TRS80 Model 4P gate array help

From: Keith Whitehead <K.J.Whitehead_at_massey.ac.nz>
Date: Thu Mar 12 22:54:28 1998

Ok...here's the problem
The machine come up with garbage on the screen.It would also seem that the
video is inverted, I can see the retrace lines etc, so the horizontal
blanking is not working either by the looks of it.

What I suspect is wrong is that either U42 (the 6845 labeled in my machine
as a motorola SC80757P) or U102 (the 4.3 video support chip) is faulty (or
both?).

Does anyone have any info on U102 (what is it..can I get another?) or any
other thoughts.

Some other notes are.
1. It seems to boot (I get a very crappy tandy logo in inverse on the
screen) though the screen is so unstable as to be unreadable.
2. It does not matter if it is in 64 or 80 column mode, the video is still
crap.
3. I suppose the Char generator rom could also be a problem

Any help would be appreciated. BTW does anyone have the diagnostic disc for
the 4/4P ?


Cheers

+----------- Keith Whitehead -----------+
| Physics and Chemistry Depts |
| Massey University |
| Palmerston North |
| New Zealand |
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| Ph +64 6 350-5074 Fax +64 6 354-0207 |
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Received on Thu Mar 12 1998 - 22:54:28 GMT