16 Apr
2012
16 Apr
'12
6:02 a.m.
On Sat, Apr 14, 2012 at 2:12 PM, Dave Caroline
<dave.thearchivist at gmail.com> wrote:
On Sat, Apr 14, 2012 at 7:52 PM, Win Heagy <wheagy
at gmail.com> wrote:
> Hi,
>
> I recently picked up a PET 2001-8. ?It has a video issue...see
> http://imgur.com/PKc97 ?(disregard the black diagonal scan
lines...digital
> camera artifact).
2 The processor cannot write to the video ram (and
therefore clear it)
>>That's also a distinct possibility.
>>Which version of Static PET do you have? They
came with different
>>types of ROM and RAM (the schematics for all three variations are
>>posted on zimmers.net). Main memory and video memory use the same
>>chips, 1Kx4 in pairs. You need two working chips for video memory at
>>at least 4 working chips for main memory (the first 1K is taken up
>>with zero page variables, stack, and tape buffers). 2114 SRAMs are
>>notoriously suspect, but 6550s can fail too.
Is it possible to tell the version by looking at the board? I posted a pic
at
http://imgur.com/3aeiL
>>Before worrying about RAMs, check your Vcc...
there are 4 regulators
>>and 4 legs of +5VDC. If you've lost one, obviously, it will act
>>strange.
I checked the 4 regulators and they are all outputting +5VDC. The most
deviation I saw was +4.94VDC.
Thanks...Win