Philips PM3212 Oscilloscope channel A problem - Page 1
Forum section: electronics / repair

author: Basileus
author_rank: Regular Contributor
timestamp: December 08, 2016, 05:46:31 pm
content: Current Status:SLOW(Im having exams at the university)Channel A trace is still way too high and cant be lowered. Amplitude seems wrong beyond calibration too.The problem doesnt seem stable. After fiddling inside the scope, the trace is even higher than before. I can see something only when i try to see the CAL signal and set amplitude ratio to 50 mV/div. By lowering the position as much as i can, i can see the bottom part of the square wave.<-This happens because of poor connection of the y pos pot. I reseated the connector and the situation improved. Still, trace too high and amplitude too low.I'm waiting for another scope to arrive, a Tek 2215, to keep troubleshooting the Philips PM3212.Project is currently on hold.Got the new scope! Love it.Original postHi!A recently got my first scope, a Philips 3212. The conditions werent specified by the ebay seller i got it from, there was only written "switches and potentiometers need cleaning".From milking the front panel i found out:The B channel works fine, amplitude works fine, focus and intensity controls work and the trace is nice and stable.OUTDATEDThe problem is with channel A. I had a trace on first power up, but some time after it totally disappeared. It appeared a second time after a lot of fruitless troubleshooting and the y position looked like out of cal. I mean, i wasnt able to move the trace down enough: with the y pos control at minimum the trace was still in the upper half of the screen. I tried to display the 1.2Vpp cal signal and the trace amplitude displayed was wrong: 1.1v. Tried with channel B, it works perfectly. After a short period of time, there was no trace on channel A. Again.PLAYLIST OF ALL VIDEOS I MADE ABOUT THIS OSCILLOSCOPE FAULTS:https://www.youtube.com/playlist?list=PLIgTdpoYMz1MnNDh-Nt9bgHrnhoELMqr6UPDATE 1:Right after writing this post i turned on the scope and.. BANG! there is a trace. Cant lower it much though. Still, i got it on cameraand i'm uploading a short video of the fault on youtube. Coming soon.UPDATE 2:-Tried to adjust DC balance trimmer pot, the situation improved a bit. Still way too high though.Maybe the trimmer pot is faulty.wrong. Trimmer pot values are within tolerances.UPDATE 3:After cleaning with lots of contact cleaner, channel B trace is unstable too.Probably oldway is right about weary contacts. You can tell how clicky-er is the mtb range switch compared to the v/div switches of the channels.Seems like the faults on both channels have similar effects, but different causes.Channel B is influenced by the ground coupling. Sometimes, the trace is perfectly fine; After you select ground coupling there is no flat trace, but a distorted, lower in amplitude square wave that goes away with a bit of wiggling of the switch.Update -> Same thing happens when toggling ac/dc couplingChannel A is similar, but gnd coupling seems to work fine.Seems like i've to disassemble the front panel. Again.UPDATE 4:Cleaned rotary switches with pencil rubber and lots of patience. The coupling switches made the trace unstable when wiggled. Hopefully, spraying lots of cc in them and pushing the buttons a couple million times did the trick.UPDATE 5:Trace on A is unstable again. Probably wear of the contacts. The cc magic has worn off. Hopefully, if the switch is kept centered, the trace is stable. Still a bit dodgy though.UPDATE 6:Found the channel A problem: transistor V509. I cant tell what is going on, it seems fine. Swapped it temporary with V511. Roughly adjusted channal A balance. Now channel A is fine.Other lesser problems- Invert channel B doesnt work properly, some times it works some times it doesnt. From playing with the switch i think its a mechanical problem. Since its a low priority problem, i'll deal with it in another moment.SOLVED, YAY! (the plastic cylinder inside the switch was cracked, i glued it to the pot shaft and reassembled it. In 2 hours. Those flying springs are a pain.)UpdateNow the switch x10 mag feels sticky too.. I'll probably have to repair it tooAfter i replace the reed contact, i'll know if i have to. UPDATE I replaced the reed contact. Took me 4 tries but im satisfied of how i soldered it. Yes, the switch doesnt do anything.. Time to pull out the front panel.. AGAIN..- The x10 switch for mag on the time base doesnt seems to work. Low priority fault.FAULT LOCALIZED, ITS THE RELAY THAT DOESNT SWITCH. Replacement is coming. In 2 months.-One illumination bulb has failed. I'll probably look for a replacement or replace both bulbs with LEDs.LED SYSTEM INCOMING! when i have time...Done. Now there are 4 red leds (2 over and two under the crt) that illumi ate the graticule. Sexy.Some pics of the new illumination system:http://imgur.com/a/0FYc3

author: LaserSteve
author_rank: Super Contributor
timestamp: December 08, 2016, 06:11:19 pm
content: I had one for 15 years. Take the time to fix it, you could not ask for a better beginner's analog scope.No promises, but I think I might still have the whole manual with troubleshooting guide. I'll look.Steve

author: dan3460
author_rank: Frequent Contributor
timestamp: December 08, 2016, 06:59:14 pm
content: Welcome to the board, first thing here is a copy of the manualhttps://doc.xdevs.com/doc/PHILIPS/PHILIPS%20PM3212%20Instruction.pdfI'm guessing that you do not have another scope. If you look in page 66 there is a block diagram of vertical system. You are loosing the ability to move the trace somewhere between the Pre-Amp and the switching amplifier. On page 68 there is a note saying that the balance can be adjusted by messing with R674. Maybe that can move the trace down.As per not getting a full signal display, you need to fix the positioning part first, then it should be a calibration procedure somewhere in the manual.You didn't said if you have a way to generate signals, you will need this to calibrate the scope. If you do not have anything like that you can use a know source of voltage (such a battery) to get a close enough calibration.Good luck.

author: Basileus
author_rank: Regular Contributor
timestamp: December 08, 2016, 07:19:42 pm
content: Quote from: dan3460 on December 08, 2016, 06:59:14 pmR674 is related to channel B "Shift balance channel B". The problem is on channel A, do you really mean R674 or R574, his channel A counterpart?No, unfortunately i dont have a function generator i can use to cal the scope.PS I adjusted R574, things improved a bit but its not enough. In the lowest position the trace sits half division over the middle line.

