Better Video with a Commodore 16

Hello,

I was always annoyed with the video output of a C16. If you use a 
Chroma/Luma cable and hook it up to a 1084 monitor you can see why. 
Switch the monitor vom LCA to CVBS (the switch next to the cinch inputs) 
and the picture stays in color. I always thought that this is the fault 
of the RF modulator (since the signals are routed through it) but then I 
dug out my C116 board to test something else and noticed that here the 
picture turns black&white (as it should).

The reason is the layout of the C16 board, the traces that connect TED 
with the modulator run side by side for most of the way. That seems to 
be enough for the chroma signal to 'make an impression' on the luma 
signal. Whoever did that layout must have been in a hurry...

There is a simple way to fix that:

  - Remove all socketed chips from their sockets and store
    safely (black ESD foam works best). Remember which one
    of the 28pin chips goes where!

  - Remove the board from the case

  - Locate pin 13 on TED and use a circuit tester to
    find the other end at the modulator. Mark both pins.

  - Cut the trace starting from TED pin 13. This trace is
    located inside the TED socket on the component side and
    a bit hard to reach. A scalpel or similiar works. Ensure
    that you cut only this one trace.

  - Use the circuit tester to make sure the trace is cut.

  - Cut the trace to the marked pin on the modulator as close
    as possible to the modulator pin.

  - The trace has one via, use the circuit tester on that and
    the modulator to make sure this end is cut as well.

  - Now solder an insulated wire to TED pin 13 and the
    other end to the marked pin on the modulator. Keep the
    connection as short as possible.

  - Check for unintended shorts with other pins.

  - Make sure the insulation cannot be damaged by the sharp pins of
    of the CPU socket (tape is in place for example)

  - Put everything back together, make sure the chips are correctly
    oriented in their sockets.

    (Picture: 
http://www.retroisle.com/commodore/c16plus4/Pictures/images_c16/CBM%20C16%20PCB2.jpg 
)

The C16 should work as before, just with less video noise and switching 
to CVBS will produce a b&w picture.

  Gerrit



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