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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Help with JVC AV-2779S Verticle Problem
Hi there! I've been reading the posts on verticle problems,
particularly on JVC TVs, and have come up short fixing my TV. One evening recently, the TV suddenly developed vertical foldover at the top. There was no for-warning to this. After reading many posts, I tried first to resolder the vertical chip (TA8432K) and surrounding components. I then replaced the boost cap (100uF 35V 105C)and the pair of 470uF 35V caps in series with the yoke. I've checked the boost diode and 70-ish volt zener (no schematic, so I'm not certain what the voltage rating of the zener is) and neither one is shorted or open. I'm seeing about 12 volts DC on the low voltage vertical supply, and 27 volts DC on the "high" voltage vertical supply (with 1 volt AC ripple on my VOM). The boost cap gets charged to about 26V, but doesn't appear to ever discharge (0 volts AC voltage reading on my VOM). I only have a VOM to troubleshooting (though I'm borrowing an o'scope this weekend to view my waveforms). I also noticed that the verticle pincushion is slightly off--easily seen on letter boxed DVDs. For a scan line above the center of the screen, the left and right sides of the scan are above the center, though only slightly, but enough to give it a very slight bowl shape. So I'm left with several choices (as I see it): the ramp is bad, the vertical IC is bad, or the vertical PS is wobbly (bad filter caps? that's my next check once I get the scope). The ramp is generated by the vertical IC, btw. I swapped out the ramp cap, too, with no change. Any help, insight, or assistance would be GREATLY appreciated. Thanks! Nathan |
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