14 Jul
2006
14 Jul
'06
7:35 a.m.
Jules Richardson wrote:
Dave Dunfield wrote:
Hmm, well no luck there - and everything seems tight in its sockets.
Swapping RAM banks doesn't help, either.
CPU reset and clock(s) seem OK on the 'scope. There looks to be activity on
the various RAM /CS lines, too.
One strange thing: I pulled the character generator ROM, expecting that doing
so would either give me a completely white or completely black screen. It
doesn't - I get some white blocks and some black blocks at random on the
display. I admit to not yet understanding what the PET's doing with its
display circuitry, but I had expected that having no ROM there would result in
every character having the same value, so regardless of what happened to be in
the video RAM at power-up I'd get the same character at every screen location.
Not sure if that sounds indicative of a particular fault...
cheers
Jules
Physical failures are common in the PET - look
for corroded sockets,
video, power connectors etc.
I didn't see anything first time around (re-seating ICs and connectors
was one of the first things I did), but I'm just going through it again
to be sure.