Commando bottom board issue (85605-B-1)

[jizzfu77]

Hi, my original commando pcb doesnt work with the bottom board connected (black screen, no sound, no activity), i have another commando bootleg board so i swapped the bottom board and it worked. I also tried to disconnect the bottom board and the game "works" but without sprites, then i tried the original bottom board on the bootleg one and same issue, black screen. I really want to fix the original one, someone can help me? Thanks!

 

[Lurch666]

When you say blank screen do you know if the game is active (data and clock on CPU) or is the bottom board stopping the game running entirely?

Could it be shorting?

 

[jizzfu77]

When you say blank screen do you know if the game is active (data and clock on CPU) or is the bottom board stopping the game running entirely?

Could it be shorting?

the voltages are ok, so i think no shorts...but maybe im wrong. The clock is present and i see some activity on cpu and ram.

 

[Lurch666]

If you are seeing clock and other activity then it's not a short.
Next thing to try is swapping the ribbon connectors just to see if the behavior changes.

If that makes no difference then you need to see if the bottom board is messing with any data or address lines. Check for activity on all the pins of 1D and 1C on the bottom board that are fed from the top board.

 

[jizzfu77]

If you are seeing clock and other activity then it's not a short.
Next thing to try is swapping the ribbon connectors just to see if the behavior changes.

If that makes no difference then you need to see if the bottom board is messing with any data or address lines. Check for activity on all the pins of 1D and 1C on the bottom board that are fed from the top board.


View attachment 37675

thanks! i'll check!

 

[jizzfu77]

checked ribbon cables and checked activities in 1c, 1d and 1e (ls245). All ok, also swapped the ribbon cables with the working bootleg...original still not working, bootleg works.