capturing voltage spike with fluke 289? - Page 1
Forum section: electronics / beginners

author: coppercone2
author_rank: Super Contributor
timestamp: May 30, 2022, 05:35:26 am
content: ###patient stabilized, diode no longer burning with capacitor replacement and variac input###So I have a diode that keeps blowing up and I am not sure if its over current or over voltage. I want to hook it up to a Fluke 289 to measure it. The common mode on the circuit is high and the nearby circuits are rather high voltage and it makes me nervous using any other equipment around it.The diode is a regulator diode followed by a switching transformer that provides 3 isolated rails on a welder for IGBT control. Circuit is Clamp diode + zener diode + 100nF capacitor to power IGBT driver in isolation.Not too sure what mode I should use to try to capture a spike.. normally I would use a scope meter but mine is totally SOL. Will doing AC peak detect or DC peak detect make more sense? The diode goes short circuit very quickly. Not really even sure if a DMM is applicable to this situation.. Anyway I want to learn if I can use this meter to trouble shoot real dodgy shit like this with greater safety. It does not need to be too accurate, its just for repair diagnostics. Weird noise and over-heat flux smoke within 2 seconds of power up and it reads dead short. I wanted to get it right first try because I am tired of resoldering a diode on every power up.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 30, 2022, 11:11:34 am
content: If the diode shorted I think you have over voltage. Make DC voltage measurement across the diode using peak min/max mode.

author: coppercone2
author_rank: Super Contributor
timestamp: May 30, 2022, 06:19:30 pm
content: Ok, that was my first guess, but its good to be sure because I am sure that the less I have to deal with this the better. I though DC might have some kind of digital filter on it or something that might cause a problem.

author: bdunham7
author_rank: Super Contributor
timestamp: May 30, 2022, 07:06:16 pm
content: What diode is it and what voltage does the circuit run at normally? I would expect that the first step would be to put in higher voltage diode, and then when you've worked your way up to a 1N4007 (or whatever) then you aren't going to want to connect a DMM to a circuit that is blowing a 1kV rated diode. So you need high voltage probe. I don't know if the DMM is going to catch your spikes either---the F289 peak detection mode is good for 250µs.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 30, 2022, 08:04:55 pm
content: Quote from: coppercone2 on May 30, 2022, 06:19:30 pmNo it can capture a peak voltage of 250microsecond. Make sure it's peak mode and not regular Min/Max because that can only capture 100 milisecond values. You should also put the meter in manual ranging and set the range for the voltage you expect to see. Othewise it locks into the range when you switch Peak mode on and that could be a range too low to catch the peak.If set the meter for DC voltage measurement. Go into menue and select Peak put the probes into a 120VAC outlet I would get a Max of about 170V an Average of 0 and a Min of -170V.

author: coppercone2
author_rank: Super Contributor
timestamp: May 30, 2022, 09:40:49 pm
content: actually this might be necessary, it looks like when I replaced the IGBT the diodes are blowing one by one. I replaced glass diodes that were blown with ceramic diodes that were rusty and I think maybe the rusty diodes are just bad and replacing the IGBT made the diodes stop blowing but the last shady diode is still in there, in an hour when it has some time to rest ima replace the last diode with a digikey glass diode and maybe it will work. if it keeps blowing the new diodes Ima try the meter outso basically 3 diodes were replaced, the same one kept blowing, when I replace the IGBT the other diodes start blowing, which were shitty ceramic. I replaced 2/3 and they both work, so the last old diode is (blown) in circuit, and the front panel display changed to show 0V instead of 243V. So when the third diode is replaced it will be interesting to see what happens. perhaps it will work or they will all blow up and destroy the welder but I am gonna risk it. I thought ceramic diodes would be better then glass but who the hell knows what kind of shady bs I got on ebay. I also put the 1.3W diodes instead of the 1W diodes. I don't know what was there originally because I just found a fragment of glass stuck to adhesive

author: coppercone2
author_rank: Super Contributor
timestamp: May 30, 2022, 11:52:18 pm
content: you know what fuck millers bullshit power distribution 'topology' I don't even want to trouble shoot, I am gonna power those things from batteries and see what happens, fuck those multi phase bullshits or whatever they are. cascade failure waiting to happen