author: dan3460
author_rank: Frequent Contributor
timestamp: December 09, 2016, 01:16:20 pm
content: You are correct, I was looking at channel B, both channels are virtually identical. I hope you have DMM. You need to start checking voltages and resistor values. I have never worked on a Phillips before, but the schematics have a lot of voltage references that can be tested.For example look for R573 you should have -12V on one side and -5.8V on the other. Check the resistance across R2 (position knob) if is not easily accessible, you can find R571 and r572 and check it there. Check the voltages around V518 and V519, varying the knob position. The voltage at the base of both transistors should be -9V (if I read the schematics correctly).It is possible that one of those transistors around that circuit, V513, V514, V524, V526, V518 and V519 is bad, the good news is that all of them are available and cheap.You are going to have to measure parts, measure more parts until you find the one that is faulting. Also, by using the diode function you can check the transistors, in most cases, sometimes you can get a bad reading but that tis because is in circuit. The only way to really check is by lifting one leg of the part out of the circuit. Look in google how to use the diode setting to check transistors.

author: Basileus
author_rank: Regular Contributor
timestamp: December 09, 2016, 02:20:43 pm
content: Quote from: dan3460 on December 09, 2016, 01:16:20 pmYes i do have a DMM.Here are my readings:R573 voltagesSide 1: -11.90vSide 2: Ranging from -5.48v in the lowest and highest positions of R2, -5.87v with R2 in his center position.R2 resistanceI unplugged his connector and measured his resistance directly. Checking both paths from wipers to the other two terminals, resistance varies from about 50 ohms to 1050 ohms. Seems good.Voltage between V518 and V519 bases is -2.98v, doesnt vary at all by manipulating R2.I checked V513, V514, V524, V526, V518 and V519. They all give reasonable readings.

author: dan3460
author_rank: Frequent Contributor
timestamp: December 09, 2016, 03:20:05 pm
content: ok, here is something to investigate. The voltage at the bases of V518 and V519 should not change by moving the knob, that voltage is set by a voltage divider R569 and R568 and if my numbers are right (R569 59k, R568 178k) it should be -9V. Check the junction of R669 and R668 and see the voltage there. If different check the resistance of R569 and R568.

author: Basileus
author_rank: Regular Contributor
timestamp: December 09, 2016, 04:19:24 pm
content: Quote from: dan3460 on December 09, 2016, 03:20:05 pmVoltage between V518 and V519 bases changed to -4.77v, stable. Similar voltage reading between V618 and V619 bases on channel B.I just realized that right after turning the scope on, the A channel trace starts to shake and slowly climbs up by a bit. I'll leave the scope off for a bit and see if i can catch it on video.UpdateTurned it on again. voltages are back to -2.98v on both channels, exact same values. I think that the supposed dc voltage on the manual is -3v (not sure, the pdf is pretty low resolution and its difficult to tell). And yes, the trace climbs up a bit on warm up. Cant say if its relevant though.

author: dan3460
author_rank: Frequent Contributor
timestamp: December 09, 2016, 08:00:24 pm
content: I made a quick simulation of the circuit, bases of V518 and 519 should be around -3V so your -2.98 maybe is correct. Does the trace starts in the middle of the screen and then goes up? You didn't say if you have checked the resistors around V518-519 - 513-514 - 524-526.

author: Basileus
author_rank: Regular Contributor
timestamp: December 09, 2016, 08:06:57 pm
content: Quote from: dan3460 on December 09, 2016, 08:00:24 pmYes i did test them with the diode mode on my DMM, havent desoldered any (V524 and V526 are socketed). They seem fine.I'll record the next power up and post it.UpdateRecorded another power up, this time the trace didnt climb up nearly at all, 1/4 of div at best.Still, i'm uploading another video of the oscilloscope displaying the cal signal. Trace on A is quite distorted and his amplitude is unstable when using the v/div knob.

author: Basileus
author_rank: Regular Contributor
timestamp: December 09, 2016, 08:44:22 pm
content: Here.https://youtu.be/wjVrUPN72Dc

author: oldway
author_rank: Super Contributor
timestamp: December 10, 2016, 10:55:10 am
content: Your oscilloscope appears to have 2 different failures on channel A- wear of the range switch ... it is indeed wear and not a simple oxidation of the contacts because the oxidation occurs on the contacts that are not used.In a low bandwidth oscilloscope that is normally used for hobby, diagnosis and repair, channel A only is used in 80% of cases and channels A and B simultaneously in 20% of cases.The range switch of channel A is therefore always much more worn than that of channel BThe contact cleaner spray will not solve this problem, at most it will improve the contacts temporarilyThe real solution is to replace the A channel range switch with another in good condition.What I have often done is exchange the ranges switches between channels A and B, but it's a heavy job- There is also another fault in channel A: the symmetrical preamplifier does not seem to be balanced, so that the position potentiometer does not allow the trace to be centered.All this seems to me a repair which is not worth it.I recomend you to use only channel B.

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 11:41:17 am
content: Quote from: oldway on December 10, 2016, 10:55:10 amI guess i'll repair what i can and leave channel A be.It's really sad. I guess that if someday i'll stumble in another broken oscilloscope i'll get another range switch.I realized there is another problem. The pull for x10 mag for the time base doesnt seem to do anything at all. I checked the switch behind the x pos pot but it seems fine. Maybe the fault is in the main board connection or in the related circuit.

author: oldway
author_rank: Super Contributor
timestamp: December 10, 2016, 12:00:10 pm
content: QuoteCheck relay K140? (late digit not readable on schematics) for bad contact or open spool.Check resistance of x10 gain pot. (R1419) ...must be lower than 100R

author: dan3460
author_rank: Frequent Contributor
timestamp: December 10, 2016, 02:09:45 pm
content: That video gives a better idea of what the problem is. Did you use deoxit or similar product to clean the switches? I would give that a try.

