A3640 short to ground

[Mr. Toast]

Intro: Yes, I'm new and this is my first post. Revisiting my Amiga roots. I am attempting to rehab a second A3640. Have one working. Both rev 3.1. Caps replaced on the working one. Caps removed from the troubled one. Pads clean and serviceable.

Need some help from you folks:

Even with all the caps carefully pulled, I am reading 19.1 ohms across the + and - rails indicating a short-to-ground. I found a damaged non-polarized 220pF at C102F which was cleaned and swapped from the working unit for testing.

Thoroughly inspected traces to insure integrity-no apparent issues (at 15x optical).

Sadly, my A4000 mobo is out for repair so I have no test system at the moment. I don't have any fancy test equipment but I do have reasonably decent SMT soldering and trace repair skills.

Any ideas what might cause a short-to-ground of 19.1 ohms across this + and - power rail?

[xArtx]

You can find it with a multimeter.
Set it to lowest range resistance, and hunt till you find a short of the lowest possible reading.

I’d check across ceramic capacitors because they can crack, and also across RAM and other chip supply pins.

[Mr. Toast]

Update: Caps, res and fuse components check out good. Have removed all common passives and still reading a short to ground. Acill proposes that I probably have a PCB compromised by a leaked cap. I might have to look to Chucky Hertell's for a new PCB.

Following Alice down the rabbit hole :/

[bebek]

Have you removed cpu?it has low resistance.

[Mr. Toast]

Originally Posted by bebek

Have you removed cpu?it has low resistance.

Yes. And still no such luck. More and more it is looking like the PCB is compromised. I expected to see something cosmetic but nothing to indicate corrosion. I've also taken a fair bit of ESD precautions during disassembly and removal, as well as all the bench work.

I appreciate the ideas. Welcoming others.