My Packard Bell PB88M has generally worked for over a year but I've run into an issue with it that causes it to act like it's completely dead. There was battery damage on the backplane that caused the floppy controller and the serial/parallel ports not to work, but otherwise the system would work. But now all I get is power and nothing else. Here's what I've tried up to this point:

I've tried moving the CPU card (which is pretty much like a motherboard on an ISA card) to multiple different slots with no change.
The voltages on the power supply are good but there is a vdroop of 0.1v on the +5v rail at the expansion cards. I had the PSU +5v set to 5.26v at the molex connectors previously to get my XTIDE card to work properly. I also tried another PSU with no change.
I tried starting the system with just the CPU card installed (the machine would beep complaining that there's no CGA video card if the CPU card was working).
I tried using a POST card (similar to this: https://www.sintech.cn/post%20card/st8667%20P … est%20card.html) to see if there was activity. There seemed to be, but there were no POST codes displayed.
I've reseated the few socketed chips on the CPU card with no change.

This leaves me in a situation where it's either the backplane or the CPU card causing the issue, neither of which I can easily find a replacement. A part of me thinks that maybe I could try the CPU card in a standard motherboard with its CPU removed, but I don't know if I might break something trying this. Hopefully I can be led on the right track to get this rare computer running once again.