Ape Cosplay
Enthusiast
Game had several faults:
- Doesn't boot = bad work RAM @16L
- No sound = corrosion on the sound ROM
- No text layer
The latter is the interesting part of the repair: the TA-16 PROM @21K had failed.
OG chip is a MB7114 (82S129 equivalent), unfortunately I didn't have a blank spare and my latests attemps of buying NOS chips resulted in receiving already programmed devices and those are OTP (One Time Programmable).
I decided to use a GAL16V8 instead, from the available dump I deducted the equations (only two outputs are used = D0 & D1, A3 and A7 not used either, CE1 and CE2 hardwired to ground = permanently enabled):
D0 = A0 & !A1 & !A4 # A0 & !A1 & !A5 # A0 & !A1 & !A6 # A0 & A2 & !A6;
D1 = A0 & A1 # A0 & A4 & A5 & A6;
It was also easy to retain the same pinout:
Pin 1 = A6;
Pin 2 = A5;
Pin 3 = A4;
Pin 4 = A3;
Pin 5 = A0;
Pin 6 = A1;
Pin 7 = A2;
Pin 19 = A7;
Pin 18 = CE2;
Pin 17 = CE1;
Pin 16 = D0;
Pin 15 = D1;
Pin 14 = D2;
Pin 13 = D3;
Insert the GAL in the socket, aligned pin 1 to pin 1 and leaving pins 9, 10, 11, 12 sticking out of it.
Only hack is to run a wire between pins 8 and 10 of the GAL to provide ground (disregard the ridiculously long yellow bodge wire, I made it nicer after confirming proper operation).
- Doesn't boot = bad work RAM @16L
- No sound = corrosion on the sound ROM
- No text layer
The latter is the interesting part of the repair: the TA-16 PROM @21K had failed.
OG chip is a MB7114 (82S129 equivalent), unfortunately I didn't have a blank spare and my latests attemps of buying NOS chips resulted in receiving already programmed devices and those are OTP (One Time Programmable).
I decided to use a GAL16V8 instead, from the available dump I deducted the equations (only two outputs are used = D0 & D1, A3 and A7 not used either, CE1 and CE2 hardwired to ground = permanently enabled):
D0 = A0 & !A1 & !A4 # A0 & !A1 & !A5 # A0 & !A1 & !A6 # A0 & A2 & !A6;
D1 = A0 & A1 # A0 & A4 & A5 & A6;
It was also easy to retain the same pinout:
Pin 1 = A6;
Pin 2 = A5;
Pin 3 = A4;
Pin 4 = A3;
Pin 5 = A0;
Pin 6 = A1;
Pin 7 = A2;
Pin 19 = A7;
Pin 18 = CE2;
Pin 17 = CE1;
Pin 16 = D0;
Pin 15 = D1;
Pin 14 = D2;
Pin 13 = D3;
Insert the GAL in the socket, aligned pin 1 to pin 1 and leaving pins 9, 10, 11, 12 sticking out of it.
Only hack is to run a wire between pins 8 and 10 of the GAL to provide ground (disregard the ridiculously long yellow bodge wire, I made it nicer after confirming proper operation).
