As mentioned in Body pops thread about his sprint issues I'm also trying to fix one of these PCBs.
Mine is just not running code and it's watchdogging but it is displaying garbage so the video is functioning.
Have replaced the old CPU socket,checked the ram,all the ttl dealing with the CPU address and data lines and the LS04s that invert the data comong from the ram.
I have also verified the prom at E2 but cannot check the 9301 at F2 because at some point the legs were cut off then resoldered on so my slice clip won't fit.
I don't have spare 9301 so built an adapter to use a 7442 to replace it but it made no difference.
One thing that's puzzling is I don't see any activity on pin 11 of the 9301 (prom 3 signal) but I don't know if that's just down to how the code is jumping since if I remove all the program roms it starts to show activity.
Since the program roms are completely none standard I made an adapter so I could read them as 2716 and roms 1-3 are ok but the fourth rom at E1 showed bad code in some places so I rebuilt the adapter so I could use a 2716 to replace the rom at E1 but that still didn't get the code running.
Next I wrote the code for rom 1 onto a 2716 and replaced that rom with my adapter then connected my slice to the 2716 to see what was happening and it's showing errors reading the rom so now I'm thinking there's either a timing issue or contention on the data lines.
I'm reading the manual now to see if I can figure out how the ram/rom timing works but any suggestions on where to go next would be appreciated.
Mine is just not running code and it's watchdogging but it is displaying garbage so the video is functioning.
Have replaced the old CPU socket,checked the ram,all the ttl dealing with the CPU address and data lines and the LS04s that invert the data comong from the ram.
I have also verified the prom at E2 but cannot check the 9301 at F2 because at some point the legs were cut off then resoldered on so my slice clip won't fit.
I don't have spare 9301 so built an adapter to use a 7442 to replace it but it made no difference.
One thing that's puzzling is I don't see any activity on pin 11 of the 9301 (prom 3 signal) but I don't know if that's just down to how the code is jumping since if I remove all the program roms it starts to show activity.
Since the program roms are completely none standard I made an adapter so I could read them as 2716 and roms 1-3 are ok but the fourth rom at E1 showed bad code in some places so I rebuilt the adapter so I could use a 2716 to replace the rom at E1 but that still didn't get the code running.
Next I wrote the code for rom 1 onto a 2716 and replaced that rom with my adapter then connected my slice to the 2716 to see what was happening and it's showing errors reading the rom so now I'm thinking there's either a timing issue or contention on the data lines.
I'm reading the manual now to see if I can figure out how the ram/rom timing works but any suggestions on where to go next would be appreciated.
