Osbourne OCC1 problem

[Philip Pemberton]

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/