Burnt Müller welding machine PCB (anyone with a simular pcb?)

[printplaatreparatie.nl]

Hi there, first a brief introduction as I'm new to the forum. My name is Peter, and I have a small PCB repairshop, inspired by Daves video's among others. I rarely visit forums, but am planning to spend some more time here, and maybe help others as well!

I'm facing a problem with reverse engineering a burnt pcb, and thought you guys might have information.

A client asked me to repair a print from his 1995 Müller welding machine. The .68uF paper cap was blown, and some components burnt for a while, as is visible in the pictures. I'll include some close-ups in the next post. Most components are still fine but I have trouble identifying a burnt resistor (can't even measure small portions, but maybe after some more cleaning) and the three two-legged components (filters?) next to it, aswel as the originally yellow and blue film capacitors.

Help would be greatly appriciated in the form of pictures of an not-so-burned pcb, or educated guesses about the components. The name of the pcb is Feldreglung FR-01, and it had the number 291299 printed in the copper layer, which might as well be a datecode.

Thanks in advance!

[EDIT: changed topic name]

[printplaatreparatie.nl]

Find some close-ups attached.

[printplaatreparatie.nl]

Overview pics.

[Yansi]

How did that happen?  Look like there may have been some tantalum fire starter action there, which continued to a bigger fire due to some kind of oil residue on the board. What is that brown/black schmoo on the pcb? That does not look like a clean electrical fire.

[printplaatreparatie.nl]

It's indeed possible that the tantalum started the fire, but to me it looks like the paper cap sprayed its oil around. To support this claim: right at the center of the big resistor there is a clean-ish space right behind the insulated leg of the smaller 1% resistor in front of it.

[Yansi]

There is absolutely no oil in the small cap on the PCB. That is a metalized paper, dry as a dead dingo donger. (when cracked, they allow moisture in and then they can blow up if enough power applied, but still would not produce the oily mess).

The other red foil caps are MKT or MKP (polyester or polypropylene dielectric)

Or what oil cap do you refer to?

[MadTux]

Feldregelung FR-01 means something lile (magnetic) field regulation in German, something that is rather used in big DC motors (rotation speed) and generators (constant output voltage).

So I would expect that this is not a normal arc welder but rather something like a generator with build in welding machine where the generator part has failed and you've got the burnt out output regulator module.
https://autoline.de/-/Verkauf/Schweissgerate/Mueller-Opladen-MULLER-OPLADEN-GDS-252--18071617105753128300

Since this thing doesn't look like to be easily fixable, it might be worth to get the rest of the machine and see wether a replacement can be hacked together, depending on the replacement cost of that thing. The circuitry isn't too complex, so I'd rather start a redesign instead of reverse engineering everything.

[Yansi]

AAAaaaaw! Now that makes sense. It is a "genset welder". And the crud is probably a good ol' mix of engine oil and dust, awful crap.

I think it could be fixed (seen much worse PCBs fixed here on the blog), but at least one would need to reverse engineer it thoroughly, or get a spare board to copy from.

[printplaatreparatie.nl]

I'm referring to the .69uF paper capwhich has come off the pcb. I thought they contained a bit of oil as well, but I might be wrong. The oil-dust combination (called smout by technicians here) might indeed be from the generator. I didn't know it would be this type of a welding machine, good thinking! I'll ask the client about it.

[Yansi]

On the cap you can clearly see letter MP: Metallized Paper.

There is absolutely no oil in these.  There may just be only a bit of moisture ingress, as these WIMA transparent caps are very well known pieces of shit, that crack, moisture gets then in and then they blow up awesomely due to the leakage current and heating, if enough power applied to them.

That one on the photo does not even seem cracked, very unlikely it was a cause of that carnage. 

Sure, there are paper in oil caps, but those are metal cans of quite larger size. Never seen a plastic oil containing cap, that could be soldered to pcb like this.

Paper oil caps are mostly used just as a power factor compensation or motor run caps. Not much use of them beyond that.  (maybe some high voltage filter caps too)

[printplaatreparatie.nl]

Actually I stil suspect the paper cap, but thanks for learning me that there is no oil inside. I repaired quite some pcb's with blown WIMA paper caps, but now I learned that the crap they spew out was from moisture. I added two more pictures with different angles. As you can see it cracked badly, but of course it can be due to the heat generated by the tantalum-oil-diesel-dust fireworks.

Anyway, I still hope somebody has a picture of a working board to share, it would save quitte some thinking. Client told me it's indeed a welding machine that takes diesel, so the expectation of MadTux was correct. As I have quite a lot of other projects to do right now, I'll leave this project on the shelve for a month or so, in the hope that this topic will result in a nice and crisp picture for me I'll share the results!

[EDIT: Typo]

[Yansi]

Okay then, this side of the cap look very well blown!

But sure, no oil in it, and the fire may have spread due to the crud on the PCB and the tantalum firestarters may have added to it.