Commodore PET 2001 Video Problem - test-drb@ccmp.vtda.org

20 May 2012

Original Message:
Date: Sat, 19 May 2012 21:23:38 -0400
From: Win Heagy <wheagy at gmail.com>

...
  I've made a bit of progress on this since the last
post and wanted to get
 some additional help if possible.  I picked up a PETvet board from
 bitfixer.org and installed it.  The 2001 boots now (usually) and I get a
 screen like this.... 
http://imgur.com/fQxH3

...
  The machine works like this, but obviously the
vertical lines are a bit
 annoying.  The PETvet replaces the RAM and ROM, but does anyone know if
 that includes replacing the video ROM?  Any next steps are appreciated. 
...
  Thanks, 
...
  Win ------------------
No, the PETvet does not replace the chracter generator or the video RAM.

This one's easy:
Your problem is a bad CG or shift register; you don't say which model this
is, so, assuming one of the models using a 6540 ROM:

- Check that pin 24 of the IC at A2 is not broken or bent.
- If it's OK then either carefully bend out pin 24 or, preferably, remove or
bend out pin 24 of an IC socket and sandwich it between the chip and its
socket.
- The screen will probably look the same.
- Using a pin and a jumper, ground pin 24 of the socket (not the bent out IC
pin); if the screen stays the same it's the SR, if the lines disappear it's
the ROM.

- If it's an old model using 2316s then it's pin 11 instead of 24.
- If it's a dynamic RAM model using a 2316 then it's pin 11 of IC F10.

If you need a replacement for the ROM, ask on the Vintage Computer Forum;
someone will be able to fix you up.

mike