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 04:14:19 pm
content: Quote from: dan3460 on December 10, 2016, 02:09:45 pmI currently have the front panel completely disassembled, it took me 2 hours of work to repair the invert channel B switch. The plastic cilinder inside the switch was cracked and slided on the pot shaft. Luckily it seems like its a common problem and following these instructions did the trick:http://siber-sonic.com/electronics/PM3214fix.htmlI used dry contact cleaner on all switches and pots(without dissasembling them).Now i'm currently mounting back the front panel controls. After this is done i'll check if i messed something up, if channel A trace stability improvedand ill do what oldway suggested to troubleshoot the x10 mag switch.I'm also planning to replace the illumination lightbulbs with 4 red LEDs copying the circuit shown in this repair video:

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 05:45:18 pm
content: UpdateNow the invert channel B switch works like a charm.But after cleaning with lots of contact cleaner, channel B trace is unstable too.Probably oldway is right. You can tell how clicky-er is the mtb range switch compared to the v/div switches of the channels.Wait...Seems like the faults on both channels have similar effects, but different causes.Channel B is influenced by the ground coupling. Sometimes, the trace is perfectly fine; After you select ground coupling there is no flat trace, but a distorted, lower in amplitude square wave that goes away with a bit of wiggling of the switch.Update -> Same thing happens when toggling ac/dc couplingChannel A is similar, but gnd coupling seems to work fine.Posting a video about it.https://youtu.be/YN70fz6rqN4

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 06:35:08 pm
content: Quote from: oldway on December 10, 2016, 12:00:10 pmI don't know how its inside that relay, but i compared it to the other relays, and i noticed that the leads going in the center of the coil are open circuit, while the others arent.

author: dan3460
author_rank: Frequent Contributor
timestamp: December 10, 2016, 07:20:29 pm
content: For what I can see on the video all your problems are mechanical. I have never worked on a Phillips before so I don't know how the mechanical parts work, but here is what I will do. Try to dissemble as mucha as possible of all the controls at the front panel, the switches at the bottom of the vol/div, etc. carefully try to clean, sometimes lubrication is useful, I use wd40. Clean and check that the contacts are touching.The open circuit on that relay can be due to settings of the scope when it was turned off.

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 07:24:23 pm
content: Quote from: dan3460 on December 10, 2016, 07:20:29 pmWhat about the a trace pos not being centered? Adjusting the dc balance pot didnt solve it.Edit: maybe the dc balance trimmer pot resistance is off, maybe it should be replaced. Still, the trace on channel A is deformed no matter what..I did a continuity check on the relay with the scope is on, it conducts no matter the position of the x10 mag switchWhat about adding a touch of solder on the worn conctacts? maybe it could be enough the ensure a good contact..I already cleaned all pots and switches with dry contact cleaner, should i do it again, maybe opening switches and pots?should i use dry or lubrificating products?

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 10, 2016, 08:02:04 pm
content: As far as I can see all these relais are the same type. And should behave the same. From your picture it looks like a coil around a reed relais. From the schematic and I'm not aware a normally closed reed relay exists it should be open if no current running through the coil. If not the reed relais contacts might stuck for whatever reason.By design the reed contacts close if a magnet gets close. It should work even through the coil around the reed contact. So you might try if it closes without power your scope by bringing a small magnet close to it. And as the K1401 is driven from a switch you might check if one side of the coil gets connected to GND if 10x is enabled.As you say the others are closed if you measure them. This sounds odd to me. Sometimes reed relais can stick so slight tapping a closed and un-powered relais might open the contacts (if not fused together).P.S.: I found a different schematic for a Pm3212:https://archive.org/stream/philips_pm3212better readable but the schematics are not identical.

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 08:17:02 pm
content: Quote from: Twoflower on December 10, 2016, 08:02:04 pmFAULTY RELAY CONFIRMED!if i short the... reed contacts together x10 mag is enabled...!...Now what relay should i get...? I've never seen a relay like this.Should i look just for a new reed contact of similar dimensions? Should i desolder the faulty one?Update: i tried with a magnet too, i can hear it switching but nothing happens

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 10, 2016, 08:26:41 pm
content: First you should measure the size of the glass ferule to order a replacement. Search fore reed contact/reed relais at your preferred supplier. They're cheap, probably less than 1€.Can you check if you might be able to get the glass part out or is it glued in? That's the contact part of the relais. If you're lucky you can cut the two wires from the glass part and solder in a new one (careful they break easily).If they're glued in I think the best is to unsolder the whole relais and see how to remove the contact.If it's easy to replace you might think about to replace all reed contacts. Otherwise you should double-check the other ones about reliability.

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 08:35:50 pm
content: Quote from: Twoflower on December 10, 2016, 08:26:41 pmI dont think its glued, there is a bit of slop inside despite being soldered on both ends. Now i'll desolder it and slide it out.PS i love you.

author: Twoflower
author_rank: Frequent Contributor
timestamp: December 10, 2016, 09:01:42 pm
content: If you replace them with the new ones: Handle them very careful as the glass cracks easily (order one or two extra might be a good investment). Probably it's a good idea to solder in two pieces of silver wire into the PCB and solder the reed contact to the wires without bending the contacts of the contact. This will minimize the stress on the device.If you want to solder them directly into the PCB. Please make sure that the wires are bend exactly so they slide into the PCB holes without additional bending that apply a constant stress to the glass.I might be a bit over careful here. But cracking them without noticing it might result in the same problem you have now: A unreliable piece of equipment ;-)

author: Basileus
author_rank: Regular Contributor
timestamp: December 10, 2016, 09:13:28 pm
content: Quote from: Twoflower on December 10, 2016, 09:01:42 pmHehehe.. Dont worry.. I think i'll buy an mg belt of reed contacts..http://www.ebay.it/itm/10-Contatti-Reed-Magnetico-Switch-Ampolla-Induzione14mm-Interruttore-Aperto-/262149741636?hash=item3d09579c44:g:tqEAAOSwkZhWTH5f

