> I have a C64 with a 326298 Rev A. mainboard. As you know, this
> particular mainboard has the 5-pin A/V connector. What I would like
> to do is get S-Video output from this machine. 

Hi Larel,
     There are two ways to do it. The easiest is to use the composite
signal pin 4 for chroma, and luminance out of pin 1. The b/w signal
on pin one is wide band in the early board same as the later ones.
The quality of the display depends on the monitors ability to filter
the chroma out of composite but I've seen some pretty good results
with that method.
     A more professional way is to separate out the chroma directly
from the VIC chip at pin 14 and use a cap and resistor to tie it to
one of the A/V pins. I went whole hog and changed the socket on my
old board to an eight pin and used one of the two top pins as a tie
point to mount the resistor and cap. I had to snip the solder lugs
off the new connector so it would fit the old board and put a shim
underneath to insulate the stubs from the board.
     The connections are as follows... luminance is pin 1. Chroma
is taken off the VIC chip at pin 14, that line routed over to the
A/V socket (now an 8 pin) and connected to one of the top unused
pins at the rear of the socket. From that pin, connect a 0.1uF cap
and 330 ohm resistor in series with the final connection to the
middle pin of the socket, pin 6.
     With the above arrangement the socket will still work with a
five pin A/V connection for composite but will now work with an S
monitor such as a 1702, 1902 or 1084. To run the S output to a TV
with an S input jack, you need to make an adapter cable with the
eight pin DIN on one end and a four pin mini-DIN on the other. I
would add two RCA cables to tie the mono-audio to both TV speakers.
     Lastly, although the eight pin socket can be salvaged from an
old dud C64 board, eight pin plugs are hard to get. I use an eight
pin circular DIN plug (the original A/V plug is U shaped) and I
removed the two top unused pins so it would fit the new A/V socket.
Rather than cutting the pins, use a soldering iron to heat them
from the solder side and just pull them out... much easier on your
cutters. ;-)