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2022, 01:01:23 am
content: and my leading theory is that the poorly labeled transformer has internal leakage that is shorting the diode. I think the oscillator sounds like its running correctly and I recall once the diodes blew when it was not connected to load (I was still not sure at the time). I think the other signs of arcing on the PCB can be explained by punch through occuring at the transformer between primary and secondary. I suppose I should desolder and test it, but I hope I can disable that entire section and run it on batteries because I am sick of undoing all those lugs and boltsbut I will do one vmax test for fun, i got those dioddes on binding posts right now so its easier to replace lol

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2022, 02:27:38 am
content: well OK, the max voltage (I set the meter for 500V range) on the PEAK mode says 30V, and it drops rapidly. Is this too much maybe? For a no feedback supply I almost think this is normal but I am not sure.fuck it, I am just gonna put a bigger wattage diode first before more fucking around, I forgot my reasoning behind choosing the 1W diode. I think the fragments of glass I recovered brought to mind a 20V diode that I knew about but I guess 2/4 digits (really 1 digit because the last one was a little ambigous) is a shot in the dark based on manual voltage.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 31, 2022, 12:18:05 pm
content: 30V across the diode in the forward or reverse direction? If it's reverse direction it's not too high for most diodes. If it's in forward direction then a lot of current is going thru it. Is the bad diode shorted or open?

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2022, 01:25:00 pm
content: the diode is a regulator and it failed shorted. I am measuring directly across the regulator diodeAgain it might be too fast a pulse but it also might just be the wrong diode. I figured it was 1Watt but I am thinking that maybe IGBT driver supply needs more then 1 watt. The parts that were there disintegrated while I was trying to remove the glue and the size of various diodes is very similar. Thinking about it, the new diode i put is maybe little smaller then the old diode.I am kind of thinking based on my IGBT driver designs that I kinda messed around with a little, 1W is a little low for a supply, and I noticed when I put 1.3W instead of 1.0W diodes, they lasted a little longer. I figure somthing this big wants like 2W at least. They had glass diodes so I don't think it goes above 3W but I bought some 5W diodes to wire in on posts if I have to incase it was some weird unobtanium diodes there. The 5W might actually fit on the PCB ok.

author: bdunham7
author_rank: Super Contributor
timestamp: May 31, 2022, 02:50:50 pm
content: OK, it is a zener diode? Then the issue is most certainly too much current, so you should measure that. It would take an extreme transient to damage a zener, although your welder is one of the few places where you just might find one. Perhaps the current-limiting resistor or circuit has shifted in some way with age so that a marginal design has now become faulty. There are also 5W zeners, 1N5363B--just note that higher wattage parts still generate just as much heat as smaller ones so in a confined space a higher rating won't always eliminate overheating.

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2022, 03:07:50 pm
content: It was like potted so it can probably handle more steady state current and the pcb was a little discolored but I killed out most of the sections that were bad and fixed it up. Yeah now I’m remembering the diode I got as a replacement seemed a bit small compared to the disintegrating ones. Probably should measure current, just has a trollex connector so it’s a hassle … but I suppose it’s time to get medieval on it

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 08:09:46 pm
content: well I tried a 5W zener and it smoked that too.The thing is, I don't see any resistors on the output of the transformer. Is it possible that there is a current limiting resistor on the input to the 3 winding transformer that powers the zener diodes that shorted out and its just not current limiting? I am not used to switching supplies, I assume they might current limit the whole transformer at the input rather then current limit the output of each transformer winding.If that resistor was gone, it would smoke any diode, since its connected a ultra low impedance it looks like (I think its rectified mains on the input).Since it smoked the little diode when the load was disconnected, and it smoked the big diode when the load was connected, I assume it is a good indicator that its not a downstream but up stream problem. Must be one of those fucking silicone coated rubber resistors. Hard to read those bastards when they put varnish on top.time to work on 'bishop'. Yay I get to try to read a label on some gummy shit covering some burned shit that is again covered with some other kind of gummy shit. What the fuck happened to ceramics god damn, electronics turned into gumby. when is miller electric releasing their gynoids?

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 09:39:55 pm
content: well nope, I desoldered those resistors and they check out OK. It seems like every fucking part near the transformer is OK. I don't know how it keeps blowing diodes, I replaced all 3 with 5W ones that bearly fit on the circuit.I wonder if one of the resistors that was a little charred nearby has carbon inside that is arcing over at high voltages but measuring within spec on DMM. I don't know if I should start removing parts and testing them 1 by 1 on a HV power supply or what.Have you guys seen stuff that measured totally fine within like 1% or 5% and had a arcing problem?I am starting to think there is some kind of voltage spike going on that the DMM can't capture. I just don't know what will happen if I ground one of the isolated IGBT driver supplies with a oscilloscope.. I am almost thinking about just getting some more shit for acetylene and forgetting this whole TIG welding thing because this seems way too fucking fragile. I suppose I can desolder some parts and test with HV but I am seriously losing hope here.Could there be something wrong with the transformer? I read that the cores can crack or something like this, it looks fine cosmetically and the windings seem fine.

