Years ago when I was repairing tv's either bench or outside, on the counter we had a cartoon cut out of the comics. The first pic was a guy standing at the counter .caption my tv is broke. Next caption can you be more specific? My 19" portable is broke. I took many calls and a common complaint was my on-off switch is broke. How do you know? Well you turn it on nothin happens. It was like pulling teeth sometimes..
Same thing on the forums
I got interference whats wrong. With a pic of the interference I could tell in a minute But 90% of the time if I do get a description of the video display they have given up and gone on to something else. And I have fought every type of intererference man-made or natural in super high freqs (microwave or radar) uhf vhf fm am and audio.
And the same with video distribution or modulator problems. It is not complicated but I will try to give a little tutorial on karaoke video.
Raw video or composite (with sync) consists of the video component which ranges from dark gray to bright gray ( there is no such thing as black or white) This ranges from 0 volts to + .7 volts which is the brightest. On the bottom are the sync pulses with NTSC (60 hz) there are vertical sync pulses which are square waves and synchronizes each frame at a 60 hz rate..There are also over 600 line sync pulses per frame which syncs the sweep in the crt and paints the pic For every line there is a short burst of 3.58 mhz signal that syncs the color oscillator in the monitor and thus provides the correct amount of green red and blue...
S-video sends 2 signals the video and the burst For what reason I dont know.All a s-video to rca or composite converter does is run the color burst back into the video with a nickel 470 pf capacitor..
A video board in a comp has to make up the video (using memory and provide the sync pulses and burst in rca or s-video out. Raw video is normally run thru a 75 ohm shielded cable (long studio runs) but any cable can be used in short applications with a termination resistor which is a 75 ohm resistor to ground in the monitor or rf modulator .. This provides the proper load and develops the max video at that point. The video board sense this load and switches the video to this output In properties if you click extend my desktop and it doesnt stay that means nothing is hooked up or it isnt terminated. In some apps esp win 2k the board has to be terminated when booting up...
Some moitors have either s-video or rca video inputs For multiple monitors a video da (distribution) amp is needed store bought are expensive but a tech can make them for a few dollars. Even in a snake either can be run up to a 100 feet to the stage monitor.
To run to tvs channel 3 or 4 a modulator is needed All it does is modulate the video with a rf frequency If I remember right channel 3 is 56 mhz to 60 mhz. Most modulators will handle 2 tv's although a splitter can be used Samo samo for more a distribution amp is needed iInthis category they are more expensive and at this time require a little bit of engineering.. Db loss per foot number of drops etc... I have also experimented with wireless..
Both methods are subject to rfi or internal power interference and with proper methods can be solved.. I hope this solves some mysteries for some and helps a little down stream...
