LC II Reverse polarity capacitor

[Challenger 1983]

I accidentally soldered a tantalum capacitor in backwards on C21, I was try to diagnose a faulty power supply and I decided to resolder all the caps on the logic board to check that they weren’t the problem, the power supply was dying but I’m still worried i fried the board, am i okay?

 

[IlikeTech]

Did you power it up with the cap backwards?  if not just turn it around.

 

[Challenger 1983]

I powered it up with the cap backwards yes

 

[Challenger 1983]

Is there any chance that it’s only the capacitor that is damaged and the board is fine?

 

[erichelgeson]

any chance

Yes, there is a chance. I saw someone replace a tantalum cap backwards a few times and blow it each time - did work after they realized it was backwards.

 

[Challenger 1983]

Yes, there is a chance. I saw someone replace a tantalum cap backwards a few times and blow it each time - did work after they realized it was backwards.

The capacitor itself looks fine and there’s no direct shorts to ground anywhere, I’ll switch it around and see if everything is okay, I still need to get a new power supply, but does anyone know what C21 does? 

 

[mmx01]

C21 is a cap on 8V power rail which is powering audio related stuff. Check PIN14 of UB10/DFAC chip. Reverse polarised caps explode as they become shorts for reverse voltage. UB10 could have been shorted, if PIN14 stays low = 0V after the cap has been correctly installed you are ouf of luck.

Check also UA9 which is 12V-8V volage regulator, you should have 8V on PIN8, since it is powered by 12V main rail short of UA9 could shutdown power supply i.e. overcurrent protection.

 

[Challenger 1983]

Thanks for the Info, It appeared the problem with the board was a bunch of CPU traces that rotted themselves out from Cap goo