The Logic of Logic Gates

Started by benzaldehyde, January 19, 2004, 09:50:59 AM

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Hi all,

    This is only remotely on topic, but I was having some trouble with a monitor. It would accept C sync, but often wouldn't sync properly. So, I resolved to separate H sync from C and V sync coming off an LM1881. I found a schematic that suggested running the C and V sync through a NAND gate, and then running that output and the C sync through an AND gate. Sounds about right; the NAND gate will filter what is shared, allowing a rough H sync through, and then the AND gate will buffer with the H sync part of the C sync signal. (This is only a rudimentary understanding.  :blink:  ) This, though, didn't work too well for my monitor. I wouldn't get any picture at all. Then ,whist experimenting, I found that replacing the NAND gate with another AND gate actually generated a H sync signal that my monitor perfers rather well. My question is how? I thought the AND gate would only allow that information that both inputs share through. Wouldn't that mean all I'm generating is V sync? Well, in any case, I'll look it up as soon as I can find my electronics book, though that could take months! If anyone wishes to share his or her knowledge, I'd be much appreciative. Thanks!


I had the same problem just now when trying to sync my CDX to my projector.  I found that if I attenuated the CSync a little by putting a 325 or 175 ohm resistor in series, it fixed the problems.  Too little or too much resistance caused the picture to be shaky.  On another monitor, it was hard to get it to sync without the resistor, but once it was synced, it stayed locked on perfectly.  But, with the resistor, all problems seem to be solved.