Battlezone Half Screen, 1N270 diode on X center?

Hello,

     I have a Battlezone AVG board that boots up fine and passes self-test.
After replacing several dacs, the board was working fine. Now, the right half
of the screen is missing, and I know the problem is not monitor related. The
rscreen was fine, and the right side just started gradually fading out, and
now just the left side is there. (these pics are big):

<A HREF="http://members.aol.com/mkdud/BZ/bzhalf.jpg">http://members.aol.com/mkdud/BZ/bzhalf.jpg</A>

     I just noticed that another working BZ AVG board that I have has a 1N270
diode that goes from where the X Center pot would be (kathode) to ground
(anode). Does anybody know what this diode does? The board that only shows
half of a screen does not have the 1N270, and it looks like it never did.
When were these added, and what for?

<A HREF="http://members.aol.com/mkdud/BZ/xctr1n270.jpg">http://members.aol.com/mkdud/BZ/xctr1n270.jpg</A>

     Also, why do some boards have mylar caps attatched to pins 1 and 2 of
the TL082s?

Please help if you can,
Thank You,
Michael Kelley

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Received on Sun Feb 23 18:11:55 2003