[PS1] Looking for Help Diagnosing Memory Card Port Issues on 5501 model Playstation

Hi y'all. I already posted this in the PSX subreddit, but I thought it would be best to ask here as well. I'm trying to diagnose a problem with this 5501 model Playstation I got on eBay recently. For the most part it works fine, including the controllers I've used, but it seems to not read my memory card out of either slot. It is an aftermarket memory card, but it works fine on my PS2 slim (it's kept a save of ff9 and a couple other games for several months). I've also tried replacing the memory card/controller piece with one I found on eBay that was said to be working, but that didn't fix the issue either.

At this point, I'm led to believe it's something to do with the main board of the console itself. However, all the usual suspects like the controller port fuses and diodes and capacitors all seem to be reading like I would expect them to on my multimeter. I'm at a loss and i wanted to know if anyone has had any experience with this particular problem. I'll be happy to share any further info if need be. Thanks in advance.