Double whamy on my JVC TV

Old 07-04-01, 08:34 PM
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I have a JVC-2774S that's about 8 years old. As soon as I moved from Florida to Mass, it started acting up. First was the tuning inconsistency. I was able to tune to the cable channels between 7 to 49 until the TV warmed up. Recently, this behaviour became very random. I started using my VCR for tuning.

Then, my picture started going bad. I starts out as small horizontal band at the bottom which jiggles up and down. This kept on for a while until the whole picture got squished into a 5 inch horizontal band in the middle. I took the backside off for a look-see. Nothing obvious stuck out (i.e. burned resistor or caps). One thing I noticed while probing was that when I push or pull on a metal heat sink (big power transistor is mounted on it vertically) sticking straight up from the board, the annoying horizontal band goes away. The circuit board is located at the bottom of the set directly below the tube. The heat sink in question is pretty close to the back of the tube. The problem persisted after I put the back cover back on. Tapping the bottom or tipping the TV restores the picture.

If I can fix the picture problem, I can manage with tuning with the VCR. Do you think the picture problem is a relatively cheap fix? Or should I start shopping for a new TV?
Old 07-05-01, 06:02 AM
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Good Morning, LMDS:

Sounds like you have solved your own problems. The problem in both cases should turn out to be bad solder connections within the set.

Solder connections are made by machine manufacture and once in a while a component is not soldered correctly to the circuit board. Running the set and the heat generated within the set will cause these connections to deteriorate and ultimately fail. In your case, you moved the set and added a little physical motion to the equation.

You've solved the problem with the tuner and rather than send you into that territory, you are better off using the tuner in your VCR. I prefer to leave actual tuner repairs to the professionals because of the problems involved.

As for the circuit board, the heat sink you are flexing is most likely on the vertical driver transistor from the condition you describe. In this case, you have the area located on the board. Therefore, you need a low heat (not a soldering gun) pencil soldering iron, a little 60-40 electronic solder, and a little patience.
Access the bottom of the board and expose the affected area.
Use a little solder on the tip of the pencil iron and resolder everything in the area you have located. The solder wells on the circuit board are very pronounced and easy to identify. Usually just a touch with the iron will melt the solder and allow the solder to remake its connection. If you add any solder to a connection, use it sparingly. Solder blobs cause short circuits.

Check the set for normal operation before you put on the back, of course. Since you are searching for a needle in a haystack, sometimes you have to repeat this operation a couple of times until you actually find the offending bad connection.


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