the 3 large heat sinks, who knows. And this short circuit inhibits the output.Thanks for the input Coppercone

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 07:24:04 am
content: actually I recommend doing that, I fixed some linear supplies when i finally decided to disconnect the transformer and it got alot less confusing and easier to measureDisconnect transformer and give it a small low current DC signal to see what it does and if it makes senseit felt much more mentally cleaner to me to measure and understand the circuts

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 07:29:17 am
content: Quote from: coppercone2 on September 07, 2024, 07:16:47 amThe capacitor C12 does not heat up at all, it is only R11 that reaches up to 190°. Not even R10 in parallel heats up. I will do better thermal checks in the next few days, now it is easy to go from a board state without short circuit (potentiometer at max), to the short circuit state (just lower the potentiometer by a few millimeters).

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 07, 2024, 02:38:55 pm
content: This is the audio of the tick that I hear in the power transformer sockets, while on the board I have the short circuit

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 06:29:38 pm
content: Ok, the capacitor is very low ESR, the resistor is high resistance (10 ohm).I think I saw this too, when in hiccup mode, snubbers on a power supply get hot. thats normal. So long it does not get hot at DC its fine.but if the cap was TOTALLY shorted, it would not get hot either because there is no voltage drop.

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2024, 06:32:47 pm
content: That tick is weird, I never heard one at such a low frequency before, it sounds like a spark gap. But again it says hiccup mode is 'programmed' by a time constant, so maybe that is the standard for welding machines. I only have experience with lab power supplies that are usually built to be verrry responsive.I am thinking about it conceptually, some how the circuit needs to measure current.If you can figure out how its measuring current (transformer, magnetic sensor (i.e. LAM module) or resistor), you can measure it to see if there is a over-current condition at the input to the current measuring loop.For instance,-if you have a magnetic sensor that has a 0.01V/Amp response, you could measure the voltage at the output of the sensor to see if there is actually a over current while its clicking.-if there is a series resistor, you can measure the voltage drop along the resistor to see if there is a high voltage drop corresponding to a Short-if there is a transformer, you can measure it too, but I forgot about how those current measurement transformers work lolBecause if you have problems with the silicon, its entirely possible for there not to be a short, but the power supply to behave like there is one. If there is op-amps what you have is some circuit that converts the current signal to voltage to make a threshold related decision (comparator etc).Like how it might work1) current sensor gives output voltage range from 0 to 10 volts (maximum current)2) current sensor is connected to feedback network that does nothing until the voltage gets to 9.5 voltsSo if you see that the current sensor is putting out 2.0V, but the network is responding like its seeing a much greater voltage, it means some silicon is messsed up. But if you see believable signal it means there is really a short some where.And you can test the control board too if you figure out which signals it wants to see if it trips over-current at the correct feedback signal, but be warned, sometimes this requires ALOT of supplies to bias everything. if you get mideval on it, you could use battery packs and voltage dividers (AA or larger cells recommended) lolALso, if there is a current sensor, and there is a short, you kinda 'isolated' the source of the problem to the circuit with the current sensor, not the circuit before it, unless some really evil shit is going on.I am thinking you should get some exacto knife, right angle screw drivers and big soldering iron to check out those chips under the heat sinkhttps://www.arestool.com/products/5-piece-ultra-low-profile-offset-screwdriver-setthese are good (on amazon too) for dealing with evil heat sink fasteners, if you have something in the way that makes removing the part too hard.I finished replacing the parts in my miller dynasty, im scared to try to turn it on again lol

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 07:10:15 am
content: I believe the current control is performed by the current transformer TA1. On the sketches found on the internet of the control board, they stated that the resistor R34 determined the output current. To this TA1 there is a trace that reaches the pin M3 of the control board (they call it I_sense). However, I do not understand how this I_sense signal works. Perhaps it is this current control that for overcurrent resets the output voltage with a time constant as I had measured with the oscilloscope.The resistance between pins 2 and 3 of TA1 is regular as in the diagram (2.8ohm); pin 1 of TA1 is connected to a pin of the power transformer by the red cable seen in the photo below.I would easily remove the heat sinks (by drilling the rivets), but the problem would be to unsolder the diodes or the IGBTs, they have the rheophores drowned in the large rear tracks.Let me know when you turn on your Dynasty welderI attach the images relating to TA1 (including a description of the sketch found online, where they focus on the R34).