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 09:55:18 pm
content: And BTW the middle zener diode fried this time, I replaced all 3 1W diodes with 5W diodes. Its random which diode breaks. There are two resistors infront of the transformer that are within band codes, and some beefy diodes that all measure OK. I think this has something to do with the 800V and soot or whatever.. I really feel like I would have found a faulty part by now, from experience. This feels like a new problem .When I hooked up the PCB that its connected to without IGBT it measured about 3mA consumption per 20V rail. The ebay pics of the board show little diodes, I think they were infact 1W diodes originally. I will desolder some power 150Khm resistors that meausred fine and measure the PCB with a HV power supply, in an area that I cleaned up from soot using rubberized abrasives. Maybe its not clean for the HV found in the instrument, but I will say on some other power electronics I worked on, mildly scraping the soot off with a pick (where it still looked shitty) was enough to break the carbon short, I feel like my job was over kill already but who knows.

author: bdunham7
author_rank: Super Contributor
timestamp: June 03, 2022, 10:29:15 pm
content: Maybe take the time to sketch out the circuit as best you can and post it so we can have a look.

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 10:30:21 pm
content: Ok, the plastic film under the PCB has two holes that are blown right through it (fairly thick plastic sheet) under where the diode is. I wonder what voltage level it took to make those holes (and crack the input rectifier brick).I think there is some kind of problem with the substrate to be honest. I see similar pictures online near the 150K resistors being burnt.If it punched 2 holes in the plastic film under the welder I assume that might be enough to fuck up the substrate?

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 10:45:17 pm
content: ok reverse engineering is gonna take a while because it means i need to remove the backplane board and undo a bunch of lug connectors and shit. If i try that right now I will end up smashing it into the wall, the sheer cost of the object is the only thing keeping it alive right now. There is some serious bullshit going on here because there are like no success stories about this welding machine, they replaced the PCB with a different version too, there is probobly some insidious shit going on. I want to smash it with a sledge lolI will try to see where I can disconnect that whole section and plug it into 3x 20V linear supplies. I am not working on it any more until I can prove its not two problems interacting with each other on different circit boards

author: bdunham7
author_rank: Super Contributor
timestamp: June 03, 2022, 11:29:26 pm
content: Quote from: coppercone2 on June 03, 2022, 10:30:21 pmI said:QuoteAnd I think that might just qualify as 'extreme'...

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2022, 11:36:23 pm
content: I have an idea too, to use a LCR meter to measure the resistance from the last transistor in the circuit to the input of the transformer to see what kind of impedance that has. Maybe it will find lack of impedance. But I really think it might be some unwanted path that developed from HV stuff. I think maybe those big boy capacitors have a path to the diodes some howI don't know how to find it besides depopulating the whole board and testing it with like 1kV to find leakage

author: BeBuLamar
author_rank: Super Contributor
timestamp: June 03, 2022, 11:52:56 pm
content: You are talking smoke then it's not overvoltage but rather over currennt. You said the diode shorted buy if it smokes it would be open afterward not shorted. If you have 30V reverse bias it's no problem because diodes are rated 50V at least. However, if you measured 30V in the forward bias direction that's a lot of current is going thru the diode as normally you will have only about 0.7V in the forward bias direction.

