19 May
2012
19 May
'12
6:35 p.m.
On Sat, May 19, 2012 at 9:23 PM, Win Heagy <wheagy at gmail.com> wrote:
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
You are quite close now.
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.
Your video (character generator) ROM is likely just fine. It's more
probable that you have a either a bad video SRAM or perhaps a stuck
bit on the shift register that takes the byte from the ROM.
What does the screen look like if you remove the ROM? Do you still
see the lines? What if you swap the RAM chips. Does the vertical
line move?
Since you pulled your RAM for the PETvet, you should have spares to
try in the video RAM spot. I've seen up to 25% bad SRAMs in old PETs,
so it's a place to focus your efforts. If you can borrow or have a
spare character generator ROM, it's worth swapping that out, too.
I think you've got it narrowed down to one of 4 chips... ROM, RAM, or
shift register. The most likely candidate is RAM, in my experience.
-ethan