What are safe levels for composite sync with an RGB modded consumer CRT? I have a MiSTer for using with my modded TVs, and was curious about its sync voltage. I don't have an oscilloscope so I made a very, very crude one using an Arduino's analog input and the IDE's Serial Plotter. I connected the analog pin to ground with a 75 ohm resistor to duplicate the connection on the TV. The csync signal from the VGA port was about 1.26V. Then I tested a PC with an ATI card flashed with ATOM-15 for 15kHz composite sync. It was 2.89V. I put a 330ohm resistor in series on the sync line to pull it down since I thought was high.
What are the concerns here? Am I fretting over nothing?
What are safe sync levels?
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nmalinoski
- Posts: 1974
- Joined: Wed Jul 19, 2017 1:52 pm
Re: What are safe sync levels?
Consumer TVs that take RGBS via SCART are designed to take composite video as sync, and therefore expect sync to be video-level, specifically 1Vp-p, -0.3V to +0.7V.
When you're talking RGBS with pro AV gear (and, I think, generally anything that outputs with a DE-15/VGA port), you're talking about TTL sync, which I believe is 5Vp-p (I'm not sure what the specific range is, if it even matters here).
The few consoles that output clean composite sync natively seem to output a voltage somewhere in between, but it's higher than video-level, and I think it should therefore be considered TTL.
If the MiSTer is outputting analogue video over a DE-15, I think it should be expected to be TTL, but that voltage seems pretty low. It's still higher than video-level, and I think will still cause damage over time, but I'd expect it to cause damage slower than higher sync voltages. Still, I think the ideal would be to bring down the voltage to the appropriate range.
When you're talking RGBS with pro AV gear (and, I think, generally anything that outputs with a DE-15/VGA port), you're talking about TTL sync, which I believe is 5Vp-p (I'm not sure what the specific range is, if it even matters here).
The few consoles that output clean composite sync natively seem to output a voltage somewhere in between, but it's higher than video-level, and I think it should therefore be considered TTL.
If the MiSTer is outputting analogue video over a DE-15, I think it should be expected to be TTL, but that voltage seems pretty low. It's still higher than video-level, and I think will still cause damage over time, but I'd expect it to cause damage slower than higher sync voltages. Still, I think the ideal would be to bring down the voltage to the appropriate range.
Re: What are safe sync levels?
I tried the MiSTer with the 330ohm resistor on the sync line and it still worked just fine, so I'll just use it from now on to be safe.nmalinoski wrote: If the MiSTer is outputting analogue video over a DE-15, I think it should be expected to be TTL, but that voltage seems pretty low. It's still higher than video-level, and I think will still cause damage over time, but I'd expect it to cause damage slower than higher sync voltages. Still, I think the ideal would be to bring down the voltage to the appropriate range.