While troubleshooting a narrow body E2209-44 machine that threw a malfunction code, I discovered an odd checksum on a 659183 P1 chip ending with 20. Replaced it with a different P1 chip, now the CPU is fully functional. The P2 chip on this machine is a 000900. This slot, as I'm told by Barry at Foxslotts, uses unusual and proprietary EPROMs, no data available. I can find no reference to these EPROMs anywhere, as the E755 chips are numbered -64, -65, and -66. All of the E machines I have use -80, -47, -48 and/or -102 M chips plus various 2701 and 3701 P2 chips.
Trying to find a pattern with the data in the Bally EPROMs. After looking at dozens of them, I have concluded that, in summing the data, the checksums on each have a distinct footprint that can't be changed. I have reason to believe that any deviation whatsoever in those checksums will result in an error code, preventing power-up.
M1, M2, M3 and P2: All checksums end in 00 (least significant bits), so typical checksums would be AF00 or something.
P1: always ends in 56, typical checksum would be 2F56 or something similar.
EDIT: I did find one P1 chip whose sum ended in 60 instead of 56 and is fully functional on a machine I have. Now I'm totally confused.
Can any of you Bally experts shed some light on this?