author: Basileus
author_rank: Regular Contributor
timestamp: December 11, 2016, 12:04:30 am
content: I gave another good cleaning at the panel controls. I checked with the DMM continuity on the surface of the v/div contacts. It doesnt seem much solid to me. Maybe i should try something stronger to deoxidize those contacts, instead of dry contact cleaner.Trace on channel A is still offset...PS: I also have this "Electric Reactivator" from Svitol, does anybody know if its any good?http://www.svitol.it/en/products/svitol-technik/electric-reactivator/

author: oldway
author_rank: Super Contributor
timestamp: December 11, 2016, 06:21:56 am
content: Do not use anything as contact cleaner, this can make the situation worse.After several years of experience in oscilloscope repair, I only use the KF F2 special contacts.http://fr.farnell.com/kf/1001/lubricant-dry-deoxidising-cl/dp/3916560

author: Basileus
author_rank: Regular Contributor
timestamp: December 11, 2016, 09:18:06 am
content: Quote from: oldway on December 11, 2016, 06:21:56 amWHAT? Damm.I used it twice.I looked for that product and for less than 20-25 euros i cant find it on thet (shipping included)....Second choice?

author: oldway
author_rank: Super Contributor
timestamp: December 11, 2016, 11:29:42 am
content: There are 100ml, 200ml and 500ml cans....100ml cans are cheaper....

author: Basileus
author_rank: Regular Contributor
timestamp: December 11, 2016, 09:19:15 pm
content: Quote from: oldway on December 11, 2016, 11:29:42 amI cant find smaller cans than 500 ml.. Do you think paying 10 euros + 10 of shipping is worth it? Will it work? Who knows..

author: boffin
author_rank: Unknown
timestamp: December 11, 2016, 09:51:12 pm
content: Quote from: Basileus on December 10, 2016, 04:14:19 pmI used 5 Red LEDs, 2k resistor, and didn't bother fiddling the transistor drive. It means it goes from 0-100% in the 1st 3rd of the turn, but I really don't care. Photos here:https://www.eevblog.com/forum/repair/philips-pm-3216-oscilloscope/I have a dodgy Channel A as well, but it appears to be solidly the switch, just waiting for the snow to go away before I drive across town to buy some deoxit.

author: Basileus
author_rank: Regular Contributor
timestamp: December 11, 2016, 10:09:31 pm
content: Quote from: boffin on December 11, 2016, 09:51:12 pmIt took me 10 hours of work but i placed the leds in the sockets on the brackets that hold the crt. Quite sexy i should say!Maybe i should get deoxit, even though a small squeezy tube here in italy is more expensive than gold..Update: a small 2 ml tube of deoxit: 19 euros (ebay). Never mind...Update 2: i think i ll try to use that "electric reactivator" i have from svitol...

author: Basileus
author_rank: Regular Contributor
timestamp: December 12, 2016, 07:41:23 pm
content: I have found this interesting video:https://youtu.be/l-ve0Jk6bGcThis guy cleaned the rotary switches with a damm pencil rubber. I think i'll give it a shot before running to buy 20 euros of "special" products.This guy also said do not spray the u contacts that touch the rotary switch with deoxit because you will damage the scope.. I did it with a generic dry contact cleaner, did i mess something up?

author: cheeseit
author_rank: Regular Contributor
timestamp: December 12, 2016, 08:14:39 pm
content: I've had great success using rubber erasers, followed by a thorough cleaning with compressed air and isopropyl since some (all?) erasers may contain oils. Just make sure that you use the type for pencils and not the coarse kind for ink as kind contains an abrasive that will damage the plating.Some time ago I spent many, many hours dismantling and cleaning every switch on a PM3264, both rotary and push. Philips made great scopes but sure didn't make them easy to service, IMHO. Fun though.

author: Basileus
author_rank: Regular Contributor
timestamp: December 17, 2016, 09:32:41 am
content: Update!The rubber worked, even though i havent cleaned the last rotary contact that is unaccessible without complete disassembly.I havent cleaned the contacts on the mtb because it works perfectly fine.Now i can get a not deformed trace on channel A even though the trace itself its offset beyond trimmer pot range and the amplitude is wrong (1.2v cal 5.2 divs instead of 6 on 0.2 settings).Still, its not stable and i think the problem are the coupling switches, that cause problems on BOTH channels.Unfortunately disassembling the switches and putting them back together is a mess, also because you need to disassemble the whole front panel to reach them.I tried to desolder the line trig control, just to check how they are inside, but i couldnt manage to get the solder out of the through holes.. and the board itself started losing solder mask (no functional problems).Im not very confident in attempting this repair, even though is nearly necessary for me to make the oscilloscope usable. Does anybody got any suggestions on how should i carry this repair?

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 17, 2016, 12:55:21 pm
content: I've got a PM3217 which is the same construction and the zero switch on the B channel is knackered. It's pretty difficult to get to so I've just left it for now. I dread the day something else packs in because I don't want to go through what you're going throughI would stick to a very low wattage iron (15W) or temp controlled one if you have one and use soder-wick and a flux pen. Flux it up, poke the soder-wick on it and drop the iron on top. All the solder will get sucked out in a couple of seconds into the wick. You need to do this to free up anything with more than a few pins. Don't use a solder sucker; they suck the pads off.

author: Basileus
author_rank: Regular Contributor
timestamp: December 17, 2016, 03:32:00 pm
content: Quote from: SingedFingers on December 17, 2016, 12:55:21 pmMmmh i planned carefully what im going to try:If i wanted to desolder the buttons, i would have to remove the rotary switches and assembly to do it. This is out of question, no way.What i think ill try is to dissassemble the front panel switches and buttons, so that i can reach the 3 screws that hold the metal shielding of the coupling controls. Desolder the components over the switches and open the buttons. Probably the contacts are tarnished: i ll get myself one "rubber pecil" to reach them (or if i cant manage to ill try with some 2000 grid sand paper). Reassemble the button without the main spring, insert it from the front and block it with his plastic knob. Do the rest in reverse order.Now i'm really nervous.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: December 17, 2016, 04:00:58 pm
content: A few weeks ago at work, I scrapped a PM series scope (because it's ancient mains filter capacitor smoked and damaged the board beyond economical repair) and subsequently discovered the cause of a similar fault that the same scope had a few years earlier.The channel's input capacitor had broken off on one side hence the lack of input - it was not diagnosed as it would have involved a lot of dismantling which wasn't worth while for a workplace to do on an old kit.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 17, 2016, 04:59:41 pm
content: First thing I do is replace those RIFA smoke grenades. Absolutely deadly things. Haven't been bitten by one yet and intend not being ever.I won't scrap somehing that requires a bit of effort and expenditure. I might learn something.Quote from: Basileus on December 17, 2016, 03:32:00 pmGood luck. I've done worse and succeeded for the sake of getting one useable scope because I had no money.My PM3217 was fortunately just mucky when I got it. It got recapped, a couple of knobs repaired, the X2 cap replaced and recalibrated and that was it.

