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Calibrating the Deinterlacer
The Deinterlacer circuitry samples in the A3000's native NTSC or
PAL output and scandoubles or deinterlaces it, outputting the new signal at
a flicker free VGA level.  In a way, it works very similarily to a Time
Base Corrector, commonly found in professional video studios.  

One issue that arises is calibrating the timing of this device.  If
the deinterlacer is ill-tuned, you'll see flickering specks on your
display.  It's very simple to adjust the unit, just use a potspanner, which
is a plastic screwdriver with a small plastic or metal tip, and insert it
into the hole on the rear of the A3000.  This hole is between the DB15HD
and deinterlacer toggle switch.  Twist the trimpot left or right to correct
the display.  When the pot clicks, you know you've turned too much.

There were calibration images from Commodore on the A3000
distribution, with a special one for PLL, but as long as it looks okay for
normal output, you're fine.

One mode that always looks weird is SuperHires, 1280x480.  This is
normal: the deinterlacer doesn't have the capability for such a detailed
mode, and has to skip every other line.