TECH FIX: Cine AA VectorBeam Monitor (and a little story)

When I started collecting the first deal I made was with
Dave Whitman in NC. I drove a cube van down there from
Ottawa and picked up five VECTOR games. Luckily for me
I had business in RTP and convinced my management that
the cube van rental would cost the same as the return first class
air tickets. That was two years ago.

Since then the Asteroids, Asteroids Deluxe, Battlezone,
Armor Attack UR have been working on and off but for the most
part were all easy fixes (LS191 counters in the Asteroids, ROM
reseating in the AST DEL, cap kit in the BZ and ROM reseating,
and power supply repair (723) in the AA).

The fifth game was a Armor Attack CT which he gave me for
$50US (complete with extra boards but not working). This has been sitting
in my
basement for all this time and was dead until a couple of days
ago. Cosmetically it is very nice (8+/10 with some glass scratches) and
since I had never seen one
of these before it seemed like a good deal (similar one on Ebay recently was
about $600US??).

SYMPTOMS: No picture. CPU board known good. PSU tested good.

Fix #1: Replaced blown 47ohm resistor and 2n5320 in vertical drive (R118,
Q108).
Fix #2: HV supply needed replacing (no voltage).
        Now I get a long (length-wise) line on the display) => vertical
deflection
        still not working.
Fix #3: Replace heatsinked power transistors 2N5878/76 and pre-drivers
2N5320/22.
        [Unfortunately these tested well in and out of circuit and were only
found bad by
        guess-work and substitution]. :-(
        Now I get a half-screen (top only) squished squiggly picture (made
of segments) which
        seemed correct horizontally but zigged-zagged vertically downwards
from the drawn object.
Fix #4: Now I get the scope out and check the DAC output at the TL081s. I
        see a perfect copy of the game in XY-mode (comparing outputs of
TL081s) so I know the DACs/analog switch
        and op amps are working OK. Using XY-mode to debug an XY monitor
... go figure?
Fix #5: I go to the collector of Q104 (vertical) and keep the scope in XY
mode (knowing
        that the horizontal circuit is OK). And the scope shows me the
exact image that
        the monitor is displaying (though R-L inverted). Woo hoo!!
Something is wrong at this part of the amplifier.
        NOTE: Schematics note that shown waveforms at TL081/Q104 etc are
with Yoke removed ... I didn't bother doing that.
Fix #6: Replace Q104. Tweak the gain and linearity POTs. Now she works
perfect!!

SUMMARY: Using the oscilloscope through the circuit in XY mode might help
you to
debug the monitor faster than a one-by-one point-by-point pin-by-pin
analysis.

Turned out to be a pre-Xmas present to myself (two years after the fact I
guess).
I hope this helps someone else fix their VectorBeam/WG XY monitor one day.

SPW
Kanata, On
CANADA

p.s. The CT monitor is nice a crisp on all drawn vectors. My UR monitor,
however,
has the player tanks kinda fuzzy. Any ideas what causes that? The text
and 'copter
are cleanly drawn.
Received on Tue Dec 21 13:01:50 1999