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2022, 01:04:32 am
content: The zener diode is reversed biased I think, if that is the notation used to describe a diode making a positive voltage rail. So the voltage peak max on the 289 DMM is 30V and it drops down to 20V. I noticed this because the diode I was measuring was NOT the one that burned up at the time.So primary : 3x secondary with 1x diode on each. At start up one of the diodes will at random burn up and then the other two sit at 20V while the big cylinder inductor on the corner of the PCB makes a buzzing noise. I think that the shorted diode on the secondary acts as a current limiter because of the big load dropping the primary voltage or something lol?.When the test is done one of the diodes is always reading a dead short, as soon as I clip it from the circuit the MUR120 reads the normal voltage drop again (the circuit has a MUR120 and a 20V zener together with a 100nF capacitor. The capacitor and MUR120 are fine. The diode remains short the month after I clip it off from PCB (I have a pile of them now).On the primary side of the transformer there is a 1500Ohm resistor and some other resistor that reads in specification. Upstream there is a IGBT or FET with a diode that I also replaced. Upstream of that is a IGBT or SCR (bigger package) that is next to 4x 150Kohm resistors that have burn marks on the PCB but measure fine when desoldered. I cleaned up this area using abrasive when they were all desoldered.I have not powered up the PCB without either shorted or fresh diodes because I am worried it will destroy the IGBT control board attached by the cable harness.There was some browning from the big capacitors on the varnish that was peeled off.. dmm does not detect short to any adjacent path.Each of the loads for the 20V rails was measured independantly with a power supply and they draw less then 10mA, but the IGBT is not connected to the board. I replaced the big IGBT and checked all the big power diodes nearby and there are no problems there. At one time I forgot to connect the load cable to the PCB with fresh diodes and the diodes also burned up with no load connected.Since all the resistors nearby read fine, I think the only explanation is that there is some leakage going into the circuit? I am going to find the output of the last driver thing on the PCB and see if I can measure AC impedance to the input of the transformer through the whole circuit path... if I know the resistance then I can measure the AC voltage on the primary with a scope that is properly connected on power up and see if there is excessive voltage there considering the impedance is known, rather then trying to measure the isolated secondary, and make the assumption that the diodes should be running at 1-3 W (since the 5W diode is clearly much bigger then what was there originally). I can use the HV scope probe for this.

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2022, 02:05:21 am
content: Hmm there is a LEM HY-25P on the PCB, looks like a current sensor. I wonder if this is bad can it have some monster inrush or something that takes out the circuits some howCould this be a inrush control relay issue? I wonder if they use that technology, there is a relay here for some reason on the main boardI wonder if it could be that the filter caps are too much a load because of low ESR that they pull too much current because some kind of soft start routine is being ignored. I mean you figure that would be done locally but maybe its causing some sort of problem. I held the board under light for a while and I just don't see any thing suspiciousI wonder what would happen if i just add series resistance to the transformer primary lolWhat I am saying is that maybe the design is not short circuit proof so they make slow start to protect it and when that goes out there are problems. Maybe its to keep heat down or efficency up?I could remove the filter caps and see what happens. Or its possible one of the cards has a leakage issue that is frying it from the other end. the two cards are a probelm. But the 20V rails are totally isolated, so I don't think its the cards because I suspect stuff would be blazing hot/smoking on them if that were the case. I wonder what will happen if I disconnect the load and desolder the 20V isolated filter caps that are possibly a dead short on fast start up.....

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2022, 04:42:59 am
content: well I started to trace out the transformer primary, it looks like there is no series resistor anywhere.It goes from semikron igbt brick thing to 35V capacitor to heat sinked diode to 1mH inductor that goes to one side of the transformerthe transformer has a 10nF foil across it along with a flyback diodethe other side goes to a IRF640 middle pin (so its like a low side driver? , makes sense if capacitor is on high side), then the source of that goes to 2 0.5 ohm resistors that are in spec, which are in parallel to provide 0.25ohms of ESR and that goes to other semikron igbt pin. the middle pin is also connected to some transistor by 7.5 kOhm.the coil resistance is 0.219 Ohm, the resistors are 0.25Ohm, and it has all the traces, and the diode is in series with it so it does some voltage drop.So the ESR of the switched loop is 0.5 ohm + trace + diode + IGBT.and the transformer is really low value, with kelvin I measure 12 miliohms (not sure if this makes sense, but i guess its high frequency)so what does the 0.5 ohm esr (seems to be by design) and 12 miliohm transformer winding say? i get 50 amps. ??im not exactly sure whats wrong but i imagine if this is being chopped at the wrong frequency and it depends on that inductor for resistance maybe something really bad is happening? i am gonna draw it on paper later to see if i missed some other path or something lolactually the transformer is connected to common on one side (on a pcb) through the inductor 1mH and the series resistance is 0.25 ohm + igbt + transformer + inductor and the diode is like recycling? or whatever, and there are some passives branching off through it. (diode and the non common side are connected directly to SKiiP module).

