I agree with CP above and will add;

U2/3 are rules for the game, obviously, there's a conflict when the circuit lines are completed.

Assuming the MGoW is a functioning game, go over your work on the U2/3 conversion, look for a solder bridge where one shouldn't be. Also, if this is the first gen board, there should be 4 jumpers and a few traces cut on it to convert it to a second gen. If the conversion was done by you, you'll have to look it over too for an error.

Steve

Another shot in the dark, have you tried adding a pull up resistor to the CPU board? Below is a quote from Ed at GPE that he posted in another thread a while ago. It's possible that you may need this resistor installed.

Steve

"Small resistor on the plug into TC1 -- pullup resistor of 3.3K to the Read/Write signal. Some MPU boards run fine without it, some will kind-of work without it, and some refuse to work at all without it.
So... if you leave the connector on the TC1 40-pin DIP and unplug the 7-pin connector from the reset board - does they work then?
If it does work, you need to add a 3.3K resistor to bottom of TC1 between pins 7 and 11 and then leave the plug off of TC1. GPE"