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 07:15:29 am
content: ok I think I get it, r10 and r9 form a shunt that there is a voltage drop along that is connected to that transformer that steps it down to a voltage compatible with the control circuit. R34 is the resistor you normally put on current transformers, they have a load resistor.Where that connects must be a rectifier integrator or a ADC that trips somethingYou get a AC signal proportional to the current going through the R10 and R9. That signal is possibly rectified by that diode (not sure), possibly integrated by a capacitor, and it could go into that chip, either as a AC signal or a DC signal. Find out which pin of the chip it goes into if it goes into the chip

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 07:20:25 am
content: that trace out you did on the other page with the sky blue trace does not make sense to me, it looks like the current signal just goes into a bunch of grounds through parts. I think you missed a path that goes into the IC.

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 07:22:17 am
content: I think that it must be connected to Pin 11 of the TDA chip some how, unless they did some weird stuff and not used the chip functions (I have seen this rarely on IGBT driver or something, but oddball). I think they used the chip over current function, its logical.You could probe pin 11 of the TDA chip to see what it looks like while the welder is hiccupingIf its right, it should look like a periodic wave form of some kind (sawtooth, spikes, whatever) that corresponds to the current overload condition. if its just a boring high DC, there might be a problem.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 07:48:25 am
content: It was not easy to reconstruct the entire scheme, both of the main board and the control board. As you can see, my control board, on this welder, is missing many components. In fact, many traces do not reach the two chips, especially due to the lack of almost all the SMD resistors. The I_sense signal, as you can see, stops at that SMD ceramic capacitor.Pin 11 of the TDA1060 was not used and they connected it to the GND. However, as soon as I have time, I will do all the checks you suggested. For me, a circuit of this kind was an absolute novelty, but I must say that I was passionate about it. This would be a backup welder (I already have my Telwin), but it is certainly a good learning school.The short circuit must be there somewhere, the light bulb that remains slightly on indicates this. Thanks Coppercone

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 08:07:47 am
content: I don't get what Isense is doing thenits just going to a grounded diode? I think something is wrong because... how can that control anything.I wonder if one of your grounds, IS the short?The sense line simply has to go into a component that can have the welder make a control decision.If its just capacitively coupled to a diode that is connected to a capacitor, what is the point??? They put a transformer, a wire, and numerous components between two boards. It has to do something. That current transformer is a one way thing. It can't do anything to control those big power components. It has to go into that chip some how and make it decide there is over current. I am thinking that one of your grounds is the short, or you missed a trace.What could I be missing?