author: Basileus
author_rank: Regular Contributor
timestamp: December 17, 2016, 06:21:12 pm
content: Quote from: TheWelly888 on December 17, 2016, 04:00:58 pmNo way.The shielding of the coupling controls is SOLDERED ON THE BOARD ITSELF! And the solder joints are under the rotary switches of both channels!Im not confident enough with my soldering skills to deal with that. I cant. Ill spray the switches with contact cleaner and push them a couple of thousands times, hoping the tarnish inside will eventually work loose.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 17, 2016, 06:38:24 pm
content: Ouch. Screw that. I wouldn't even go there.

author: Basileus
author_rank: Regular Contributor
timestamp: December 18, 2016, 12:11:34 pm
content: Quote from: Basileus on December 17, 2016, 06:21:12 pmI cant belive it.It worked! Now the trace doesnt move when wiggling the coupling switches!Still, the trace moves a bit when wiggling the v/div knob, but i'm pretty sure its because i couldnt clean a rotary contact that cant be reached without dismatling. I'll leave it as it is because the trace is fairly stable if left it be.Still, channel A trace is way too much high and cant be correctly centered, amplitude on channel A is wrong and after "cleaning" the coupling switches, both channels display large spikes at the beginning of the higher voltage portion of the square wave (before it didnt and this effect is most notable on 0.2 v/div setting).PS: using a cheap x1 cable bnc to crocodile clips.Here's a immage of it.Should i attempt to calibrate the scope and get rid of that? Unfortunately i don't have a decent waveform generator (just a small kit i built some time ago based on the xr2206 ic) or insulated trimming tools... What could i do?

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 18, 2016, 05:18:35 pm
content: I would probably leave it if I were you. Grab some cheap 10x scope probes before you do anything though and check the the probe compensation with a square wave off your XR2206 based gen. That should indicate any problems with the compensation network and you're good to go.Mine isn't calibrated properly but it's good enough.If you want to cal it you need a relatively complex timebase generator and a voltage reference. Keep an eye out for Heathkit scope calibrators on eBay; they're cheap and good enough for this sort of work.

author: Basileus
author_rank: Regular Contributor
timestamp: December 18, 2016, 06:06:57 pm
content: Quote from: SingedFingers on December 18, 2016, 05:18:35 pmWow! the square wave out my xr2206 is flawless! Cant understand why my cal signal isnt displayed like that.Still, two problems:1-Wrong amplitude on channel A - could i tweak it without messing other stuff?2-Trace on channel A is not correctly centered and when the A pos pot knob is in the middle of the range, the trace sits 4.5 divs about the center. Already tried to tweak it by messing with dc balance trimmer, didnt work. Any ideas?

author: xtoffer
author_rank: Contributor
timestamp: December 18, 2016, 08:08:25 pm
content: Quote from: Basileus on December 18, 2016, 06:06:57 pmHehe contact cleaner sometimes seems like magic. Anyhow so the cal output is also faulty then?About ch A, is the offset independent of v/div setting?Check possible voltage testpoints in the vincinity.If Ch B is working maybe you can compare some components around the dc balance area.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 18, 2016, 08:11:32 pm
content: You should only use the cal output with a 10x probe. Probably why it's wonky.

author: John.S
author_rank: Contributor
timestamp: December 19, 2016, 10:50:08 am
content: Hi,Lots of years ago I owned an Advanced Instruments scope. It too had 1 channel that could not be centered anymore. Since it is long ago I don't remember it exactly anymore, but the problem was a diode ( 1N4148, strangely enough I remember that). At the point the 2 channels were mixed for Alternate/Chop mode they used a couple of small signal diodes. 1 diode suddenly had a higher PN voltage, that lifted the trace so high I could not centre it anymore.I replaced all the diodes around this mixing point, that solved my problem back then.gr. John.

author: tautech
author_rank: Super Contributor
timestamp: December 20, 2016, 07:39:10 am
content: Channel 1 or A is usually the most used and abused of any scope.Consider it may have been abused, probably with an overvoltage event.Knowing that may be the case a study of the schematics should point to areas in the input front end where damage might have occurred.As you have a channel that seems OK why not just trace the signal flow with another scope comparing each test point with the same in the good channel ?

author: Basileus
author_rank: Regular Contributor
timestamp: December 22, 2016, 06:12:05 pm
content: Quote from: John.S on December 19, 2016, 10:50:08 amWow, thats a good suggestion. Unfortunately i measured the forward voltage of the 3 channel A diodes right before the common channel multiv with my dmm and compared them to the 3 on channel B. They seem fine, unfortunately.I dont have another oscilloscope to troubleshoot mine.Yes, the offset on channel A is indipendent from the v/div knob. Already checked every test point on channel A, they are correct and/or similar to channel B. Maybe i should check them again.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 22, 2016, 06:47:42 pm
content: Quote from: Basileus on December 22, 2016, 06:12:05 pmThis is mistake number one. If you're running old scopes, you need one to fix the broken one. Too much time doing that here:

author: Basileus
author_rank: Regular Contributor
timestamp: December 22, 2016, 06:59:18 pm
content: Quote from: SingedFingers on December 22, 2016, 06:47:42 pmActually i have a dso138 kit i got a while ago, but i dont know if its worth mentioning it..Anyway, i noticed that when the channels are coupled to ground, when using the CAL pot the trace moves vertically (channel B not much, 1/8th of division max (up), while channel A goes down by a whole division at least).

author: Basileus
author_rank: Regular Contributor
timestamp: December 24, 2016, 09:05:51 pm
content: Update!Tried to adjust trimmer pot r543 x1 gain channel A, i cant get the right amplitude. Pot is set at minimum and still the 1.2v cal signal is 5.7 div high (0.2 v/div) instead of six. What is going on?

