OK,
This is a board from hell. Not sure what happened to it but it HAD to be a power surge of some kind.
Symtpom: Graphics corruption. Foreground AND background.
EPROM C26 was bad. Replaced.
Signals on the address lines of C11 to C18 were incorrect. Replaced F15 and F16
Working backwards from the outputs I found:
Output pins stuck on MOST LS157 ICs. Replaced C17, D17, E17, D16, and A4
Output pins stuck on D11, E11, E12, G12, E13, F13, G13, and F14.
Pins racing on D9, E9, E10, H10, and J10.
All of those chips tested bad on my EPROM programmer. EEEK.
Now I have graphics but have some sparklies around border graphics and a missing title screen to track down. It appears that C20 and C24's OE* lines are not going active. I already replaced the LS139 at D11 and the LS273 at D9. This last bit is frustrating.
RJ
This is a board from hell. Not sure what happened to it but it HAD to be a power surge of some kind.
Symtpom: Graphics corruption. Foreground AND background.
EPROM C26 was bad. Replaced.
Signals on the address lines of C11 to C18 were incorrect. Replaced F15 and F16
Working backwards from the outputs I found:
Output pins stuck on MOST LS157 ICs. Replaced C17, D17, E17, D16, and A4
Output pins stuck on D11, E11, E12, G12, E13, F13, G13, and F14.
Pins racing on D9, E9, E10, H10, and J10.
All of those chips tested bad on my EPROM programmer. EEEK.
Now I have graphics but have some sparklies around border graphics and a missing title screen to track down. It appears that C20 and C24's OE* lines are not going active. I already replaced the LS139 at D11 and the LS273 at D9. This last bit is frustrating.
RJ
