Lowering voltage on MVS sync line

Yesterday I measured the sync line on my MVS-1C board and found that the vmax was around 5.8V which is very high. The recommended 470ohm resister I had on the line didn't do much to lower this of course, so I added a 100ohm as pulldown to create a voltage divider and got around 1V.

http://www.ohmslawcalculator.com/voltage-divider-calculator
Voltage (source) 5.8V
R1: 470ohms
R2: 100ohms

And this does work well enough. But today I started wondering if the pulldown resistor has too low a value. Could this be a problem? Replacing the resistors with 4.7k and 1k should give the same result, should I do that instead, or is there a better way to lower the sync voltage?

 

Are u connecting your MVS to an arcade monitor or TV. There is already a termination resistor in the monitor or TV so adding another pull down resistor will affect the other restance values afaik. For a 5V ttl voltage, a 470 Ohm series resistor should be enough as there is a 75 Ohm termination resistor in the TV.

 

Yes, when you add the 470 ohm resistor, you must measure the voltage with the TV connected. Without the TV, the 75ohm resistor in the TV (that forms the voltage divider) isn't present and you won't notice a voltage change.

You could add your own 75ohm resistor just for testing purposes, then remove it when you are ready to connect it to the tv.

 

Ah of course, I completely forgot about the 75-ohm termination. I'll remove it again then

The signal chain goes like this:
cMVS > 470ohm > Extron RGBHV Matrix > 470ohm > OSSC.

The reason that I have 470 on the Extron output is that regardless of the input it will output 5v TTL (I believe it's called) on the sync voltage.

I'm actually not sure what the input termination is on the Extron. On one of my units I can set this to 75ohm, but only for a few of the inputs, the other value is 580ohm I think. But my guess is that the Extrons don't mind either way.

 

To my knowledge, Extron boxes can accept either TV level or TTL level sync inputs fine. I know my RGB 201 Rxi is rated for it according to the manual. As for the output, it is TTL level sync like your Matrix. My PVM and LCDs are designed for it so I don't bother with 75 ohm termination on the output.

Thankfully, Extron keeps manuals for their products on their website, even for retired units like my Rxi. You can look up your Matrix on their site and see if it says it in the specs.

 

Yeah it wouldn't make much sense if these things didn't support TTL sync

Unfortunately I don't know the exact models of my units, and disconnecting them to look at the back would take hours

EDIT: What is the proper voltage for regular TV-level? Some sites say 0.7 others say 1V.

 

If I remember correctly, TV requires around 0.7V for the RGB signals and anywhere between 0.3 - 1.0V for the CSYNC signal. Below 0.3V and the ADC may not pick it up, and over 1.0V may stress the ADC. Hence why it is good to step down TTL signals.

 

Thank you