I am working on an Atari middle earth, this is the first one of these I have encountered.
The audio and game functions work including switch operation, but I don't have score display or feature lights.
you can play the game without score or feature lights, the game logic seems to work fine.

What It seems to be linked to a secondary bus, it is enabled by the buss available signal from the cpu but I never get a ba from the cpu. I tried all the obvious like a bad cpu or a load on the ba line. It is on the DxB data lines and all 8 data lines seem active. but I never get a ba. Both the display and feature lights are controlled by the DxB data lines.
Any ideas?
btw: cpu does not lock up the functions that are being read and processed are working fine.

oh, just to add I replaced the eprom, and had a bad eprom and It miss read the instruction set and the feature lights came on, but not correctly, nor did the system work correctly(cpu lockup), but that told me that the bus b and most of the operation of buss b would work to some degree. I did get a good 2716 burnt and in the circuit and the unit is running as before with the original roms without the feature lights or scoring.

I was thinking that maybe the cpu is hung up on a feature not responding correctly on buss b.

ok, as an observation the address lines a0 through a3 control the "a" buss, and jointly a4,a5 control a and b buss and a6 through a9 are dedicated to b buss as long as I have a ba. data would go through.
what is interesting is the a4 and a5 will send address info to buss b without the ba. I wonder if the cpu program is pulling information on the b buss and using it as some kind of pseudo interrupt to tell the program to read or write data to b buss, maybe what ever is supposed to send data from these two address lines is not functioning.

Just a guess, I cannot know what the programmers had in mind when they made that system, this is why it is tough to fix this one.

instead of using 6821 pic controllers to communicate to the outside world they built their own interface for each type of communication. This machine is a customers of mine really all I need is the board. If you are willing to part it out I will take the main board but the whole machine does not have that great of value.
Otherwise I need to keep working the problem.