Battlezone centering

Just in case Matt McCullar forgets, this is what he posted to RGVAC
regarding centering pots on a Battlezone board.

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I'm not 100% certain about this, but I'm looking at a _Battlezone_ board
and _Red Baron_schematics.
  
It looks like Atari did plan to include X and Y centering pots during
the engineering stage; why they left these out, I don't know. But it
appears easy enough to add.
  
X channel first.
The pot value at R101 (XCENTER) should be 50 k.
You must also add a 0.1 uF cap at C102.
Also add a 220k resistor at R100.
  
  
Now for the Y channel.
Pot value at R91 (YCENTER) should be 50 k.
You must also add a 0.1 uF cap at C101.
Also add a 220k resistor at R90.
  
And that's it.
What you're essentially doing is adding a DC component to the output
signal. The pot's leads are connected to +15v and -15v, with the wiper
in the middle mixing in the voltage-divided signal with the video signal
at the final op-amp output.

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tom :^)
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Received on Fri Dec 15 17:52:58 2000