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2022, 07:15:09 am
content: I think this has something to do with the control regulator on a daughter card not working, maybe something with fold back. That card was severely damaged and I thought I fixed it, but i guess not. That was too hard to trouble shoot. please don't bother with this thread because I don't even want to look at that card anymore, maybe next year. I am putting this away into the attic so I don't waste my summer, it has like 50000 HV mosfets on it and can get fucked

author: BeBuLamar
author_rank: Super Contributor
timestamp: June 04, 2022, 11:06:32 am
content: I didn't know that the diodes were Zeners. If so what's their breakdown voltage?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: June 04, 2022, 05:43:08 pm
content: Coppercone2, This board that has the diodes that are burning up,...can you purchase a new board from Miller Welding? At the very least you can use the new board to troubleshoot the bad one. The welder is of no use to anyone in it's present conditionand just putting it out of sight is just going to prolong the inevitable. I've been down similar roads before, so I speak from experience. Best of luck.

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2022, 06:46:22 pm
content: the problem is the boards are like 1.5k each lolif I took time to replace every single part in this it might be cheaper. But the other problem is I don't have the tig torch or foot pedal or anything, so its not even appealing. My budget on this thing is basically tapped out, and I don't think I like flyback supplies or stuff powered directly from mains, and I already had a year a while back that I ruined trying to fix some expensive equipment, do not want a repeat of that summer. Tig welding is not what I want to get into with the economy in this state.. huge investment.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: June 05, 2022, 04:42:45 pm
content: WOW, I didn't know this was a big bucks unit. My only suggestion now is to look around for a welding forum, and pick some brains there. I wish you success.

author: coppercone2
author_rank: Super Contributor
timestamp: June 05, 2022, 04:50:29 pm
content: I am gonna try one more time because I don't know if I ever really washed the PCB good because I just assumed the varnish was good. I left them all in ultrasonic for 30 minutes and some of the conformal coating did peel off, that had a slight mustard color near the main voltage bus. I wonder if there was leakage into the control circuit for a duty cycle voltage adjustment that was messing with it. But I realllly want to put it into the attic because its draining my money patience and time, but I can't resist.One thing I forgot to check is if there was soot under the connector plastic housing... i would kick myself if its something dumb like that, but they use headers for 800VDC!TBH if I buy a isolated high voltage differential probe, my tune might change. I could solder in DIP socket connectors to the diodes, buy a cheap string of diodes to replace and take oscilloscope captures at the gate of the different power transistors, but I got a really strong feeling that I was wasting my time and learning nothingAnd this might have to do with a complicated power factor correction circuit, I think it might be failing to do something like active spike filtering or whatever (where it disables a transistor when they know there will be a spike on the circuit)

author: coppercone2
author_rank: Super Contributor
timestamp: June 05, 2022, 08:33:23 pm
content: oh boy I think I found a bad 100nF capacitor connected to the resistor from the V+ bus. When I was removing it, the end came off, with one end stuck into the PCB.I stuck one probe on the other lead and one probe into the hole that was left behind, it read 60Kohm. I was desoldering the other side and managed to break the capacitor off and it fell into a bunch of rubbish on the floor, and I found a too much garbage while sweeping so I just vacuumed the area and threw it away.I was not sure if this was from damage, but the capacitor came apart awfully easily. I got a very similar 100nF capcitor from my components storage box, and it took about 3x more force to remove the lead, and the lead broke off leaving the capacitor intact, without ripping the outer hull of the capacitor (i.e. it turns into a SMD part rather then getting structural damage with a big crater). I think that capacitor was damaged, I don't take the multimeter reading to heart because I could have damaged it poking it in there, but what I do notice is that it was too fragile.So maybe there is hope yet. I can't get away from this thing lol. I notice when parts come apart too easily that might mean fracture damage.

author: coppercone2
author_rank: Super Contributor
timestamp: June 06, 2022, 01:31:19 am
content: I managed to get it stable after replacing the suspicious 100nF capacitor. I also started it from a 20A variac set to 110V, when I raised the voltage to 119V it was still OK. Did not run it directly from mains yet.I need to do a thermograph to see if its not over heating, the diodes are at 18.5V now, and the inductor is making a slowly up-down ramping in intensity buzz. Display code -5, which is HLP-5 (missing letters), which is something with thermistor.Once I verify nothing is burning with thermal camera, I will look at the thermistor circuit and check the thermistor for damage.now that its not smouldering or making the bad noise I can work on it, check supply rails, etc.Put out fires and wait for the 6th ☑

author: coppercone2
author_rank: Super Contributor
timestamp: June 06, 2022, 02:33:48 am
content: First order of buisness will be to replace the 20V zeners with 22V Zeners as I originally thought they were. Since I measure 18V, it must be that the designer used 22V for whatever reason to get 20V output. Part of the reason I thought something was going on with the part, since the glass fragment I recovered was a 22v zener designation. So 3W 22V zeners should be correct.