The 560OHM resistor seems to do the trick in terms of getting things
looking good on the screen with the SYNC and green going in via a Y
adapter.

However, it would seem the graphics card into which it is being plugged
is somewhat `intelligent' with respect to monitors.  When I picked it up,
I had a choice between 3 monitors: 2 of which would do 1152x900 and one
which would only do 1024x768 (OpenWindows, xwininfo).  I'm testing this
plugged into a Sparc4 with the TCX graphics chips.  Now, when I turn it
on with a GDM-17E20 plugged in, it'll come up in such a way that is
capable of 1152x900 AND I can swap monitors (to the GDM-1960) with no
loss (except for whils things are all unplugged).  What's annoying is if
the GDM-1960 is plugged in when the system boots up, it does not appear
to work out what sync rate it should set for the monitor.

Some digging on SunSolve found the `proper' syntax for setting the EEPROM
on suns:

setenv output-device=screen:r1280x1024x76m

(although the few settings that I tried (x1152x900x{76,66,72}m) didn't
appear to help the above problem.

Sun's InfoDoc 13584 has some information about TCX, in case anyone is
interested.

Darren