I've recently acquired a PAL IIe with Disk II card and extended 80 column card and for an hour after arrival it was working fine including a self test, writing floppies with ADTPro, etc - it then froze when running ADTPro and hasn't worked since. A list of what I have done so far:
1. Power cycle after initial freeze (didn't respond to soft reset) resulted in a white screen, no beep.
2. Removal of 80 column and Disk II card resulted in beep and command prompt, froze shortly afterwards. Reboot results in screen of garbage.
3. Removal of power for a bit gets me back to 2. for a short while (~10 seconds) - sometimes it will start the self test if I do it but will never complete and will freeze at a random point.
4. If I reinsert the expansion cards it will get me back to 2. again for a short while, but will get the white screen instead of garbage on reset.
The random behaviour coupled with it sort of recovering after a power off led me to suspect the power supply - the RIFA filter caps were replaced before I got it, but there was a faint smell of burning when I opened it up after the initial freeze. Nothing seems to be visibly burned/bulging/leaking except for dark spots next to the large resistor adjacent to the transformer on the low voltage side of the PSU. Voltages coming from the PSU are all fine according to the multimeter.
Before concentrating on the PSU I put a multimeter in continuity mode across a few capacitors with C9 and C10 registering a beep (not really sure what I'm doing here so that might be normal).
It all points to PSU to me but would welcome any input!