Adding Composite Input (Capacitor Question)

[TinCanAlley]

Originally Posted by Electronic M

There is no fixed DC polarity to the composite video signal. You either determine polarity based on the injection points DC value with respect to ground. Or you use a non-polarized capacitor for the connection...Which you can make out of 2 polarized lytics of double the desired capacitance connected in anti-series...(Not parallel but rather) Series with one cap reverse polarity from how you'd connect 2 batteries in series.

So if I put two 100uf caps negative to negative I would get a 50uf non-polarized cap, right?

[ARC Tech-109]

Originally Posted by TinCanAlley

So if I put two 100uf caps negative to negative I would get a 50uf non-polarized cap, right?

No. One cap going "reverse" is essentially a short to the the waveform so it's going to be about 100uf as the other is running in the "correct" polarity. I'd start off with a pair of 22uf 16V caps back-to-back and work up from there. Remember sync is negative going with respect to ground and visual is positive going so the capacitors should be equal value however playing with the values be it negative or positive going may help work out some balance issues.

Now my question is where are you feeding the composite signal into and is this a televison receiver or real monitor? Reason I ask is twofold. One is the possibility of a hot (AC) chassis with respect to ground and two some TV receivers don't like anything other than what comes from the video detector as I'm fighting this issue now with a Magnavox T940

[TinCanAlley]

Originally Posted by ARC Tech-109

No. One cap going "reverse" is essentially a short to the the waveform so it's going to be about 100uf as the other is running in the "correct" polarity. I'd start off with a pair of 22uf 16V caps back-to-back and work up from there. Remember sync is negative going with respect to ground and visual is positive going so the capacitors should be equal value however playing with the values be it negative or positive going may help work out some balance issues.

Now my question is where are you feeding the composite signal into and is this a televison receiver or real monitor? Reason I ask is twofold. One is the possibility of a hot (AC) chassis with respect to ground and two some TV receivers don't like anything other than what comes from the video detector as I'm fighting this issue now with a Magnavox T940

Isn't two caps connected negative to negative what is meant by "back to back"?

This is a television, but not a hot chassis. It has a full transformer. I'm feeding it into C1 test point which is after the detector stage and where it splits off to the video amp, chroma module, horizontal module and vertical module. This test point is where you attach a scope to see the video signal from the IF.