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 08:13:57 am
content: are you sure its not going into that thick film resistor (the one that looks like a shaded area) ?All those grey spots are resistors that are printed with silver ruthernium ink, I think. That way its ultra stable, the temperature coefficent is all matched, and a laser adjusts it during manufacturetheoretically if one of them is busted you can scratch it out and put a resistor on top of it that might drift a little but it probobly would work fine. I am sure someone had that circuit working on a bread board before it was made nice on some crazy hybrid ;PEdit: Oh I see, I think you thought that the grey areas are missing parts, no.. notice there is 0 resistors in that circuit? each of those should be a resistor. Its part of the appeal of making it. YOu don't order parts, you just draw everything you can on the ceramic. The benefits is1) its heat sinked to the alumina substrate2) its thermally linked3) its thermally matched (drift)4) no inventory requirement5) laser tuning possible6) possibly more reliable because no solder joints, in one sensebut of course that construction method has plenty of demons. its used mainly for minimizationhttps://www.celanese.com/products/micromaxThe sad truth about that, from what I have seen, is that the "potentiometer" guy on a assembly line is HATED by low production cost oriented management. I am not sure if they save any money trying to get rid of potentiometers, but they go crazy trying to do it. I knew a developer like that. He went loony tunes when it came to potentiometer adjustments. I personally think alot of those circuits would be fine with potentiometers and still be well within spec, outside of "manufacturing engineering" neroticness . For some reason if they get rid of a potentiometer its like they climbed mount everest... .while half the time the engineering cost is never made up in the life time of the product lol, and it makes revision planning insane.. don't let that ceramic scare you lol. also there is a inate fear that they might have some kind of EM problem involving goverment regulations (often unfounded) in a foreign country they don't even know the laws for (leads to crazy over engineering)engineer 1: NOW WE CAN LASER TRIM THE GATE RESISTOR INCASE THERE IS A SLEW RATE PROBLEMengineer 2: would it kill you to just adjust the schematic to change out a 0.08 cent resistor?engineer 1: *foaming*engineer 2: what if you need to put a ferrite bead?engineer 1: *siezes*then you might end up with a through hole resistor bent into place with a small ferrite bead on it, soldered into the "perfect" hybrid circuit that has been ground with a dremel by a emloyee on the line because they can't get the ink screen remade . I imagined it but it seems like it can happen, with db's to spare.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 02:18:25 pm
content: Coppercone, you hit the nail on the head with the resistors on the small control board. I thought they were missing on my board (I thought the board was used for different inverter machines, with different uses, and therefore mine didn't need those resistors). In fact, if you look at my image of the board where I drew the various traces in light blue, I had put a red x on all those resistors. In fact, everything seemed unreal, with traces that ended in apparently empty pads! After your input on this type of non-physical resistors, but only with one layer, I checked better. I think you're right.For example, I scratched one of these surface resistors that is on the I_sense signal, after the 3-pin diode (attached image), and measuring the resistance coincides with the R16 reported in the sketches found on the internet of this small hybrid control board (ok 27Kohm)At this point, let's leave my scheme aside and take into consideration that sketch found on the net (Polish? Czechoslovakian?), you can find it attached as a control schematic; attached I also have the sketch that I found on the internet, of the components of this board (attached control component).If we look at the I-sense signal that comes from TA1, it enters the control board from pin 3 (the 15 pins marked at the top in the sketch); it then arrives at C9 and passes through D1 (and up to this point it was ok even on my light blue diagram); but now a whole new world has opened up for us knowing that those resistors exist, in fact the signal as you can see from the sketch has R16 with the operational 2 of the LM324, and as you can see it also goes towards pin 3 of the TDA1060 passing through R8 and R6.So with the 3 attached sketches (control component, control schematic, control to main board) we can now think more concretely about how everything works.You had a great intuition, thanks.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 02:34:30 pm
content: I would then also consider R34, as you can see from my diagram it is connected to TA1 and the I_sense signal and should determine the output current. Measured connected to the circuit it is only 3 ohms, from the diagram it should be 39 ohms. As highlighted on the 'control to main board' sketch, they put an exclamation point of attention on this resistor, I think it is worth unsoldering a pin and measuring its resistance well!

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 02:50:33 pm
content: Now that we know that those green pads on the control board are real resistors, I have a doubt that I had noticed right away: a strange pad at the top of the hybrid control board not covered by lacquer like everything else, as if an SMD component had 'exploded'. Seeing that that track ended on these green pads that I thought were without resistance, I had not taken this silver spot into consideration, but now perhaps it would be a good idea to investigate further. What if it was a resistor (of the superficial type like the others) that exploded? Or any SMD component.Here is an enlargement of how it was originally, then I scratched to understand what was underneath, and I gave up because it ended on pads that I thought were empty, when instead we now know that they are superficial resistors.I indicated this missing part (maybe...) with the blue arrow, in a photo taken on the control board as soon as I opened the soldering iron. Looking at the 'control schematic', this missing part is on the trace from D1 to pin 3 of the TDA1060. I need to better understand if it is an exploded part, or if there was nothing there originally.

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 07:02:08 pm
content: the one on top might be a probe point for some kind of automated test system it is structured like the pins on the bottom. perhaps input for a test signal for manufacturing to measure board function.I think if you look at those resistors under a microscope, you might see the serpentine laser cut marks on the thick film?if you need to adjust that board, the control pins on the bottom might not be enough to perform all manufacturing adjustments, so they had to add one on top. each pad costs silver so they design it for the minimum amount.so the current sense pin goes into a diode to rectify, then some op amp and resistors to filter and amplify it, and the chip responds to a over current signal. I think the pen schematics you found work.the op amp and diode are the things most likely to break there. but yeah you can probe that pin to see if it looks like a realistic feedback signal or a false trigger. if its real it means you have a real short circuit

