Can anyone walk me through builidng a sync combiner?

Dr. Willy

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Can anyone walk me through builidng a sync combiner?

I need to turn my negative H & V sync into negative composite sync. Ive searched around the net but cant seem to find a how to, i find a lot of dead links. Anyone have a walk through of parts i would need? I understand this is a pretty basic circuit for someone who does this all the time, but i am still new to doing this type of circuit building so the more basic terms the better.
 
http://www.mikesarcade.com/wiretap/info/SyncInv.pdf

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im not sure how i missed that in my searches. Has anyone built this one? does it work well? anyone happen to have a pic of it built?
 
That's more complicated than necessary... he doesn't need inversion. Just need an AND gate to combine.
What game is this for? If it's a Williams then there is a much simpler solution.

its for a q-bert. i changed the 7407 on the board to a 7406 already to change the sync from positive to negitive, however my monitor doesnt like the two negitive sync signals, it seems to like composite sync, so now i need to combine them.
 
Correct. Sometimes you can get away with just tying those signals together, so you might want to try that first.
Are you hooking up to a particular monitor, or just making a JAMMA adapter?
 
Correct. Sometimes you can get away with just tying those signals together, so you might want to try that first.
Are you hooking up to a particular monitor, or just making a JAMMA adapter?

Mine is kind of a mixed ball of wax. I have a wells d9100, but that only supports vga, so i have the negative sync signal from q-bert going to a gonbes 8200, then out via vga to the d9100. If i just tie the syncs together, i do get a pic on the monitor, but the monitor isnt super happy with it and it loses sync about every 3-5 seconds then comes back about 15-20 sec later and then loses again. However i have tested the setup (gonbes with composite sync hooked up out via vga to 9100) with my jamma test bench and it works great. So my thought is that the gonbes doesnt like the separate sync.
 
Odd that it does sync for a few seconds. I've read that the 8200 doesn't like sync signals that are too high, just for kicks, try adding an 820 ohm resistor in series on the sync line.
 
Odd that it does sync for a few seconds. I've read that the 8200 doesn't like sync signals that are too high, just for kicks, try adding an 820 ohm resistor in series on the sync line.

i will totally give this a shot tonight and see what it does thanks for the advice.
 
You should check out the LM1881... it's used a lot as a "sync cleaner". You can DIY, or they're are available to simply purchase (pretty cheaply).

DogP
 
Sorry for necroposting, however...

I am currently trying to solve this exact same problem. I have a standard VGA H+V sync output which I am attempting to convert to an RGBS composite sync.

I.e. I'm trying to get my JAMMA board sync output to look like it would if I probed an authentic JAMMA board from 1988.

There seem however to be a myriad different ways to do it, and they all seem to produce slightly different results.

I've seen H+V simply OR'd together, I've seen them XOR'd together, I've seen multiple ORs with help from transistors, and now in this thread I've seen them AND'd together, and I've seen diodes and inverting buffers with people saying bother "over-complicated" and "won't work for X".

So, is there a final answer to this question?

Thank you!
 
I've used this design over the years which
works well for me:

SYNCCOMB.gif
 
I've used this design over the years which
works well for me:

SYNCCOMB.gif

Great, thank you!

My only other concern when it comes to multi-gate approaches for sync signals is propagation delay skew. I assume you haven't noticed any though.
 
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I use a 74HCT86 in the circuit for added speed. I haven't
noticed any issues.

JD
 
I use a 74HCT86 in the circuit for added speed. I haven't
noticed any issues.

JD

Perfect, thanks! I assume the H/VSYNC voltages in your schematic are 5V TTL based on the last XOR gate's input. I'm driving them instead via 3.3V CMOS signals, which is still within specs and doesn't affect the RC time constant of the two RC XOR inputs (only a small difference in energy dissipation).
 
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