VOGONS


First post, by Deksor

User metadata
Rank l33t
Rank
l33t

Hello everyone, I bought this Schneider EuroPC which in the current state doesn't POST.

After opening it up, I noticed that there was a battery and that it leaked.

Here are shots of the motherboard
ekRbNeQl.jpg
SBDCcOPl.jpg

I tried my best to clean that mess but the computer still doesn't POST.

After hooking up a POST card, I noticed that the reset line was constantly on, but there's still some activity in there as I saw a code "04" and "24" popping up. But they only pop sometimes, which is weird.

Another thing to note is that the traces look in a rather good shape considering the leakage that have been happening there. Most of the components' legs are green and vias are green too, but that's it.

As simple as this computer looks, I'm not sure where to check, because the area of leakage is so massive and the traces look good enough.

Reply 1 of 17, by derSammler

User metadata
Rank l33t
Rank
l33t
Deksor wrote on 2020-05-22, 15:36:

Another thing to note is that the traces look in a rather good shape considering the leakage that have been happening there. Most of the components' legs are green and vias are green too, but that's it.

No, they don't. They look pretty bad actually. I can easily spot at least half a dozen broken traces, the corroded vias are most likely all dead, and the surface-mounted chips like JIM and PVC4 need reflowing. Be prepared to spend days or even weeks fixing this.

http://retro-net.de/blog.html

Reply 3 of 17, by computerguy08

User metadata
Rank Member
Rank
Member

What kind of POST card do you have ?

AFAIK, most XT systems do not output debug codes on port 80h, which is used by the majority of POST cards.

Your best friend here would be Ruud's diagnostic ROM and a LPT debug card.

Reply 4 of 17, by derSammler

User metadata
Rank l33t
Rank
l33t
Deksor wrote on 2020-05-22, 15:57:

Which traces did you spot ?

pcb.jpg
Filename
pcb.jpg
File size
136.67 KiB
Views
213 views
File license
Fair use/fair dealing exception

Just a few. There are at least twice as many in that small portion. The damage is really severe. All the vias must be redone as well.

Note that you need to sand down the protective layer to see the real damage. Doing continuity tests isn't enough, as you have high-frequenzy signals running thru the traces. A damaged trace may still have continuity, but f*cks up the actual signals.

Last edited by derSammler on 2020-05-22, 16:11. Edited 2 times in total.

http://retro-net.de/blog.html

Reply 6 of 17, by computerguy08

User metadata
Rank Member
Rank
Member
Deksor wrote on 2020-05-22, 16:10:

A regular one. I know it shouldn't, but this one does in fact display something.

I had this happen on my dead XT board as well (random codes from time to time). It turns out they are misreporting. The ISA POST cards are mainly designed to work with 286 and above.

Last edited by computerguy08 on 2020-05-22, 16:14. Edited 1 time in total.

Reply 8 of 17, by konc

User metadata
Rank Oldbie
Rank
Oldbie
derSammler wrote on 2020-05-22, 15:42:

No, they don't. They look pretty bad actually.

Exactly this. Sorry, I don't want to spoil the fun but just in case it saves the trouble, this is (another) one very damaged EuroPC. I'd bet it's not fixable, I've seen many in better condition that even after extensive work on them never returned to life.

Reply 9 of 17, by Miphee

User metadata
Rank Member
Rank
Member

The traces are all there so it's not that serious.
Clean it up, apply solder to the joints, check continuity, rewire broken traces. It takes time but it's doable.

Reply 10 of 17, by derSammler

User metadata
Rank l33t
Rank
l33t

You need to do it right, otherwise it will stop working again (and maybe for good) not long after. You need to sand down every area with leakage and desolder all components there. There are vias and traces under those chips and the leaked alkaline solution from the battery will continue eating the copper. A quick fix just to get it running again is not what you want to do - or should do.

It certainly is doable, I fixed similarly damaged boards in the past. But it's a lot of work and rushing is out of place. I would start giving it a bath in a 50% vinegar solution for some hours and then cleaning it using WD40. After that, you'll see all the damage more clearly.

http://retro-net.de/blog.html

Reply 11 of 17, by Miphee

User metadata
Rank Member
Rank
Member

Waaay too much work. Even DIP chips offer enough protection from corrosion so taking them off is pointless. SMDs are even tighter on the board.
Sanding on tiny traces? No. Expose as little of them as possible to avoid further damage. If you find a continuity error, fix it with wire on the other side.
A clean and rewired board won't fail miraculously on it's own.

Reply 13 of 17, by konc

User metadata
Rank Oldbie
Rank
Oldbie
Miphee wrote on 2020-05-22, 20:08:

Waaay too much work. Even DIP chips offer enough protection from corrosion so taking them off is pointless. SMDs are even tighter on the board.
Sanding on tiny traces? No. Expose as little of them as possible to avoid further damage. If you find a continuity error, fix it with wire on the other side.
A clean and rewired board won't fail miraculously on it's own.

Yeah OK you clearly haven't seen the magic below a EuroPC's components which looks "fairly good". Spoiler: this one doesn't even look like that.
Don't get me wrong, I'm not saying it's not fixable. Everything is if you're skilled enough and the board is not multi-layered. I'm just saying that this one requires excessive work, it's not your typical 286/386 that has some damage around the keyb connector.

Reply 14 of 17, by Miphee

User metadata
Rank Member
Rank
Member
konc wrote on 2020-05-22, 22:53:

it's not your typical 286/386 that has some damage around the keyb connector.

A chip is a chip in every computer, the layout doesn't matter. I actually removed QFP, PLC and smaller DIP packaged chips from heavily corroded boards and the gunk simply won't get under the chip (~0,4 mm for QFP). The only exceptions are large DIP chips but even then the corrosion is minimal especially if it's socketed. The leaking substance is thick and won't flow under tight spaces, simple physics. This Schneider board is in excellent shape compared to those.
On the other hand removing these proprietary chips without damage is difficult and putting them back is next to impossible if the pads are already damaged. A simple clean&reflow is more than enough. It's pointless to create problems where none exist.

Reply 15 of 17, by derSammler

User metadata
Rank l33t
Rank
l33t

@Miphee: you certainly have no idea how to fix such damages apart from the quick&dirty way. The leaked alkaline solution under the chips won't just magically disappear because you ignore it being there. The corrosion will go on instead and cause more damaga over time.

Also, have a look at that video:
https://www.youtube.com/watch?v=kNhVQWH318M

http://retro-net.de/blog.html

Reply 16 of 17, by Miphee

User metadata
Rank Member
Rank
Member
derSammler wrote on 2020-05-23, 07:06:

@Miphee: you certainly have no idea how to fix such damages apart from the quick&dirty way.

I have repaired hundreds of boards successfully so I know what I'm talking about. Anybody suggesting SANDING tiny traces has no place anywhere near electronics.

Reply 17 of 17, by Deksor

User metadata
Rank l33t
Rank
l33t

Well I've watched that video.

The reason I said traces looked rather good was because for the most part they look intact. Some don't as you pointed out, but in comparison to what I've seen on some computers, it looks miles better. I'll watch what to do there. I don't think I'll use sandpaper, I'll try to find something more precise (maybe fiber glass ?) to scratch the traces only.

As for the chips, I'm rather skeptical at reflowing the smds. Not that I don't want to do this, but my hot air desoldering skills are terrible, and the corrosion won't help either here ...
As for the TTL chips, I may end up swapping them, they should be easier to remove than the SMDs (though I've tried and it's pretty hard too, thanks to the corrosion ...)