author: coppercone2
author_rank: Super Contributor
timestamp: September 08, 2024, 08:08:57 pm
content: alright and for those heavily soldered traces, the best tool is wickYou can get fairly thick wick on amazon or digikey, 4mm. It needs to be soaked in flux (like dip soaked) and then with a sufficiently powerful soldering iron you just wick it up. YOu might need alot but its cheap. The cheap wick especially needs to be soaked in flux, the flux it is provided with just does not do anything. like good rosin flux. Then you need to clean it up with alot of towels and flux remover.You can preheat or co-heat the board using a hot air gun or hot plate.A flux covered wick should remove all the solder. If its melting and not sucking it up (turning silver) the wick needs more flux or its oxidized. I like the premium brands because they wick faster personally. When its really tough and I got the hot wick pressed into a hot joint sometimes squrting flux on it from a bottle can help. Its a thermodynamics problem, this is where the 200W irons come in handy.For desoldering a heatsink it gets hairy, you might need to say preheat the oven, MEASURE THE TEMPERATURE to verify its not too hot, turn it off, put in the board and let the big board soak up heat for 10 min, then give it a shot for soldering.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 08, 2024, 11:39:03 pm
content: I checked the schematic on the sketch (yes I think these sketches are reliable), that silver spot is not any component but a test point evidently. Well, this means that no component has exploded.The small 3-pin SMS diode seems ok with diode test, while the opamp as you know is new (I changed the LM324 chip). I hope that the continuous short circuit does not damage further, but it is always next to the light bulb that dissipates that extra current.I will analyze this I_sense signal better, I can see it while I have no short (just raise the potentiometer to the max), and instead see what happens when I have the short. The problem is that with the short, any signal is always very wide/noisy, not easy to read.I unsolder R34 anyway, that resistor is important for the regulation of the output current and should be 39ohm.I put a microscope image of a resistor of the small control board, all of them have that black mark in the center of the resistance surface.To unsolder the components that have leads in common with the large tracks (for example in the image they are the pins of the large filter capacitor), ok as you say I could use the thick braid (I have them of all sizes/thicknesses, as you rightly said when I use them I always immerse them in flux. Another solution that came to mind, would be to cut around the pin with a diamond cutter of the dremel, separating the tin of the pin, from the tin of the large track, and then use the pump.

author: coppercone2
author_rank: Super Contributor
timestamp: September 09, 2024, 01:00:01 am
content: that is a suspicious mark, the reason why that resistor is there is because the current transformer makes a giant voltage unloaded, IIRCSo there was a event thereand fyi my miller won't even turn on. There is a 3906 I need to replace, it could be controlling the bigger parts, but i am seriously tired of it.i think i can fix it maybe if i take it easy because i am liable to say fuck it and really break something being negligent, its very irritating to even probe something on it right nowI am happy with the progress I am making with the electroplating, electroless plating and also thick film (kiln work), so there is not too much reason to be upset because of a bad welding machine, even if its tig. I thought those processes were totally outside of my capabilities but they offer more to electronics then welding can for what I am interested in.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 09, 2024, 03:09:10 am
content: I unsoldered R34 for the measurement, ok it is 39ohm. I also removed the capacitor C11 (the one that heats up only when there is a short circuit), ok as indicated on the diagram it measures 470pF.This C11 was soldered on two fairly large tracks, as mentioned before I first removed the tin with the dremel at 360° (you can see it in the photo below, especially on the lower pin), then ok with the pump it was unsoldered easily.I will continue to check suspicious components, so in the meantime I will also review the soldering.Don't give up on your Miller, but I would be curious to see the cleaning process you carried out. Update your topic, or even privately.

