belzrebuth
Member
- Joined
- Jun 25, 2021
- Messages
- 30
Hi all,
first post here.!
I've got a Commodore Pet 2001 (model with 2114 ram ICs and 2316B ROMs pcb v.320137).
The unit was in bad shape very dirty and the fuse was blown.
The power cables to the PCB were not crimped to a connector but soldered in place and the 4th wire of the PCB power connector has broken off touching the 5th wire.
That was probably why the fuse was blown.
Cleaned a bit and powered it on to be greeted with a garbage screen.
The previous owner said even when the fuse wasn't blown he was still having a garbage screen.
So the power accident might have only made things a bit worse.It shouldn't be the root of the problem.
I've checked the 5V power rails and they're good.
Then I breadboarded a 2114 RAM tester (the one with the arduino nano) and 3 or 4 RAM ICs came out bad.
That's okay cause we don't need ALL the RAM to boot.
Then I used my TL866 programmer to read the 2316B ROMS (trick with the hex inverter to treat it as a 2716)
All the checksums of the ROM binaries are ok according to the files at zimmers.net.
Next I tried a minimal configuration (only 4 good RAM chips on the first 4 right positions) and 6522/6520 removed.
Still garbage screen/no boot.
One clue is that the resistance to ground of the first top left 7805 is about 400 Ω which is a bit low compared to the 2nd and 3rd which are about 2k.
The 4th is also a bit low at about 1k.
As I understand all 7805 output legs should be around 1.5-2k to ground.
Any suggestions on how I should proceed?
first post here.!
I've got a Commodore Pet 2001 (model with 2114 ram ICs and 2316B ROMs pcb v.320137).
The unit was in bad shape very dirty and the fuse was blown.
The power cables to the PCB were not crimped to a connector but soldered in place and the 4th wire of the PCB power connector has broken off touching the 5th wire.
That was probably why the fuse was blown.
Cleaned a bit and powered it on to be greeted with a garbage screen.
The previous owner said even when the fuse wasn't blown he was still having a garbage screen.
So the power accident might have only made things a bit worse.It shouldn't be the root of the problem.
I've checked the 5V power rails and they're good.
Then I breadboarded a 2114 RAM tester (the one with the arduino nano) and 3 or 4 RAM ICs came out bad.
That's okay cause we don't need ALL the RAM to boot.
Then I used my TL866 programmer to read the 2316B ROMS (trick with the hex inverter to treat it as a 2716)
All the checksums of the ROM binaries are ok according to the files at zimmers.net.
Next I tried a minimal configuration (only 4 good RAM chips on the first 4 right positions) and 6522/6520 removed.
Still garbage screen/no boot.
One clue is that the resistance to ground of the first top left 7805 is about 400 Ω which is a bit low compared to the 2nd and 3rd which are about 2k.
The 4th is also a bit low at about 1k.
As I understand all 7805 output legs should be around 1.5-2k to ground.
Any suggestions on how I should proceed?