Testing XY games on oscilloscope

I do almost all of my board testing on the bench now with either a small
5" tv for raster games or an oscilloscope for XY games. I try to use up
as little space as possible.

I have one question about using the oscilliscope with XY games. My
oscilloscope has a Z input as well as an XY. When I hook up the Z probe
to the game the display goes completely blank. My roomate suggested that
I probably need to invert the signal in order to get the display I'm
looking for, which is the game without the retrace lines. He says that it
should be relatively simple to invert the signal with a transistor and
maybe a couple of resistors.

So - again - before I reinvent the wheel - does anyone already use a
device that does this? Maybe some kind of inverter with a coax connector
- or does anyone have something they've already tried in terms of removing
the retrace lines on an oscilloscope?

The main reason I want this is so that I can read errors during the built
in self tests.

Thanks....

Matt

                              V E R I O
             Orange County . Los Angeles . San Diego
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Matthew J. Rossiter email: mrossiter@verio.net
Customer Services Engineer http://socal.verio.net
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Received on Thu Nov 18 04:35:07 1999