Car Video RGB+Csync help!

AVNoob135

Hey guys new to the forum and am in serious help. I mainly install car audio but video seems to be a beast on its own. So I’m hooking up a signal interruptor to my Navi screen so that I can mirror my iPhone apps. My Acura uses RGB Composite Sync
The device in the pic takes the video signal from the navigation head unit and interrupts the signal when switched on. Now, I’ve been able to identify the RGB and ground signals but for the life of me can’t find the C-sync wire. Also oddly enough when I connect my multimeter (negative lead on ground) and (positive lead on and of the RGB video-out signal wires) I get a voltage of about 3vdc. When switched to measure ohms I get a zero reading. I was under the assumption that I should get a reading of about 75ohms??

outoftheknow

Just to point out this a UK forum and what you are doing is likely illegal there. Well using the apps etc (assuming they aren’t controlled like in Caray or Android Auto) certainly is.

Also there is a seperate forum for car AV etc - maybe amid can move your post for you. I’m sure people can give hypothetical advice

noiseboy72

The video output will have to drive a 75 Ohm load, so will have an output impedance of much less than that. A typical auto volt meter will not be able to correctly read the video signal, you will need video test gear for that.

You can use an oscilloscope to monitor the various wires and identify the sync line. Can you program the interrupter for composite syncs or is it limited to H/V syncs only?

AVNoob135

Haha I live in the states. It is completely legal here because the unit has CarLinkit installed which is like Apple CarPlay. Mirrors GPS apps and plays music.

AVNoob135

Thanks for the info. My previous unit came with RGB Comp SYNC . So from my knowledge I am supposed to get a 75ohm reading if I apply one lead to ground and the other to one of the wires coming out. I get a reading of zero! Also I have about 4 wires which I've identified to be as video signals. I was messing around and decided to test it on my TV. I tried each of the cables on both Component and CVBS and was able to get a clear image but it was in black and white (no color). One of the wires didn't produce any image just an all white screen.

noiseboy72

Why would you expect to get a 75 Ohm reading from the output? If you measure the output from a power amplifier, it won't be 4 or 8 Ohms, but most likely as close to zero Ohms as makes no difference. With a typical multi-meter all you are looking at is the DC resistance of the output stage. To work out the output impedance, you would commonly do a load test. For this, you apply a known open circuit voltage, then apply a known load and measure the volt drop. A little bit of maths and the output impedance is measured. On a typical video output, the output impedance is no  more than 1-2 Ohms, so the resistance is likely to be similar. Your multi-meter is not lying to you and is showing you a fair estimate.

It sounds like the image is being sent RGB with composite syncs if you get a clear image with the sync disconnected. Connect all 3 video wire to the component input, set it to RGB and see if you can get a colour image. If the colours are wrong, swap things around until you get colour.

AVNoob135

Thanks for the info and makes total sense. Just tried it and I got color and a clear image going. Only problem is that I can't find the composite sync wire. The image is sliding sideways :/

noiseboy72

Separate H & V Syncs from the sound of it then. 5 wires in total.