Exploding tantalums are easily repairable. If you can find what values it had replace it. Had an ISA Tseng ET4000AX that blew a tantalum cap last week and it is running again with a new cap on it.
It might have been the source of the problem but to be sure I would first do some continuity tests to see if power goes where it has to go. 😀

SarahWalker wrote:

Hi peoples! […]
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Hi peoples!

I was playing around with some old, seemingly broken, motherboards, seeing if I could coax them back into life. After fixing a 386DX/20 board, I had a look at an old 286/10 I had lying around. It wouldn't power on at all, making me suspect a short somewhere. As I was examining the board, I foolishly tried to power it on again, at which point one of the capacitors exploded. For your amusement I attach a photo of this :

bang.JPG

Now, my questions are :
1) Is the motherboard likely to be repairable after this?
2) Is the now exploded capacitor likely to have been the source of the short, or a side-effect of something else broken on the board?
3) Will I ever be brave enough to apply power to this board ever again?

As member Nvm1 already hinted the short was probably in the exploding tantalum capacitor.

Shorts in old tantalum caps is not very uncommon, I had a video card with a shorted tantalum last year. The system refused to power on with the video card installed eventhough I used an AT PSU... I bet the cap would have exploded if I kept trying.

Firstly welcome to the forums... I have not seen your username until now.

Secondly, it's great to see someone else tinker with 286/386 motherboards... I have been feeling quite outnumbered for a while now with PCI/AGP people so it's good to have the company!

To your question, yes... these little critters pop from time to time and are easily enough replaced. It may be worthwhile changing them all out to give the board a bit of a service. Board should be ok afterward.

Thanks for posting!

Just take a look at the markings on nearby similar looking caps (there's at least 5 other orange ones).

It's always possible other tantalums explode as well, but just keep changing them. Another matter is whether you want to replace these with new tantalums or perhaps with something else, like ceramic or electrolytic capacitors.

386_junkie wrote:

Firstly welcome to the forums... I have not seen your username until now.

I believe that SarahWalker is also very much involved with PCem.

386_junkie wrote:

Secondly, it's great to see someone else tinker with 286/386 motherboards... I have been feeling quite outnumbered for a while now with PCI/AGP people so it's good to have the company!

I also recently acquired a 286 and love to play around with these old systems - refer this post for a pic of the PC: Possible problem with an old AT Power Supply Unit?

what is going on to the right of the C22 label? is that a problem in the board, or a piece of the blown cap sitting on top of the board, or what?

You can replace that with a regular (or even a polymer) electrolytic capacitor. Tantalums aren't used much anymore.

Looks almost like flux.

Edit:
But it probably just a pice of the blown and a small burn mark.

I didn't actually notice that before taking the photo, but yes, it looks like part of the capacitor hit the board and caused a slight burn. It doesn't look like it went deep enough to cause any actual damage, but I'll do some continuity checking on it.

Update - I spent a couple of hours recapping the board, and it now actually works!

Genuinely thrilled about this, I'd assumed it was dead forever.

Curiously, 3Dbench is only 0.4 FPS slower on this 286/10 than it was on the 386DX/20 (actually running at 16) that I'd repaired prior to this.

Had a mosfet pop on my msi 6182 last night, made me sad 🙁
Was interesting how the system kept on running till I killed the power, the mosfet acted like a spark gap 😮