lroehrs
New member
- Joined
- Jul 7, 2025
- Messages
- 4
- Reaction score
- 1
I am currently working on a PP1 Boardset and get the following Behavior on CPU B:
After Powerup, Selfcheck etc. (Both CPU A and CPU B are lifted out of Reset) the Game does nothing (Not showing Diagnostics, the grid etc)
The Diagnostics may flash eventually but generally speaking the Boardset just Resets after a while (Watchdog is not working either but that is likely another thing)
My Issue is that NMI on CPU B is stuck low all the time (which also lets it become incredibly hot).
Ive already:
- Replaced the PAL @ 2N with a GAL16V8B programmed with the corresponding file from pldarchive as another Pin of it was completely dead
- Tried to Piggyback the 74LS74 responsible for the Signal
I get the following signals when measuring:
- NMIACK is toggled and then stays High during NMI Low
- VBlank is Toggling
- AD0B is Strobing
- 5V on all Pins of the 74LS74 where it is supposed to be
My Problem is that I currently dont have another working PP1 Boardset here to measure the correct Behavior on these Pins, can anybody point out where I should probably look next?
After Powerup, Selfcheck etc. (Both CPU A and CPU B are lifted out of Reset) the Game does nothing (Not showing Diagnostics, the grid etc)
The Diagnostics may flash eventually but generally speaking the Boardset just Resets after a while (Watchdog is not working either but that is likely another thing)
My Issue is that NMI on CPU B is stuck low all the time (which also lets it become incredibly hot).
Ive already:
- Replaced the PAL @ 2N with a GAL16V8B programmed with the corresponding file from pldarchive as another Pin of it was completely dead
- Tried to Piggyback the 74LS74 responsible for the Signal
I get the following signals when measuring:
- NMIACK is toggled and then stays High during NMI Low
- VBlank is Toggling
- AD0B is Strobing
- 5V on all Pins of the 74LS74 where it is supposed to be
My Problem is that I currently dont have another working PP1 Boardset here to measure the correct Behavior on these Pins, can anybody point out where I should probably look next?