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 24, 2016, 09:17:48 pm
content: I'd check supply voltage to that part of the circuit and check resistors aren't open first. Every DC bias problem I've had with scopes is either a shorted tant pulling the rail down or an open resistor killing bias.Edit: other option is injecting a known good signal into the front end in X-Y mode and tracing it through the amps one after another until you find the Dicky stage. Your DSO 138 can probably handle that actually if you stay away from the CRT plate drivers.

author: boffin
author_rank: Unknown
timestamp: December 30, 2016, 04:22:19 am
content: Quote from: Basileus on December 24, 2016, 09:05:51 pmCheck the trimmer hasn't failed to a higher total resistance. That was the failure on the power supply of my PM3216, a 220R trimmer was 1k5 from end to end.

author: Basileus
author_rank: Regular Contributor
timestamp: December 31, 2016, 03:46:26 pm
content: Quote from: boffin on December 30, 2016, 04:22:19 amAll pots seem good. Checked every resistor for offset values/open. Nothing.I cant figure out where the channel A amps are getting power from. I'll probably try to trubleshoot the whole ps board.Yep, not having another scope to troubleshoot is a problem.Thats why i just got a Tektronix 2215 in "seems in fully working order" for 95 € (shipping from uk to italy included). Pretty good score, would say. I'll stop working until it arrives. If i fix the philips one ill might think about selling it.

author: Greenray
author_rank: Contributor
timestamp: January 01, 2017, 04:25:47 pm
content: Hi.It's been reading your long discussion, that push me to finally open my PM 3212 (more than 20 years old) trying to repair the Cannel B sync.This is the reason that move me to write here instead to open a new discussion.But now I ask you all a right suggestion about it: better to start here or open a new discussion?I thank you so much.-------------------------------Staying on this proper discussion I desire to say to Basileus and SingedFinger some words:Point 1: to have only one old oscilloscope it's not really a mistake.... In any case we can use another oscilloscope to help ourselves to repair the one of we are owner. I hope that you could find some appassionated entusiastic people that occasionally help you with his scope.Point 2: if the spare parts of the REED relays are too expensive or not easy to find, please consider the possibility to buy a broken PM3215, that can be cheeper than a single REED !!!Point 3: if you are not good skilled with your Iron Solder, please consider an alternative to the normal replacement. Only if as I think the contact is normally opened, you can apply the good part over the fault, without remove the coil from the PCB. The route of the signal will remain short as now: the route of the DC that flow int the coil will be a bit more long, but it will be not matter of problems.In any case I suggest to remove the wirings to the glass holder of the contacts. Yes I know, we are not talking about Very High Frequency, but this contact it's better that disappear from the circuit.

author: Basileus
author_rank: Regular Contributor
timestamp: January 02, 2017, 09:17:49 am
content: Quote from: Greenray on January 01, 2017, 04:25:47 pmThere is no need to remove the coil from the pcb. I didnt remove it. The problem is that if you want to solder the new reed contact like the faulty one was soldered before, you need to bend the leads in a half circle and its quite difficult without breaking glass part of the contact.Thats why i'm waiting for a shipment of reed contacts from china i bought a while ago.I think i will scavenge the broken leads from the old reed contact and solder them back in place, so that i only need to trim the leads of the new one, slide it inside the coil and solder it to the old, pre-bent leads.I think its probably better creating a new topic for your problem, to avoid confusion and over-cluttering.

author: Greenray
author_rank: Contributor
timestamp: January 02, 2017, 10:13:40 am
content: Thank you.So I wrote the new discussion:https://www.eevblog.com/forum/index.php?topic=80804.msg1104369#msg1104369

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 03:03:49 pm
content: I'm back on the repair! Now with another scope, i'm checking everything again.-The DC voltages are all fine on channel A;With the scope i noticed that the AC signal Vpp is the same on all pair of transistors and similar to channel A UNTIL PAIR V513 - V514. The signal amplitude on V514 collector is twice the one on V513 collector. Now i'm investigating more in depth on that part of the circuit. I'm really tempted to desolder V514, but i feel like i need to check the components near to it. By testing V514 in circuit with the DMM diode mode, it seems perfectly fine.I might just make a leap of faith, desolder it and check it with a cheap components tester i got. What do you think about it?

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 13, 2017, 03:15:27 pm
content: I'd check resistors around it first.

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 04:04:44 pm
content: Quote from: SingedFingers on January 13, 2017, 03:15:27 pmChecked R559, R558, R567, all good.R558 is quite dodgy because it should be a 17.8k resistor but measures 4.23k ohms. I checked same values resistors across the board and they all give similar readings though.It is connected to what looks like a voltage reference line but its maked "+12E". E? and there are other places were there are other letters, like C. What are those points? i'm quite confused. Cant find anything on google yet.I'm still testing components around that transistor but i cant find anything blatantly wrong.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 13, 2017, 04:13:01 pm
content: Desolder one end of it and test again if you haven't already. Other circuit components may be causing this reading to be offset.

