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#1
05-22-2008, 02:45 PM
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Panasonic CT-27612V has no video.
Yesterday I found a 27" Panasonic CT-27612V television. After letting it dry overnight (was left out in the rain, very little rain got inside the TV). I tried it today, and it turns on but there is no picture.
I can hear the HV scanning, and I can even hear it change when I hit the button for video mode, and when I turn the TV off, I see that familiar bright white line that one would see when the TV goes off, so I assume the CRT is still working. There is no image on the screen until I turn the TV off. I can't even get onscreen menus or channel numbers. 
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#2
05-22-2008, 03:27 PM
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Try turning the G2 control on the flyback up. Some sets will blank the video if it loses vertical sweep. If you see a white line across the screen when turning up the G2 control, you have a vertical sweep failure. Also, look for bad solder connections on the chassis. I've seen that a lot, especially around the larger resistors.
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#4
05-22-2008, 04:15 PM
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Get a schematic, locate the vertical output IC, and change it out. Also change out the associated capacitors....If anything check power supply voltage to the section too.
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#5
05-22-2008, 04:31 PM
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Um. Where would I get a schematic? Where is the vertical circuit, and could I try changing the caps in the vertical circuit first?
I want to change the caps first, because I had a Toshiba that had a similar issue, and replacing two caps solved it. (replacing the IC had been recommended for that as well, but I never did and it still works fine.
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| Audiokarma |
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#7
05-22-2008, 05:29 PM
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No service switch that I can find. That was one of the first things I checked.
I'll look at the board again later tonight, and start resoldering any IC's with heatsinks that I find. I didn't find anything that looked blown or damaged, so that fusable resistor is probably intact. I guess if it wasn't, it'd read open if I tested it with a multimeter. EDIT: Took a look at the board, and the three biggest heatsinks have what appear to be transistors on them. I found a smaller heatsink attached to what i'm fairly sure is an IC. In any case, I found nothing that looks blown or open. A definite idea of where the vertical circuit is would help out ALOT!
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#8
05-22-2008, 06:03 PM
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There is no Sams Photofact listed for that TV. The vertical IC will be on a heatsink and is probably an LA7838. It's likely that bad caps took out the vertical IC which then took out the resistor. The resistor may not actually look burned.
I just fixed a cheap Funai set for a friend who claimed it had little white lines at the top of the screen. After several days, the TV shut down. The vertical IC shorted and activated the overload protection circuit in the power supply. There was also a 47 uF cap bad.
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#9
05-22-2008, 07:00 PM
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Okay, the only two IC's that look remotely like the LA7838 are by the metal can with the coax cable input. Lots of little caps around that area as well. There is a large resistor in that area too. The resistor looks fine and gives a low ohm reading when testing in circuit.
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#10
05-22-2008, 07:33 PM
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I took the resistor out of circuit and tested it and it reads 1.7 ohms. The bands on it are red, black, gold, gold.... if I'm reading that right, that makes it a 2 ohm resistor with a 5% tolerance, so i guess 1.7 ohm's is close enough...
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| Audiokarma |
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#11
05-22-2008, 07:52 PM
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Quote:
If that's the case, you are indeed looking for a LA7838 vertical chip. When you replace it, also change the electrolytic cap off of pin 9 - it'll give you trouble in the future. The value varies by model and make, and if there are two in the pin 9 circuit, change them both. Cheers,
__________________
Brian USN RET 22YRS (Avionics/Cal) CET-Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit!
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#12
05-22-2008, 07:59 PM
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Quote:
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#13
05-22-2008, 09:39 PM
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The Sams is 3891. I don't think I have any that new; but, I'll look tomorrow.
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Linear Mode
