Hack: X- and Y-invert on the motherboard...

...rather than futzing about with the monitor yoke. My situation:
Quantum, running on a horizontally-mounted monitor. The good news
is that (for this monitor) swapping the X and Y outputs produces a
full picture. The bad news was that the X output (relative to the
horizontally-mounted monitor) was inverted right-to-left, and that
unlike Tempest, there are no XINVERT and YINVERT pins on the board
to tweak.

According to the datasheet for the LF13201 analog switch (from the
spies.com archive) and the schematics for the board, it looks like
most, if not all, of the Atari games that use this chip in the AVG
section of the board are using it to control inversion. The axis-
inversion signal (and its inverse, from a nearby NOT gate) go to a
pair of switches on the LF13201; the configuration of the switches
determines whether the output signal is inverted or not.

On Quantum, the signals controlling the switches are on pins 1 and
16 of the LF13201s. Swapping these pins (cut two traces, solder a
pair of jumper wires crosswise) inverts (logically) the meaning of
the onboard X- or Y-invert signal, inverting (at the op-amp and on
the screen) the orientation of the video output.

In my situation (rotated monitor and X/Y swapped), the two pins to
swap surfaced at two adjacent vias (thru-holes) near the three VRs
just above the AVG portion of the board, allowing me to stick a 2-
pin .100" connector into the board and "connectorize" the hack for
easy reversibility should I ever plug it into an original cabinet.

(...and allowing me to post to vectorlist in bricktext. Woo-hoo!)

I can't take full credit for this hack - according to:

http://x32.deja.com/=dnc/[ST_rn=ps]/getdoc.xp?AN=107601739

...it looks like Ray Ghanbari thought of this first, though he was
running horizontally-mounted games on a vertical monitor. Like he
suggests, check against your schematics first before trying it.

Later,
Doug.

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