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#16
04-30-2008, 08:05 PM
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Input is on pin 7. Pin 2 is however part of the video detector circuit. Sounds like you may need to replace that IC. If you inject video at pin 4 and get video, but no video when using pin 7 the IC is bad. You could just look with the scope though. The output from a vcr may be to high for a proper picture.
Bill R. 
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#17
04-30-2008, 09:10 PM
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Quote:
first i want to sincerely thank you for your time, i hope you know how much help your providing. Secondly tomorrow i will try pin 7 (ill scope it). as it sits now i have nothing out of that IC on pin 4. will i have a video signal at pin 2? or am i just looking for any signal? Ill be the first to admit using the vcr was crude but i figured what the heck, and it gave me hope that I can actually fix this (thats what really amazes me). Coming from a mechanic's point of view you guys are geniuses!
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#18
04-30-2008, 11:03 PM
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You will see some form of video on pin 2, as well as pin 3. Pin 7 is the input, 1 is the output to the sound circuits, and pin 4 is the output to the video circuits. Keep in mind that the signal on pin 7 is before the audio take off and before the video detector stage, so the waveform will be an IF waveform, but it will be there. Since you said you have audio, you should have signal at pin 7. Pin 2 and 3 are the 45.75 mhz tuned circuit for the video detector stage of the IC. Be sure to touch carefully touch up the solder connections to the IC, as they can cause problems. Using a vcr is not that crude, but the output from the vcr is composite video so injecting at pin 7 probably will not work. You could use it to check after the IC as you have done. There would be an impedence mismatch, but with a pad to attenuate the signal and a coupling capacitor to isolate it from the DC in the set it could work. I wouldn't expect a perfect picture, but any picture would indicate that the video path was working from that point. The Sylvania part number for the IC is 13-39060-1. It will probably cross to an NTE/ECG replacement.
Bill R
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#19
05-01-2008, 05:44 PM
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k, i checked at pin 7 and had something (my scope is only a 30mhz so it was out of range) but by playing something through the tv i was able to change the signal on pin 7 (amplitude wise was higher verses static on TV). i checked for sound out at pin 1...didnt really see anything (thow im sure its there as the sound works). pin 2 and 3 the same, nothing, but if it was 47mhz at may have been to low of a signal and too out of range for my scope. and for one more check i injected video in pin 4 and got a very out of sync but mostly correct (color wise) picture. injecting it at pin 2 or 3 yeilded a more correct picture that was badly smeared and washed out (but readable and in sync). so thats where im at. does it seem like that IC is dead? If so where may I find another one?
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#22
05-01-2008, 08:27 PM
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By the way any scope over 10mhz is fine for tv work. The bandwidth is only about 6mhz. The tuned circuit is at 45.75mhz, but only a few megahertz wide. So your scope is fine. Hope the IC solves the problem. At the shop that repair would cost about $70.00 around here, maybe $100.00 if they have to pick it up. It is a shame how many of those sets were scrapped because of a problem like that, in favor of a new set.
Bill R
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#23
05-01-2008, 09:15 PM
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Agreed. Hope it works out for you. I'd love to see a picture of the set as well... I never find Sylvanias 'round here
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#24
05-01-2008, 09:17 PM
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Quote:
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#25
05-07-2008, 09:18 PM
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update, my parts are on their way finally. got an e-mail this afternoon saying the check cleared (had to pay with personal check cause i didnt have a business account with them.) so my parts will be here most likely saturday or monday. in the mean time i figured id show you my temporary daily watcher (which also has an amazing picture, this is an amazing set), a Zenith f1336c3 tube hybrid. As usual the pictures cannot do it justice.
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#26
05-09-2008, 09:34 PM
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First I want to thank everyone who helped me on this set....Bill R you were very patient and very helpfull, all of you were a great source of knowledge....i think you can see where im going with this....as Bill correctly led me to diagnose...the low level video detector IC was bad. Replacing the IC brought back a full color picture....heres the details:
today in the mail came a box from prelco electronics, i gleefully opened it like a kid on christmass and found 1 IC-my low level video detector. i was happy to see it looked the same (you never know these days with internet electronics supply places). i removed the offending IC from the TV and popped in the new one. threw the cord on and figured id see what i get before i put the cord back into the back of the set and clip it in place and put the shields back on and whatnot inscase it didnt work. i turned on the power and waited....and waited....and finally....dimly....i got SNOW!! I immediatly shut the TV off and put it togeather fully, and buttoned it up, hooked it to the VCR and tried to get a picture for the first time in over 2 weeks. I had dim picture. twiddling the contrast and brightness controlls helped but the picture kept cutting out....i found the brightness controll was causing this so off with the back again (im getting good at this) and found that when i slid the back on i must have hit the brightness knob and cracked one of the solder joints....no worries ill solder it....well not tonite since my only soldering gun is at work (booo). So i couldnt get a picture of it in action BUT it IS in action...or will be fully tomorrow afternoon....when i held the brightness knob i got a perfect (same as always on this set) picture!!!! I really cant believe i fixed it....im so happy!!!! it cost me 8 bux after shipping. Below is a picture of the blown video detector IC. tomorrow ill post pix of the set doing its thing again once i reflow the solder on that brightness pot.
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#29
05-10-2008, 09:42 PM
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Resoldered the brightness pot, as promised here are the pix. usual disclamers apply (camraphone, looks flwaless in person). one pic look like the blue convergance is off but its not .
Thanks a million again to everyone. This wouldnt be possable without the help you offered.
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#30
05-10-2008, 11:05 PM
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Glad you saved it! Now it should last until its CRT won't emit any more electrons (roughly 30-40 years lol)
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