I am now a supreme noser. To recap, here’s the last graphics issue I was trying to fix:

Notice the Q*Bert logo in the top left, and the screwed up sprites. Here it is working:

There seems to be a sound issue that only occurs when you make Coily jump off the board after you. You can here it twice in the video above. If anyone knows what would cause that, please let me know.

The graphics problem ended up being a bad jumper on the main board, JP13:

Before finding this, I figured I should go through all the boards in the game to make sure there were no issues. I started with the filter board, which had some major issues. One of the header pins burned up, and left a crater in the board:

Both pins on the right were affected, and consequently some rocket scientist soldered the two wires that connect to those pins right to the back of the board:

I removed that set of header pins:

and replaced them with a new set:

Around back, you can see the remnants of the wires they soldered directly to the board:

The pin to the right of the fried one actually still had its solder pad and trace in tact, so I only needed to solder in one jumper directly to the header pin:

I resoldered all the other header pins on the board. I then pulled the main PCB, and changed all the sockets. I did the same for the sound board, and replaced all the caps on it. That’s where I’m at now. I just got a replacement coil for the knocker. With any luck, maybe I’ll get that going tonight.