Composite Sync in CRT Emudriver: is it working for you, and what is your setup?

[CRTFTW]

So what is everybody's setup regarding C-sync? Are you combining it physically in some way, or you using software C-sync? Furthermore, what GPU, and what OS? What sort of problems did you encounter on the way?

I ask because I'm setting up another computer with Emudriver and hitting a snag.

This is with a PVM 1953MD, GPU is r5 430. PC is a Dell with i3 7100 running Windows 11 25H2.

I've had success with Windows 11 in the past, but maybe something has changed in the interim. I understand Win 11 isn't officially supported, to the degree any of this is official.

Anyway, I can bodge composite sync by just using a T-connector and it works, and both H and V sync need to be negative.

I flipped on software composite sync, only left H-sync plugged in, and I got a stable picture for a few seconds that faded to black. Like it getting too much voltage or maybe not enough? Very odd. Perhaps it needs a 470ohm resistor? Though in my understanding, a lot of PVM's are quite tolerant of different sync voltages.

Also, this contrasts with my experience with software C-sync in the past on a 20L2 where I used ++ polarity, and it worked seamlessly.

So yeah, I'd like to simplify things and just use software c-sync, but I'm not sure if/how it's possible.

[Zebidee]

Anyway, I can bodge composite sync by just using a T-connector and it works, and both H and V sync need to be negative.

If this works a looks OK then why not? 

You may get a slight "zigzag" near the top of the screen as the PVM tries to decide where to start the frame.

It is a good idea to run this through a resistor (470R to 1K should do the job) to bring sync levels <1v (0.3vpp "ideal", but <1v should be fine). Otherwise the PVM's sync tip clamping circuit has to cut the excess voltage and siphon it off. It might seem fine for now, but save it the trouble and save yourself repairs in the future.

I have a Sony CRT monitor I'd been running 5v smushy sync into for a long time and now the sync is starting to wander. Silly me. A resistor costs less than one cent.

I flipped on software composite sync, only left H-sync plugged in, and I got a stable picture for a few seconds that faded to black. Like it getting too much voltage or maybe not enough? Very odd. Perhaps it needs a 470ohm resistor? Though in my understanding, a lot of PVM's are quite tolerant of different sync voltages.

This fading to black is weird - sync should just work or not work, maybe rolling picture but not fading. Sync does not carry any actual pciture information - it just tells the display when to start drawing the next lines/frames. Ideally you'd hook up an oscilloscope to see what sync signal you are getting.

I suspect there is something going on in your setup. Are you sure that you enabled composite sync for the correct video head in VMMaker? There is a pull-down list.

Be sure to disconnect the V-sync line when using composite out from CRT_emulator as this does NOT switch off the V-sync signal, and it will interfere destructively.

Use the resistor (refer above).

So yeah, I'd like to simplify things and just use software c-sync, but I'm not sure if/how it's possible.

Buttersoft was selling some tiny dongles that take VGA H+V sync in, and give VGA composite out. They also filter out non-15khz signals. Not sure if he's still doing those, but I have a couple and they are pretty handy.

Finally, you can make your own circuit to create composite sync - it actually isn't that hard, but is maybe a conversation for a different thread on another day.