PART 2 Industrial PCB Repair Without Schematics - Practical Example - MIG Welder

[@delboy_1]

Great job, fitted the board and the welder is back in working order. The bonus was following the trouble shooting process. Much appreciated.

[@Dunbar0740]

This has become my favorite who-done-it channel.

[@lonndawg7554]

I think overall this was an awesome exercise in techniques for repairing things, we had a somewhat unusual condition to examine, and we found a lot of clues like a resistor that was running hot, and I absolutely am glad you explained everything and got out the calculations, those were important to explore to explain to us this was an excellent opportunity to do that because it is important to understand current draws and some of the dynamics that can be involved with the circuit and you gave us lots of thoughts and examples as to why something would draw excessive current also exploring the op amp that was fantastic, and how after removal you showed us some methods of investigation to see if the part was operational. Again overall the depth of this repair was very informative. To me this video is a keeper because of some of the things that were explored and discussed. Great job I just had to make a comment 🙂

[@LearnElectronicsRepair]

And thank you for your comment. It made me blush somewhat, but yeah this is a good video.

[@glennkingdon5129]

Great two part repair, really enjoy watching you figure out how a circuit works and look for problems in that circuit.

[@sparkmanuk]

Really hope you do more industrial repair videos, as you have said that’s where the money is in repair.

[@LearnElectronicsRepair]

Me too - I get less of this sort of work than I would like. Mainly computer and audio repairs at the moment

[@michaelbrown2470]

Looks like my guess from the previous video was correct. Yeah for me! I had the exact problem with a Buttkicker amp in the protection circuit. That case was two 12 volt zeners in series. I figure when one failed the increased current in the zener-zener-resistor path burned out the second zener (both failed short). Then the resistor heated up so much I couldn't decode the color bands. It was measured at 1K. The schematic showed 1.2K. I replaced all three components using a 1.2K-ohm, 5-Watt instead of the 2-Watt, resistor and, as suggested by another commenter, I kept the components raised above the board for better cooling.

[@LearnElectronicsRepair]

Yeah well done on this one. Figuring it was a Zener was smart but then figuring it must he hidden, so probably under those resistors, was really good. No doubt you are, or will be, a very good repair tech 👍

[@foogadgets]

As usual a video packet with your impressive experience of troubleshooting electronics. Very interesting and entertaining to see. Thanks Richard!

[@CTCTraining1]

Excellent work. Love to follow the thought process as you worked your way around the board 😀👍

[@bikefarmtaiwan1800]

Great video - love the industrial stuff !

[@heleneivers7669]

strange that last week my WEM copycat had the same problem with an 18 v zener. but was easy to find. love your videos. thanks Richard.

[@markhaynes205]

Loved this episode rich

[@harveystedham9490]

Did the welder work when this PCB returned to Ireland? As for basic MIG welder operation. The MIG torch has a trigger, once pressed this will open the circuit, turn on the gas solenoid (preferably a split second or so before) firing up the wire feed motor (I think these are normally 24V DC). MIG welding is typically adjusted on a rotary dial (modern inverter ones at least) with a voltage range of circa 13V-30V (smaller machines will top out around 24-25V) and then another dial will adjust the wire feed speed/amps (directly related). Amps will typically be, maybe as low as 50 at the minimum, never really looked, up to 300-350amps. Maybe more for a monster machine. Most smaller single phase machines top out at 150-180 amps on a 10A supply, 180-200 amps on a 15A supply. We have a couple of 250A machines at work on 15A supplies but they are never high, typically need a 25A+ supply to run flat out.

[@budgetmerch]

Enjoyed watching this - love fault-finding. Nice job. Pesky Zener diode, completely hidden from view. 🤣🤣

[@robinedminson6461]

Nice job - I do really enjoy your videos. Keep it up :)

[@orion4219]

Great job as usual Richard. Any chance of posting the make and model of welder for the benefit of others?

[@GregM]

Nice fix on a cramped PCB with all those hidden compnents :)

[@fouazhdib6813]

very useful , thank you master

[@Mcfreddo]

Yes, I learned.

[@Lightrunner.]

Good work Richard🤗👍👍👍 A tip, take a little bit flux at the ic pins . The work with the desoldering gun would be easyer.

[@LearnElectronicsRepair]

I find that flux actually blocks up my vacuum desoldering tool, maybe it is due to the type of flux I am using?

[@Lightrunner.]

@LearnElectronicsRepair i do... i take a little bit of flux (tiny point at every pin ) Set my desoldering gun at 350° C. Then stir around the solder joint 1-2 seconds and pull the trigger. With leaded solder no problem. With unleaded solder you must stir longer and every second or third soldering point clean the desoldering gun with the hand drill or similar that was included. If you done, hold the trigger and the rest of flux will evaporates in the desoldering gun.