author: coppercone2
author_rank: Super Contributor
timestamp: September 09, 2024, 03:44:34 am
content: lol eventually, because last year I gooed this thing up etc, its difficult to even probe it. its extremely taxing to work on this machine.But I did do a good job, I checked many parts, replaced many parts... it makes me think that I might be able to fix it because I went through most of it before. But when you need to fix your OWN work then it really bugs me.These inverters are HORRIBLE from a 'cascade failure' prospective. its that one circuit thats like your mailbox getting rusty means your refrigerator is going to explode. I noticed the usual "keep it simple" type approach seems to fail me, there is so much interlinked stuff , I say its surgury, not repair, because you can really kill it instead of just making an isolated fault like most things in most processes.WELL I FOUND A BAD 2N3906 that I forgot to replace. That might control the whole power up circuit.Lol, usually when it won't turn on at all, its better then if it turns on and does not work. The goo shifted around during cleaning and made a mound near the transistor and I misssed ityou have no idea how badly I want to redesign parts of this machine to see if my ideas would work better and be more durableyou know I see things changing in the future, the PFC modules you can buy are almost there for a welding machine. That means you can use a commercial off the shelf part to basically replace a good part of their entire properietary card. Plus a few power supplies.I would make a rack mount franken tig using laboratory function generator, some modules, etc. I almost thing you can get rid of 1/2 of it. So long you can control that inverter card above the IGBT, the rest can probobly be replaced. But I do like the idea that you can move this unit out anywhere to do something, so I need to respect the portable nature of it. I am almost sure I can make a boat anchor that interfaces with their "welding subsystem", none the less its infuriating that what is giving me the problem is something like a low voltage power supply used to drive a relay and that fancy rectifier.And this machine is what gave me a "introduction to conformal coating" , all the conformal coating work really had quite a learning curve. I have been trying to do my repairs by 'dealing with it' locally, rather then removing all of it and giving it a honest restart, I was too excited to weld up all the coupons I got to do the right thing and remove it all, then reapply it, wash and bake out the boards, probe all the active components, etc. I really thought I could get it back and running like that week, which is something I am learning that you just can't do with this type of circuit... once it messes up, you gotta get NASA on its ass.

author: coppercone2
author_rank: Super Contributor
timestamp: September 09, 2024, 04:17:46 am
content: ok that dark mark might be the laser trimming process. They cut a L into it to increase the resistance.I did it once on a shunt I bought, by carving a serpentine square pattern on it with a milling machine, and had it hooked up to a mili ohm meter. I got it perfect, but there was ALOT of burrs because I had a shitty endmill. After the deburring, it was off... so I learned if you wanna mod a strip shunt, you do 85% of your work, get all the cuts you made perfect, and then you will probobly be at 95%.... then finish it with micro files.It turned out that all the burrs were actually significant to the total resistance of the circuit.The L-shape is the easiest and fastest, but there is alot of techniques that can effect the RF properties of the resistor, so it can be way more complicated, but for a simple welding machine circuit its fine to do it that way.https://laserod.com/capabilities/laser-resistor-trimming/

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 09, 2024, 08:17:31 am
content: Keep going with this Miller, she can't win. I wish I had found a transistor gone on mine (leaving aside the igbt, the transistors are only two on the main board, and a couple on the logic).I didn't know about these surface resistors before now, yes for all of them they used that L sign to adjust their nominal value.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 09, 2024, 05:34:21 pm
content: Pins 7 and 8 of the TDA1060 (rx and cx) determine the frequency of the internal sawtooth signal. The resistance on pin 7 is 5.8kohm (the specification goes from 5 to 40 kohm), and the ceramic smd capacitor should be 2.2nF (I can't measure it well on the circuit). This combination should give an almost maximum frequency to the wave, around 100Khz.I noticed that when I don't have a short (but in this case I don't have any output voltage from the soldering iron), if I measure pin 7 I don't detect any pin/tip contact problem on the multimeter. When there is a short (and in this case anyway the TDA has an output that turns on the IGBTs and therefore I have a soldering iron output voltage of 8 even if dirty), when I place the tip on pin 7 of the TDa I hear an unpleasant tick in the TDA1060. I don't understand why, the resistance is in the required range, the contacts are goodWhile pin 3 of the TDa (Feedback), has a constant voltage of about 3.6v, therefore being somehow connected also to the I_sense signal that comes from the current transformer TA1, I believe that signal does not detect problems. To inhibit the output of the wave from the TDA, the feedback pin should have a voltage lower than 600mV.I will continue to search for where this short circuit lies.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 10, 2024, 12:30:26 am
content: I have some interesting news: I had the board tilted at about 45% to facilitate the measurement of voltages on the small control board. Then I lowered it while still under voltage (perhaps placing it on the table it received a small blow, but not much); now while I have the short circuit with that tick, at the same time frequency of the tick, the relay continuously engages/disengages.And what if the relay was the problem with this short circuit?Even when it did not engage/disengage, I still noticed that it heated up to about 70°.In your opinion, looking at the diagram I attached, by unsoldering the relay from the board, can I try to bypass it for a few moments? Just to see if the short circuit disappears. Normally until now, when I increased the voltage with the variac, the relay enabled the contact around 120 vac. Thanks

author: coppercone2
author_rank: Super Contributor
timestamp: September 10, 2024, 01:55:55 am
content: that is a inrush limiter relay, it disconnects the resistors from the circuit after the main capacitor is charged.If you try to power the circuit through the 470 ohm resistors, and you try to weld with it, they will explode or something. I think it might be fine for a a while if you have no load on the circuit, if there is a short, and draws alot of current, it will get very very hotthe problem is the capacitor will draw maximum possible current from the outlet until its charged, and possibly trip a circuit breaker, and surge currents that stress your wiring and stuff.https://en.wikipedia.org/wiki/Inrush_current_limiterOn my machine, when the inrush relay was acting up, it was because the control board was messsed up with lots of bad chips

