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Do you have the original oscillator available to swap in and rule that out as an issue? Pictures of the top & bottom of board might also be helpful for identifying any mistakes.

Sure, that would work fine too; it would be the same electrically.

Yeah, if you've got continuity between all those points, I wouldn't be surprised if the sound chip is the problem. Just wanted to make sure it wasn't something else first, since the sound chip is a custom Apple ASIC and it might be difficult to find a replacement for it.

My thoughts on this: You're right, the leakage on that board is pretty horrible. I wouldn't write off repairing it as impossible per se, but it certainly won't be easy. IMO, given how rare and expensive working IIfx boards tend to be, it wouldn't hurt to at least try fixing it. It doesn't look...

Glad to hear you got your board back. I'm not sure if there's a way to test the sound chip in software (hopefully somebody else can chime in on this), but here's part of the schematic relevant to the sound circuitry for the LC III: Pin 10 of the chip labelled 'U1' is the sound output for the...

Capacitors have reference designators starting with C, and crystals have reference designators starting with Y.

I don't see any more corroded traces, but I do see some crusty vias. Is there continuity between Pin 2 of UG5 and Pin 15 of the EGRET? What about between Pin 20 of UF8 and Pin 4 of the PSU connector?

It's certainly possible that one of the missing caps rolling around on the board and shorting things out could've damaged it, but leaked electrolyte typically won't cause permanent electrical damage aside from corrosion, etc. I'm not sure if the caps not being in circuit would cause damage, though.

Here's another corroded trace:

Scraping the solder mask off the trace near the ROM will work. I'd put a battery in when testing just to be safe (take it out of course when working on the board though).

Yeah, that trace near Y1 is definitely bad. Also, are you trying to turn it on with or without the PRAM battery?

Sorry about that, my mistake. Yes, the 34064 is needed for reset. That's good, the reset circuit is fine then. I do spot at least one corroded trace in your last photo, though, so there may be some others that could be causing problems. If you can take some more pictures of the top and bottom...

The 8-pin IC needed for reset should be labeled "36064" (the EGRET it sits next to is needed for reset too). Reflowing the pins may help, at least it got an LC II I used to have from showing no signs of life to getting to the blinking "?" screen (albeit without sound). Before reflowing the pins...

Given that the stock caps had leaked to the point where they fell off the board, I'd definitely wash it to make sure any residual electrolyte is cleaned off. The fact that you're getting static from the speaker is also a sign of remaining electrolyte left on the board. There are 4 little SOIC-8...

Your repair work on that IIci looks really clean! I'm dealing with a similar issue on my newly acquired LC II, a whole bunch of capacitor crap got under the chips for the sound circuit and ate through a bunch of traces.  :-/

Do you have a picture(s) of the corrosion? The way you describe it makes it sound like a lost cause, especially if the solder mask (green layer) is peeling away.

According to the post I linked, the 16-pin resistor networks will work if offset by 1 position (in other words you'll have 2 unused holes on one side of the network and 2 unused holes on the other side). The datasheet for the stock filters show that the two pins on each end (1, 10, 11, 20) are...

Update: I got around to working on this machine again. The epoxy I linked to above does work for the standoffs, but not the cracks in the back panel. I'm assuming this is because there's so little surface area to bond inside the crack in the back panel, and I'm going to look into other methods...

Nice to hear you got the keyboard working  :D

@SalvationCoder The way you describe your LC acting makes it sound more like a power supply issue than a motherboard one. Definitely try recapping one of the power supplies first; it'll be real difficult to determine if something other than the caps is wrong with the power supply unless you do...