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 04:37:05 pm
content: Quote from: SingedFingers on January 13, 2017, 04:13:01 pmChecked R662 and R658 17.8k ohm resistors that are the normal and inverted counterpart to that resistor. They give nearly the exact same reading, 4.23 ohms. I dont think desoldering it is worth the trouble also because that area of the board is difficult to reach. Its behind the delay line and another cable that is flush with the board runs through that area.Still checking components around.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: January 13, 2017, 05:05:45 pm
content: Ah yeah screw that. Good luck

author: Basileus
author_rank: Regular Contributor
timestamp: January 25, 2017, 10:36:07 am
content: After a break (after getting a Tek 2215 with a faulty DTB and fixing it)I went back to fixing the pm3212. This machine is a damm mistery. I checked every reference voltage across both vertical channels and compared them, nothing. I checked every transistor signal with another scope, nothing. I checked the PSU, seems fine. The fault seems so tiny it cannot be found. The A trace just stays 5-7 div higher than normal with slightly lower amplitude. Tweaking the trimmer pots doesnt do enough. I just cant isolate the fault.Please, does anybody, ANYBODY have a clue on what is going on? I'm so lost.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 25, 2017, 07:02:11 pm
content: The 12E is like the other 12A...12K different 12V supplies with own filter caps (Page 127 right half, center). So you should measure there 12V.Not an expert here, so just thinking loud:I assume you compared both channels within the pre-amp (see attached picture) with no input and the position knob on lower and on mid position. No need to stress the circuit to go too high, just turn the knob on both channels the same way around. What's the values? Are they identical between the channels?Yes->Have you checked also the chopper-multiplexer? There both channels are interleaved and this is the last place were both channels have different circuits.No->Check also the diodes V521/522. Also have a closer look at the source of the wire that just escapes down. The circuit has lots of switches which could be a source of trouble. So Probably compare the voltage there.

author: Basileus
author_rank: Regular Contributor
timestamp: January 25, 2017, 08:56:34 pm
content: Quote from: Twoflower on January 25, 2017, 07:02:11 pmOoohh i see. I checked all the electrolytic caps of the power rails on the main board, readings are within +- 0.20 V of the reference voltages. Both channel power rails are quite similar.I'm checking again both preamps with GND coupling (no input) and both y pos controls at minimum. The voltages on D501 transitors are from 0.10V to 0.20V higher than D601 (channel B). Cant tell if its relevant or they should be spot on. Makes me wonder if its a front end problem.

author: Basileus
author_rank: Regular Contributor
timestamp: January 25, 2017, 09:16:26 pm
content: I'm checking with the DMM (no point in using the scope for DC voltages) and i'm feeling like i'm not going anywhere. I cant tell how much difference between the voltages is suspect. 0.20 V, is it a problem or what?I guess i could make a map with all the readings i get along both channels and post them here. I really cant tell whats wrong.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 25, 2017, 09:19:39 pm
content: I don't expect a missing supply. Somehow there's a offset hidden. Yes this might indicate to a supply problem, but somehow I have the feeling it's not.And if the 200mV matter we'll see.Can you test this again at both the positions I marked in the picture earlier? They come as a pair. So far I can see the signal is amplified differential. If one side fails or the offset between both signal levels is off this could explain what you see. Ideal would be that if the knob is in the middle both marked measurement points has the same voltage. This represents the centre of the screen. A difference will move the trace up/down (regardless if by the pos knob or input signal). The marked spots should contain the signal plus the offset from the position knob.And can you test the voltages with the pos more in the middle? This gives some feeling how much differential voltage per div is expected.And please post the results for also for channel B that we can use this data as master. I assume the change would be the same.

author: Basileus
author_rank: Regular Contributor
timestamp: January 25, 2017, 09:40:12 pm
content: Quote from: Twoflower on January 25, 2017, 09:19:39 pmReadings with:GND coupling, AUTO, composite triggering, ALT V mode, Both channels y pos pot roughly centeredCHANNEL AV522 Anode: 115 mVV521 Anode: 128 mVCHANNEL BV622 Anode: 145 mVV621 Anode: 145 mVWow.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 26, 2017, 05:54:08 pm
content: It seems we're getting somewhere. One point:1. Around this point I'm not sure if the voltages are actually DC if in ALT mode. I haven't fully understood the circuit, but the circuit drawn in between both channels might control which channel is displayed. So if you select ALT you might see only one channel show any voltage while the other is disabled. This change every time the trace is fully drawn. Please use either A (if measure on Channel A) or B.The problem is, that the path through the signal-path is current based. For example the current through R557 is supposed to be 4.2mA and 65µA/div. While the 65µA/div doesn't matter with GND at the input you can ignore that part. I hope your multimeter is doing good at low voltages. Can you measure the following points?1. Setting: POS = middle; Input: GND, select Channel A --> Voltage across R556 and voltage across R5573. Setting: POS = middle; Input: GND, select Channel B --> Voltage across R656 and voltage across R657The voltage calculates like 4.2mA * 301= 1264mV at this point. The POS-Knob offset is not applied to this. This will happen after the V513/514.For the good channel I expect at point 2: 1264mV for both resistors. For the bad one it depends if the problem is left or right side. If the error is already there: about 1382mV. If the error is not present there in it will match the one on channel B.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 01:53:56 pm
content: Quote from: Twoflower on January 26, 2017, 05:54:08 pmHuh...Yes you are right. The circuit in the middle is the channel multivibrator, which controls which channel and how is fed to the last, fixed gain amplifier. In A and B display modes, the voltage at the diodes is DC only, while in ALT and CHOP modes the signal is a square wave (higher frequency for CHOP mode).Actually, my scope doesnt have R557-R556 and C512-C514. There are holes for the components, but looks like they removed them and soldered some wire jumpers. I guess they were removed during an hardware upgrade. (Same thing with channel B).

