miraco
Experienced Member
Hello everyone! I need some advice on my troubleshooting efforts to resolve a C64 black screen issue. The system board is one that I built using the BWACK 250407 board. It was fully operational for a few weeks and then started giving me the black screen. The dead test runs fine with no errors reported. The diagnostic cart just sits at a black screen. I am using replacements for the PLA and SID chips. Per the diagnostic manual I get these voltage readings on the PLA:
Pin 15 - 4.9V
Pin 16. - 2.2V
Pin 17. - 4.9V
The usual suggestion for these symptoms is a probable bad kernel rom. Since pin 16 on the PLA is the kernel rom select signal, this seems like a possible issue. Shouldn’t this be reading ~5V as the Basic and Character rooms read? I have three re-engineered PLA replacements that I have swapped out with no change in the result.
I would appreciate any suggestions on how to proceed with this .
Thanks - Mike
Pin 15 - 4.9V
Pin 16. - 2.2V
Pin 17. - 4.9V
The usual suggestion for these symptoms is a probable bad kernel rom. Since pin 16 on the PLA is the kernel rom select signal, this seems like a possible issue. Shouldn’t this be reading ~5V as the Basic and Character rooms read? I have three re-engineered PLA replacements that I have swapped out with no change in the result.
I would appreciate any suggestions on how to proceed with this .
Thanks - Mike