Sonic and Knuckles...graphic corruption, resets, and lockups

So while testing out a couple of Traco DC-DC buck converters in my genesis last night I discovered that apparently my Sonic and Knuckles cart doesn't like to play with Sonic 3 locked onto.

Both games will play fine by themselves, but when I attach Sonic 3 to Sonic and Knuckles, this is what tends to happen:

Starting up a game of Sonic 3 while attached to S&K will cause the game to lockup within about 60sec of starting. Doesn't matter what character you choose and it usually corrupts the save file requiring I delete it.
If it doesn't do that, then it will exhibit graphic corruption. Usually it will generate a series of missing sprite graphics as uniform squares on the screen. Doesn't always do this and the corruption will change and isn't ever the same.
If left on long enough trying to get through this, it will eventually start to reset the game back to the Sega logo and back to title screen. Within a min or so of this, the game will reset after displaying the Sega logo and continue.

So I thought the DC - DC buck converters might be the issue, so I reinstalled the 7805s back in place and back onto the heatsink. Nope...S&K with Sonic 3 attached still does the above regardless. I also replaced the 47uf 16v cap in the Sonic 3 cart in case that was part of the issue. No change.

Again, it would seem both games by themselves will play just fine. Though I did get a lockup in Hydrocity when playing Sonic 3 by itself. But this was much much later into game play. And my Sonic 3 has always been a bit of a toublemaker on my va2 HDG.

Ideas or has anyone ever seen anything like this? All other games I play on this system seem to work just fine without issue. I didn't test Virtua Racing but I probably should tonight. Also while I haven't tested lately, Game Genie use was never an issue either. So...yeah...

Have you by any chance cleaned the slot on Sonic & Knuckles?

yes...I did that last night. But I haven't really hit with my concentrated contact cleaning solution yet either. Was going to try that tonight. I'm thinking that I've always had goofy issues with this S&K cart since I bought it used back in the early 2000's.

An update to this. So in another thread here about CPU overclocking, I stated that I had been unsuccessful in just even getting other variants of the 68k to work on my Genesis. I was testing with the use of a 64pin socket that I installed to make CPU changes easier.

Well last night I began to notice that if I applied slight pressure to the CPU while running Sonic 3 or some variant of Sonic 3 along with S&K. That I could usually get a decent stable picture and have it run more reliably with the lockups. Take my finger off and they would eventually the issues would come back. So first thing I did was retouch all solder points on the bottom of the PCB with a little more solder in case something wasn't making good contact with the socket. That didn't help in the slightest. So I removed the socket completely and began to look at the traces in detail.

This was the "eureka" moment. It would appear that several of the traces on the CPU have connection points on both sides of the PCB?! So with the socket in place, I can't confirm that connections required on the top layer of the PCB are even being made since the socket covers them up. I went ahead and reinstalled the original Signetics CPU by soldering it directly to the board but only soldered from the bottom of the PCB as I did originally with the socket. Tested Sonic 3...etc and still had occasional issues but much less so. I then touched up all the pins on the CPU with some solder on the top layer (As many as I can get to without possible risk of damage to the cart slot), and for the first time in quite some time, I was able to have Sonic 3 while locked onto the S&K cart running in demo/attract mode for about 3 hours without any issues. I was then able to play for well over an hour as Knuckles on a game of Sonic 3 with out any issues. I did see one graphical glitch briefly at the beginning of the game and it quickly went away after the screen scrolled a bit and never came back.

So...yeah... guess the CPU at least on a va2 model 1 requires connections on both top and bottom of the PCB to reliably work. I only have one other console this picky...my Vectrex. I haven't fully test it with it attached to the SegaCD and the 32x on it but will do so in the days and weeks to come.