daver2
10k Member
Can you post a video of what you think is wrong?
A zoomed-in photograph would help if you can't post a video.
Dave
A zoomed-in photograph would help if you can't post a video.
Dave
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Commodore PET 3032 fast vertical sync.
- Thread starter Arn_K
- Start date
daver2
10k Member
I just looked in my PETTESTER manual...
Let's not jump to conclusions that something is faulty before we have investigated a bit more...
0010 0000 should be a [space] character. The entire screen should be blank in this case. Did you remove the 6502 CPU?
0100 0000 should be a 1-pixel thick horizontal line.
If you try 0010 0001 this should be a stable '!' character.
I think I have worked out why you may have upper-case letters instead of lower-case letters. Especially if the 6502 CPU has been removed (which may have answered my own question above). The character generator has two sets of character codings within it. The GRAPHIC signal switches between the two sets. If the CPU is removed, the GRAPHIC signal will be floating and will select the secondary character set. However, floating may result in some random effects? You could try the same test (0010 0000) with the CPU installed to see if you get a more stable result).
Dave
Let's not jump to conclusions that something is faulty before we have investigated a bit more...
0010 0000 should be a [space] character. The entire screen should be blank in this case. Did you remove the 6502 CPU?
0100 0000 should be a 1-pixel thick horizontal line.
If you try 0010 0001 this should be a stable '!' character.
I think I have worked out why you may have upper-case letters instead of lower-case letters. Especially if the 6502 CPU has been removed (which may have answered my own question above). The character generator has two sets of character codings within it. The GRAPHIC signal switches between the two sets. If the CPU is removed, the GRAPHIC signal will be floating and will select the secondary character set. However, floating may result in some random effects? You could try the same test (0010 0000) with the CPU installed to see if you get a more stable result).
Dave
I think there was a bad connection when testing 0010 0000, this now results in a blank screen.
0100 0000 is showing those lines, so they should be working too
And 0010 0001 results in an "!" character.
In that case, everything after the Vram chips could be fine.
I could redo the test with the CPU installed, but I think it is safe to assume the circuity after the Vrams is working.
0100 0000 is showing those lines, so they should be working too
And 0010 0001 results in an "!" character.
In that case, everything after the Vram chips could be fine.
I could redo the test with the CPU installed, but I think it is safe to assume the circuity after the Vrams is working.
daver2
10k Member
I agree.
It wouldn't hurt to try with the CPU in. We will need it in for my next test anyhow... You never know, it may show us something we didn't expect...
I am watching the Simpsons, and then going to do my 'chores' and then I can get back to your problem.
Remove your bodge resistors and reinstall the video RAM.
Dave
It wouldn't hurt to try with the CPU in. We will need it in for my next test anyhow... You never know, it may show us something we didn't expect...
I am watching the Simpsons, and then going to do my 'chores' and then I can get back to your problem.
Remove your bodge resistors and reinstall the video RAM.
Dave