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 10, 2024, 03:03:26 am
content: I don't understand how it happened, I just lowered the board while it was under voltage. Of course it could be the signal that goes from the relay to pin 10 of the control board to trigger this Finder on/off. I wanted to do this test just to exclude the relay from the possible causes of the short circuit.Since the contact became NC at about 120v, I could also simulate it with a flying switch, but I would have to figure out how to connect the other two contacts (from the M10 pin and the 13.7 power supply).

author: coppercone2
author_rank: Super Contributor
timestamp: September 10, 2024, 03:14:33 am
content: something is cracked or loose, it must be sagging or flopping or tiltingbad contact is most likelyI bought more conformal coating remover after watching some videos of transistors burning out from over current through a microscope, some little valve is likely vaporized on my welder so its fixable. I was getting seriously over whelmed thinking about the problem, but when you see that its essentially replacing a fuse some where, it gave me some strengthIts the cost of doing business I guess, like having to remove nuclear waste or raking leaves.

author: DisasterNow
author_rank: Regular Contributor
timestamp: September 10, 2024, 09:59:38 am
content: But is it your circuit board in the photo?Yes, it could be a loose contact, in fact I was lowering it with the insulated handle of the screwdriver and when it took the small kickback resting on the table, the relay started this on/off. Maybe that short circuit increased and the control board inhibits and enables the relay continuously now. I want to understand how the relay engagement sequence occurred at startup, slowly increasing the voltage with the variac is easy to understand and then I want to try to make the contact of the relay manually with a switch at the right time, just to exclude that the relay could have problems (in addition I unsolder and re-solder it, which is not a bad thing).I also want to unsolder the two large filter electrolytics, and also measure their ESR, they are many years old (20?) and maybe they could be the cause of problems, who knows.Then I will seriously start to unsolder the power part, also because I was wrong, everything is inhibited if I have the potentiometer at minimum (not maximum as I had stated), and as soon as I increase the power, the short circuit appears at the same time that the control board enables the signal on the pulse transformer and consequently the IGBTs start to work and in fact with the short I start to have an output voltage.

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 02, 2024, 11:29:10 pm
content: Not finding a solution to find the short circuit on this welder, I decided to unsolder practically all the components (on the board at the moment only the current transformer remained, the power one and that's it).Then checking these components individually, I found nothing wrong.Having also removed the small logic board, I did some tests by powering it separately (on this board I had already changed the TDA1060 and the LM324).From the test performed (I also connected the potentiometer that I had unsoldered from the main board to the right pin of the logic board), I saw that as soon as I move the potentiometer from zero, ok it enables the signal output from pin 14 of the TDA1060 and it seems good, the signal then arrives at the IRF110 mosfet from where however it comes out of its drain with obvious spikes (as shown in the image below). The signal will then go to the pulse transformer, and subsequently to the IGBT gate.It seems to me that the output signal from the mosfet is not ideal with those spikes, even the amplitude seems reduced to me (from the TDA the signal comes out with an amplitude of 8v, from the irf110 the amplitude is 2.5v if we also calculate the spike). I could try to connect the pulse transformer downstream of the irf, as per the diagram (without load...), to see what signal comes out of its secondary (signal that would then go to the gates of the 8 igbt).

author: coppercone2
author_rank: Super Contributor
timestamp: October 02, 2024, 11:47:38 pm
content: that signal is shape probobly fine, IDK about the voltage levels, but the spikes looks like lead inductance or something. Its hard to probe a fast square wave.measure the voltage on the source though, what comes out of the transistor won't be more then what goes in, it just chops it

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 03, 2024, 12:02:05 am
content: the signal frequency is 85Khz (it is regulated by a resistor and a capacitor on two pins of the TDA1060). The signal is actually stable, only with the logic board I don't see any short circuit disturbance. I will also try to connect the small pulse transformer to this signal, as per the board (I also unsoldered that one).About 8v pulsating arrives at the gate of the mosfet because I shorted pin 10 of the TDa with the Vz pin (as suggested by the datasheet in case I didn't want to use a signal on pin 10); I didn't check the source, I'll try,I thought I would at least find where that short circuit came from, but nothing. Unless it comes from one of the 4 transformers...

