Mac Classic: Sad Mac only when Ram Expansion card inserted

[jmb2011]

So got a replacement classic board in. Everything on it works great, however, when I plug in a ram expansion card (with 2x1mb sims installed) I get a sad Mac. Unplug the expansion card, boots with no issue.



What I’ve tried so far:
- Unplugged additional sims and change the jumper to no simms installed
- Plugged in another ram expansion card from working Mac classic
- Plugged this ram expansion into another known good classic (worked without issue)
- ran continuity test on all traces I could follow under the board

I’ve narrowed it down to an issue the logic board has with ram expansion cards. Also the logic board has been most likely recapped as the board has been cleaned and the caps aren’t original and one is a tantalum.

Any ideas of what to try next?

 

[robin-fo]

Did you set the jumpers correctly on the RAM card?

 

[jmb2011]

Did you set the jumpers correctly on the RAM card?

Yes, the jumpers are set correctly on the card itself

 

[SuperSVGA]

It looks like it was probably trying to write 0x00100000 to location 0x00100000, but it read back 0x00FF00FF instead. There may be an issue with accessing the lower byte of the RAM on the expansion card, for example a select line that is not making it from the CASPAL to the expansion card.

 

[jmb2011]

Wanted to update this thread. I sent this Logic Board into Amiga of Rochester for help. He was able to get it figured out for me. Two resistors turned out to be fried.