18 May
2008
18 May
'08
4:07 p.m.
Philip Pemberton wrote:
Something in the video generator circuit on the
digital side by the
looks of things. Probably pre-character-generator -- those characters
look fine and they're in the right place, but they're the wrong
characters. So that's anything pre-character-generator basically --
buffers, latches, RAM, not necessarily in that order.
I've just seen the MPEG -- looks like what you're seeing is the counter (or a
latch, flipflop or buffer) sticking. It's holding an address for a few
characters instead of a single character period.
If you run the video frame-by-frame, you see it displaying:
Loading CP/M and HELP...
which turns into
LLLLLnnnnn////nd HHHHHH.......
or something to that effect - the video isn't fantastically clear.
So you want to look at:
- counters
- buffers / flipflops / latches
- latch / enable logic for the above
That's on top of checking the PSU as I mentioned in my last email.
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/