40-col PET video adjustments/problems?

From: Ethan Dicks <ethan.dicks_at_gmail.com>
Date: Tue, 29 Sep 2009 22:05:48 -0400
Message-ID: <f4eb766f0909291905u23bc3611l780196f1301b584@mail.gmail.com>
Hi, All,

I'm in the middle of resurrecting a Static PET board (that I got last
year from MH Stein in (pre-warned) sad shape).  I don't have an
original PET chassis at the moment, but I do have several enclosures
for 2001N/3032 16K/32K PET boards (pre-CRTC).  The enclosure I'm
working on has a monitor that works perfectly with the 3032 board
Anders Carlsson sent to me at Pole.  When I plug in the Static PET
board, I get characters, but not with the same "spread" across the
CRT.  I see 25 rows, but they are about half as tall as I'd expect
(with large blank spots above and below).  I do not, however, "see" 40
columns.  I see more like 25-30 columns, then the brightness of some
of them suggests to me that the remainder are "folded" under the
visible ones - a common problem back in the day with wonky video.  The
chars are all sharp and stable - no tearing, no walking, no wobbling -
just not 40x25 filling most of the tube (unlike the perfect view with
the 3032 board).

There are only two potentiometer adjustments on the monitor board -
brightness and V.Height.  Both do the expected thing.  I can crank up
the height with the 2001-8 installed, but then the 3032 display is way
too "tall".  I can't fix the width or the H.Pos or whatever it is that
is causing the issue with the columns.

I would expect that if there were a severe problem with the video, I'd
get sync problems or tearing or snow or pixel garbage.  There's none
of that.

I've looked around a bit, but the diagnostic information I've found
stops before the component level.  Does anyone know of any in-depth
video repair info?  I can't imagine there's a problem with the video
board since the 3032 display is flawless - am I wrong in thinking that
the video outputs from the 2001-8 and the 3032 are compatible if not

Does anyone recognize these symptoms?  Has anyone done chip-level
debugging of the video circuit on a pre-CRTC PET?  I have the
schematics, naturally, but since so much works, I'm not sure where to

Thanks for any suggestions.


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Received on 2009-09-30 03:00:04

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