GE 9" under counter TV video in and out

If the video fades, resolder the CRT heater pins on the neck board, it's almost certainly something in that circuit.

Sounds like a good suggestion. None of the solder joints appeared to be bad, but I know how that goes. I've resoldered all of the points on the neck board, and the set stayed on longer than it had in the past. I'll know tomorrow for sure.

Thanks. Dan

I spoke too soon. After soldering all of the points, the problem is still there.

Dan

It could be further down the line as well, just trace the heater circuit. You can verify by running the set with the cover off in a dark room and see if the heater glow fades.

You're right on. The heater does fade out at the same time that the problem occurs. I'll try to trace the rest of the heater circuit.

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James is almost always "right on".

Greetings Dan..

Regarding: "There is a NPN transistor labeled TP15 which appears to get hot enough to discolor the board beneath it. This transistor checks OK with an ohmmeter, but may be breaking down under higher voltages."

This may be an issue where the component (transistor) is getting SO hot as to make the solder connections and thus the electrical connections intermittent.

Some of these multi-pin ICs and transistors can get very hot indeed. I've had a similar situation with a vertical oscillator / amplifier IC that resulted in the horizontal line as the IC got hot. I got into the motherboard, sucked up the old solder (Soldapullt). And applied some new heat sink compound and remounted the IC and re-soldered the connection with fresh solder. Clean up the resin afterwards with Alcohol and all has been well for several years.

Likewise, the first thing I would do is unsolder your suspect transistor, pulling up the old solder. IF it's heat sink mounted, make sure you have wiped off the old heat sink compound and apply some new fresh silicon based heat sink compound and re-solder the transistor with fresh solder. Clean up the residue and see if that doesn't resolve the issue. IF your transistor, in this case, is electrically sound, this may be all that is needed. Ultimately, you wan to do what you can to cool down the operation of that transistor, especially if its been discoloring the PC board beneath it.

Cheers, Mr. Mentor

The transistor is fine, it's perfectly normal for cheap phenolic circuit boards to darken. We already determined that the problem is in the power to the CRT heater.

James, I'm sorry that my description of the problem has been inadequate. Yes, the video does fade in and out, but so does the sound. The set seems to be turning itself OFF and ON periodically. So, the problem may be even further back than the heater circuit. I am beginning to suspect something in the remote control circuit.

Mr. Mentor, the transistor which has a discoloration in the board beneath does not have a heat sink, and I have already removed it and resoldered it.

Thanks to all. Dan

Oh, yes that changes things. I would look at the power supply and the pins around the flyback transformer. If the remote circuit was the issue, the power relay would be clicking in and out.

As James says, you've gotta be looking in the power supply. I think that personally, I would feel inclined to just replace that transistor that gets hot, even if it appears to read ok on static ohms testing. If it is one of those large format D-line packages, just replace it with a general purpose flatpak - whatever comes to hand in the right NPN or PNP flavour. Chances are that transistor is either a regulator, or a standby switch, and it may well fail when it gets hot. I have had this with transistors in that sort of position, many times. You could just stick your voltmeter on (probably) the emitter pin (possibly the collector pin) and just see if the voltage goes away when the set goes off. If it does, check the other pin (collector or emitter) and see if the input volts are still there. If they are, and the base volts have not changed significantly, then the transistor is faulty. If that's all too much trouble, buy a can of freezer, and give the transistor a good squirt when the display goes off, and see if that restores it for a while. I also agree with James that the remote circuit is most unlikely to have anything to do with this problem.

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Does it really "fade" out? Or do you really just abruptly lose video?

Given the problem cycles, it really does sound thermal. Given that you lose the audio, too, it sounds like power supply. Does this happen with the cover(s) off? If so, got any freeze spray? If so, run it w/covers off, then when problem occurs, gently spray a few drops of freeze liquid onto suspect components, see if you can make it stop that way.

=2E..or have you already tried this approach?

Thanks to all! You have been a great deal of help. I was away for the day so I couldn't get back to the set until this evening. It did appear to be a problem which was thermal in nature since it played without difficulty for the longest period of time when it was first turned on. I acquired a can of freeze spay tonight from my local Radio Shack and started to try and locate the problem component. Spraying the transistor with the discolored board beneath didn't do a thing, but spraying the HOT cures the problem at least until it heats up again. As soon as I get a replacement, I'll post the results.

Thanks again. Dan

Does it really "fade" out? Or do you really just abruptly lose video?

Given the problem cycles, it really does sound thermal. Given that you lose the audio, too, it sounds like power supply. Does this happen with the cover(s) off? If so, got any freeze spray? If so, run it w/covers off, then when problem occurs, gently spray a few drops of freeze liquid onto suspect components, see if you can make it stop that way.

...or have you already tried this approach?

Try resoldering the existing HOT first, they don't usually fail that way.

Greetings Dan..

Regarding: "| Try resoldering the existing HOT first, they don't usually fail that way."

Funny, I seem to have heard about such recommendations before..

Dan, I've also heard of a similar situation on a larger 19" set that had a resettable fuse issue on the AC input. Ends up it was not working correctly and was intermittent with heat. The symptoms were the set would work for the longest time and just shut off by itself. Usually worked when cold until which time it warmed up. But even that wasn't a sure thing since this anomaly was truly intermittent. Many an individual thought it was the power supply or the HOT shutting down - ends up both were fine. This is merely an FYI..

Cheers, Mr. Mentor

| > Thanks again. | > Dan | | | Try resoldering the existing HOT first, they don't usually fail that way.

James, I know what you mean about not usually failing that way. As I recall, every previous HOT that I have changed failed completely with a short between emitter and collector. In this case, resoldering does not change anything. Maybe this will be in the category of first time for everything.

Thanks again. Dan

Mr. Mentor, In this set, there is simply an old type fuse, but thanks for the input. I've ordered the HOT and am going to change it. I'll let all of you know whether that solved the problem or not.

Dan

Well anything can happen, I just haven't seen this with a HOT, not saying it's not possible. I'm curious to hear the results of changing it out, hopefully that fixes it.

Well, you were correct James, although for a while I thought that the new HOT had corrected the problem. After I installed the new HOT, the set continued to operate for about 1/2 hour. Since it had previously started its cycling of off and on after about 5 minutes, I initially thought that it was fixed. I left the set ON just to be sure and left the room. I came back in about an hour to find the set completely off. The fuse had blown, and the new HOT now has the classic fault of a short between the emitter and collector.

Dan