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 02:01:28 pm
content: Voltages on V514, V513 emitters are 3.45 v and 3.45 v +-0.01 v.On channel B:3.44v3.44vI starting to think that i need a better multimeter.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 02:48:46 pm
content: Hrm. The missing resistors doesn't make the measure of the current easy... We can only hope that measure the potential is sufficient. To get better values from your multimeter you can measure the difference between the upper signal path and the lower. For example measure at the wires at R556 (positive tip of your multimeter) and the wire at R557 (negative tip). As the differential value is supposed to very little the MM will switch to the smallest voltage range and thus you get a good reading.If everything is ideal the measurements would show 0V. Any difference will move the trace up/down. At the R556/557 pair the POS-knob should have no influence, this offset will be applied after the transistors in the signal path.The problem is to identify what's acceptable and what not. The manuals only show currents and not voltages. Probably the best is to attach an external DC voltage to Ch.B (e.g. 1V). And if you measure the difference on the channel B signal path. This will give you a feeling how much voltage at R656-R657 per div is expected.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 07:46:41 pm
content: Quote from: Twoflower on January 27, 2017, 02:48:46 pmOh i feel so dumbcant even use a dmm.I probed here and there and the most suspicious thing i ve found is a difference of 90 mV at the bases of V512- V511.Same transistors on channel B have a difference of 4 mV.Doesnt change by moving the trace or toggling the triggering source control (checked because close to trigger A pickoff). Maybe the "second" stage of the preamplifier is so unbalanced that the last stage (with pos pot) cant rebalance it again. Still, the v difference between the other transistors pair are "reasonable".Probably the fact that channel A is miscalibrated doesnt help too. I fiddled too much with the trimmer pots

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 08:27:03 pm
content: No worries. as long as your DMM and scope didn' did this:that could be fixed.One good rule is to remember the original pot settings before changing them or take a picture (which might help for simple pots, not for 10-turn trimmers). If it's too late: You might be lucky, you have a complete manual of your scope. The bad thing is, depending how many trimmers you touched this can take some time and good understanding of the meaning of the individual knobs.You should try to understand the schematics a bit. Moving the POS doesn't change anything there as the POS poti is located later in the signal path. So Here the poti R543 and 547 might change this. But this looks like only the trigger supposed to be affected. That should have no impact to the traces on the screen. We should save this for later (but you should keep this in mind).Can you please post what you measure at TP4 - TP5 (see picture)? As you see we're down to few mV/div offset. Unfortunately the 7.8mV/div don't say to GND or to the 'other side', so please measure the voltage between TP4 and TP5 as this might be double the value thus easier to measure. Because you wrote earlier that the values on the anodes V521/522 showed some offset (13mV) this might match with the offset you see. You 'only' need to figure out the first place of this mismatch and check what could be the cause there.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 08:43:16 pm
content: Quote from: Twoflower on January 27, 2017, 08:27:03 pmI have found something *interesting*The v difference between tp4 and tp5 (A) is 8.5 mV;The v difference between tp4 and tp5 (B) is 4.4 mV;WHEN SETTING THE CAL POT TO MAX POSITION:The v difference between tp4 and tp5 (A) goes to 18.0 mV, nearly doubling;The v difference between tp4 and tp5 (B) is 3.3 mV;Mmh maybe its caused by the A preamp being miscalibrated..

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 08:57:01 pm
content: That doesn't look good to me. Why does R2 have such a huge influence there on channel A. I would assume something like you see on B or even no visible change at all. Again the signal traces are current based, but that doesn't feel right.Idea: Could it be that one of the V508/509 is blown? Can you check TP4 to GND and TP5 to GND how do they behave if you change the pos? Please do the same on the B TPs. Please post the readings. That helps me to get a better understanding what happens.By the way, the documentation dan3460 posted (3rd post) shows the full calibration process. This can fix the misaligned trimmers. Still it does not note a faulty offset.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 09:09:32 pm
content: Quote from: Twoflower on January 27, 2017, 08:57:01 pmNot R2, R7.I dont have a function generator and other stuff to calibrate it. Still,i have an uncalibrated cheapo fun gen. I could measure the amplitude and frequency with another scope and calibrate the philips one with it.V508 and V509 are socketed and i think i already checked them. Ill check them again.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 09:14:45 pm
content: Quote from: Basileus on January 27, 2017, 09:09:32 pmHuhhhh.. V508 readings are higher than V509.My dmm is a cheapo with the *diode mode* that is also the 2000 range ohms. Cant tell if the values it shows are resistance or voltage drop like a proper diode mode.Still, V509 junctions measure about 850... something and V508 1100. Ill swap their place, lets see if the problem flips.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 09:19:30 pm
content: Ah different poti, OK that explains that you see changes there at all. Completely my fault.Probably it's best to calibrate the scope as good as you can before we continue. This would hopefully reduce the risk that we're chasing some misaligned trimmer. For the amplifiers you can do a lot without a signal source.In 'Diode mode' the DMMs usually show the voltage drop. You can try that: Measure a silicon diode --> about 0.7V.And if you haven't touched the trimmers for chan B you should swap the trannies back after this test.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 09:21:04 pm
content: ITS THE GODDAMM TRANSISTORAlways check things twice. I cant belive i didnt spot it the first time i checked the transistors. Oh well. I made it. Thats all what matters. Looking for replacement now!!

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 09:24:53 pm
content: Sure that's the trannie or could it be oxidized leads causing bad contacts in the socket?But at least it is narrowed down to a simple clean or replacement. It looks like your scope gets better by the date!

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 09:42:42 pm
content: Quote from: Twoflower on January 27, 2017, 09:24:53 pmI tried to clean the leads with contact cleaner and scrape them with a knife. Didnt do anything. Trace is still offset, if i swap the transistors the problem flips. I cant recognize the faulty transistor anymore, the readings seem quite similar now.. I guess ill get two new BF450 or similar. Meanwhile, ill try to clean these i have with some fine sand paper. Thank you Twoflower, im so high right now ^_^.Yes the scope is slowing getting better. I replaced the reed contact, but seems like the switch doesnt work anymore. Same stuff as the other one. Ill have to open it, glue it, spend 2 hours straight trying to fit the springs again. At least i know what to do, right?Then some cal, and we are good.

author: Twoflower
author_rank: Frequent Contributor
timestamp: January 27, 2017, 09:51:07 pm
content: OK, the oxidized leads was just a last straw. It seems that you need to get hands on some replacement BF450.Crossing my fingers that you don't need so long to get the switch back together.

author: Basileus
author_rank: Regular Contributor
timestamp: January 27, 2017, 10:09:08 pm
content: Quote from: Twoflower on January 27, 2017, 09:51:07 pmHuuhhhhhhhh....Sand paper didnt do the trick but...Moving it to V511 did. Now it works fine. Still, i should probably get a replacementNow the trace is PERFECTLY CENTERED, but i wonder if that transistor placed in V511 will mess up the triggering.