Sega Genesis 2 Bad Port/Logic - Right Direction Stuck

[Danexmurder]

I'm having trouble with a Genesis 2 that I am restoring. I'm really stumped with this one and haven't been able to track down much in the way of good info. I've gotten a couple replies over at r/console repair on reddit but I thought I'd ask the pros here.

Everything on this console works great and I was preparing it for an RGB mod but I discovered that the right direction on the second player port is stuck. This is indipendent of the controller.

First thing I did was check voltages on all of the lines and they are consistent with other model 2's that I have.

I figured that it could be a bad EMI Filter so I went ahead and replace all the 222 filters. I didn't try to 271s but I may do that next.

The resistors that feed into the EMI filters all check out.

I'm starting to wonder if something is up with IC6. I know it could potentially also be IC 4 or 5 since they also handle I/O.

Am I missing something. Has anyone else here successfully fixed one of these stuck button issues? I've seen a couple posts where people have talked about having the problem but I've never seen a post about it being solved.

I don't have a scope to test with but I have been using my multimeter to pretty good effect. Kinda cool seeing the voltage drop from 4.97 to 0 whenever you press a button. I'm still a little foggy on how this all works though. I understand that some of the buttons share a line and change depending on the state that the select line is in. I don't exactly know how to test this though. I can see proper voltage drops on up/down/a/start but I have yet to be able to see voltage change on any other line in from the port. I wonder if this is a multimeter setting issue.

I'm Trying to learn more about this. If anyone has any ideas I sure would appreciate some help. I hate the idea that a board that is otherwise in great shape will always have this defect that disables player 2. Thanks!