I've got a CBM 8032 that powers up "fine", but the screen is filled with
"!" on
every other character position. When some letters are repeated, they can change,
i.e. "nnnn" becomes "onon" which seems like (without checking the
ASCII charts)
that the "n" and "!" are ORed to become the "o". Anyone
have any ideas what the
problem might be? Most of the schematics I have are buried someplace, so I
thought I would start here.
When you say "powers up fine", do you mean:
- Powers up and runs - ie, even though the screen is garbled, you can see characters
changing where the ready prompt would be if you press RETURN a few times. (in
this case - according to your description, you should see every other character from
data output to the screen?)
- or -
- Powers up and does not catch fire, smoke, blow fuses, but otherwise does not show
signs of life.
If the former, then cause is most likely display RAM - I've had display rams go in a
couple of PETs over the years (iirc they are 2114s).
If the latter, the problem could be that the CPU is not getting far enough to clear the
screen or going haywire and overwriting the screen at some point in the startup
process. Standard debugging - I've had bad DRAMs, ROMs and the odd buffer
chip fail in various PETs at various times - shouldn't be too hard to track down.
Dave
--
dave06a (at) Dave Dunfield
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