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2024, 12:52:43 am
content: maybe its arcing in the transformer or something with bad lamination?

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 03, 2024, 01:54:29 am
content: Since all the components I checked on the bench seem to be ok, it could also be that the problem of the small short circuit is in one of the transformers.I have two of them here on the bench (the pulse one that I will connect to pins 13 and 14 of the logic for a check; then I have the one between the two rectifier bridges. The amperometric one and the power one are still on the board, I will unsolder those too.Only the 3 large heat sinks will remain on the board, I could also see what is under those too.

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2024, 02:30:20 am
content: did you try probing that signal with the spring ground on the oscilloscope?https://www.digikey.com/en/products/detail/teledyne-lecroy/PK007-016/4162625you can make it out of wire too

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 03, 2024, 06:33:22 am
content: I have the spring supplied, later I will try to check the output signal from the IRF110 again (the signal in the image is with the usual passive probe ground)

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 03, 2024, 03:19:19 pm
content: I also tried the irf output signal with the spring mass, a little better, but the spikes remain.I measured the signal better on this mosfet:. the signal on the source (in the logic board sketch they indicate it as gnd), is an alternating square wave signal, with a total amplitude of 100mV (frequency like that of the gate, 85khz); it does not present any anomaly, no spike.. the output signal from the drain, is a square wave but negative, with an amplitude of 500mV and an ok frequency of 85khz; here the spikes are evident (as you can see from the image), and measure about 1.2v above the signal. So the signal undergoes a 'degradation' passing through the S-D channel of the mosfet.Later I will try to connect the two logic outputs (M13 and M14, where the MOSFET signal comes out), to the pulse transformer (Tr4 in the schematic) to understand what I will have in output on the two secondaries, which in turn go to the 4+4 gates of the IGBTs.

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2024, 08:45:04 pm
content: I think for a fast switched signal, that actually looks pretty normal. I see similar when probing some switching supplies. It will look different under loadSwitching power supplies are often ugly. They clean up the output sometimes, i.e. for lab supplies, somewhat, but what is actually going on in the supply is often just bad. I think they sometimes even have circuits for just basically ignoring the first few percent of a wave (they just assume its good) because the rising edges can be really awful and cause errors in measurement and control. Like dead time or something.. edge blanking might be the term, because the noise right past the trigger point on the rising edge is just so awful its hard to make a control system that can tollerate it, so you just pretend its not there.There is a reason you need a linear regulator for a clean output supply (in the microvolts of noise), in a switching regulator that stuff gets through to the output and makes ripple and noise on your supposedly DC power supply output.And your basically seeing a big part of the reason why its so hard to make them not mess with radiosit might look better if you had a bare die that is wire bonded on your circuit board with better traces and stuff, but its really hard because that should be in the nano-seconds and your also looking at a open circuit condition!

author: coppercone2
author_rank: Super Contributor
timestamp: October 03, 2024, 08:54:09 pm
content: if you wanna see how things work with big nasty spikes like that, here is a starthttps://electronics.stackexchange.com/questions/585767/what-does-leading-edge-blanking-do-exactlythe electrical engineering equivalent of putting on black goggles for the nuclear flash or holding the telephone away from your face when you know its going to be bad, there is always that one caller you know that you know its better not to listen to the phone for 10 seconds before they wait a response after a statement of no meaning

author: DisasterNow
author_rank: Regular Contributor
timestamp: October 03, 2024, 09:39:13 pm
content: I agree, these peaks in output from the mosfet do not affect the failure of the welder. It was just a signal analysis out of curiosity. I have now removed all the components from the board, I do not think I will solder them again. My mission was only to find where that small short circuit was hiding that occasionally inhibited the tda1060 and in fact the current output to the electrode.This evening I also unsoldered the current transformer, my mission now is only to test the 3 transformers on the bench (the pulse one, the current one and the power one), then I can archive this chapter. Honestly I was confident of repairing the failure, it was not so, but I did not mind analyzing this circuit.