[@LearnElectronicsRepair]

@@Lightrunner. Do you find you need to use hot air plus the desoldering gun at the same time when for example recapping a motherboard?

[@Lightrunner.]

@@LearnElectronicsRepair no i wouldn't . I pull out the two pin through hole caps. I use my hot air or tweezer at smd ceramic caps. Desolder through hole components exposed with hot air usually result in damage to the circuit board. Because, have you three pin caps at the primary side (230V~, 325V-), yes i would use it eventuelly if my desolder gun or desolder braid doesn't work. If anything doesn't work, my Dremel with 0.5mm drill catch them all😳😏.

[@Dutch_off_grid_homesteading]

Heya, that is nice some hidden components you couldn't see easely so you were write the 1st time with messering all the idiots

[@henkw1562]

I have 2 questions: was the zener getting hot? If you could not have read the value on the zener how do proceed to extract the right voltage of it? We had to wait a day but it was worth it. Well done. Best regards Henk

[@LearnElectronicsRepair]

The Zener would not get hot as I proved in the first video that whatever was drawing current from the 820R resistor could only dissipate 0.08W max.

[@Sam-lk6eo]

Why do they lean the small capacitors over and not stand them up straight ? I notice that on a welder circuit board that was not working right ! Is there any special reason please !

[@TheUnofficialMaker]

was the chip bad or just the zener?

[@greengrayradio1394]

I looked at tke logo on the new 324.. Resembles the TI logo, but not quite like it. Chinesium?

[@anthonydenn4345]

Nice job Richard. The through holes on that board aren't the best alright. Funny how the bad part is hidden away under the resistor. Almost like they designed it that way 😄

[@budgetmerch]

It's a 5 watt resistor, too, so it's placement could easily have contributed to the failure of the Zener if that was getting hot - like putting it inside an oven... 😕

[@LearnElectronicsRepair]

@@budgetmerch It's also intereting because those two 5W resistors do not fit the footprint of the PCB. Do you think the manufacturer found they needed to upgrade the wattage of these resistors after making the PCB, or maybe somebody replaced them with the wrong type (higher wattage) on a previous repair because that is what they had?

[@anthonydenn4345]

@@LearnElectronicsRepair Maybe they used a board from a previous welder model that had a lower output power. Dunno, but it's interesting none the less.

[@Manticore1960]

I recently repaired a computer monitor PSU. The controller chip had failed S/C damaging 2 zeners. Both failed with a low resistance. One read 7Ω & the other 99Ω. I don't know if zeners are actually designed to fail that way to protect the components they are supplying, or whether it's just coincidence. 🤷‍♂

[@Manticore1960]

Makes sense that the resistor was used to supply a zener for the Vcc, rather than being used as a simple voltage dropper. Didn't help that it was hidden under another component. 🙄

[@vinnieluther6589]

It would have been interesting to hook up a test rig to see if the wire feed motor was actuated and at what duty cycle when triggered before and after. Also if the gas valve was triggered and how long the delay was.

[@LearnElectronicsRepair]

The owner goes back to the UK tomorrow so I needed to get it back to him. He will surely let us know if it now works correctly

[@BkR090]

40:57 heat most likely burned the zener.

[@DrFiero]

And it might now repeat-fail sooner since the leg of the 5W resistor is shorter, putting it even closer to the new zener! Snip both legs and extend it up maybe for more air gap cooling?

[@LearnElectronicsRepair]

@@DrFiero That is a fair point and there is plenty of space in there. Rodger if you are reading, can you give us an update and check the temperature of the 0.15R resistor when you refit the PCB to the welder?

[@stephenbeswick2163]

I have been trying to find your sort curuict usb tester on PVC way can you please steve b

[@robtitheridge9708]

Nice bit of fault finding wouls of taken 10 minuets if you had the circuit to hand. but half the fun is the reverse engeneering ,but thats getting harder with multi layer boards.

[@LearnElectronicsRepair]

And that is also why there is good money in this sort of PCB repair as most people won't touch them

[@greengrayradio1394]

You found the problematic parallel "leaker" there! I find that cutting the pins right at the IC package with the straight edge of the cutters close to the package does the cleanest job. We were taught this when I worked in the industry. ICs were plentiful, the PCBs not..

[@LearnElectronicsRepair]

I agree. It just so happened I also wanted to test the LM324 out of circuit for the purposes of this video which meant I had to cut the legs lower down. This in turn made it much harder to remove the remaining pins from the PCB. I did a fair bit of cursing off camera LOL but I think I got away with it by some clever editing 😂

[@kgsalvage6306]

That sneaky zener. Hidden under the resistor. I hate cheap PCBs. You end up making repairs other than the issue.

[@LearnElectronicsRepair]

Yeah the pesky little thing! Made for a great video though 😉