Logic board failure - what to replace?

[djpumpkin]

I have a performa 520 Logic Board that was working quite happily in a Color Classic. After not being used for a month the machine suddenly won't start up. It works fine with the original CC board.

Would a bad capacitor on the LG completely prevent a CC from powering up? I've replaced a couple of them - but so far nothing. I also replaced the PRAM battery. Is there any other component that could have suddenly failed?

It's strange as there were no symptoms of impeding doom prior to the board failure.

 

[trag]

I am not familiar with the circuitry on the 520. However, there are Mac logic boards (IIci, e.g.) which will not activate the power supply if certain capacitors have failed.

Also, leaked goo from the capacitors can be extremely difficult to see and may cause shorts (mildly conductive goo) or opens (corrosive goo eats away traces, solder, pins and vias) on the logic board.

The first thing I would try is to give the logic board a good washing (several methods recommended in threads at these fora). If that doesn't work, then try replacing the remaining capacitors.

If that doesn't work, decide whether you want to try to trouble shoot it to a lower level.

 

[djpumpkin]

Thanks for your reply.

I'll try to wash the board and maybe recap if that fails. Beyond this I wouldn't know what else to look at - and wouldn't really want to spend much more time on it.

 

[LC_575]

The 520 boards, if anything like the 575 boards, are not very complex (at least not as much as that of a IIci). Caps are the only SMT items that would cause a problem but I doubt one would have radically failed in as little time as a month.

Check the loom/board connector. Make sure 520 board really is all the way in.

Take a look at the ADB connector(s) too. It's a stretch but the connector might just be too loose to adequately contact the keyb pins.