Intermittent Problems....

[tom66]

What to do when the problem is intermittent?

I got an LCD TV in from someone - an Acoustic Solutions 32"

Fault description - works for a few minutes then dies, sometimes it will die in 30 seconds other times in 5 minutes.

True to their word, it did exactly that after 3 minutes... just switched itself into standby.

So I open it up and powered it up without the case... it ran an hour, not a problem.

Put the case back on - problem cured itself...!! Works for hours...

I don't want to return this or sell it saying it is fixed when it might die 5 minutes later... so what can I do?

It has no bulged caps although it is full of cheap caps. (Aishu, Samxon, Chong, G-Luxon feature, among others.)

[PlainBill]

Re: Intermittent Problems....

The worst of all possible faults -an intermittent, possibly a bad solder joint.

PlainBill

[digge]

Re: Intermittent Problems....

I agree it might be a cold solder joint.

My other guess would be that its caps that are about to fail. When caps are semi failed they tend to vary some in value depending on heat. If you have an ESR meter, measure what you can in circuit and see if you can spot any possible suspects. Also if you have a thermal cam you could use that and spot if any voltage regulator gets hotter then normal (due to bad caps). If you dont have a thermal cam just using your hand might work, just be careful (both from heat and high voltage).

[alexanna]

Re: Intermittent Problems....

What to do when the problem is intermittent?

.

True to their word, it did exactly that after 3 minutes... just switched itself into standby.

Switching itself into standby is interesting.
Have you thought about the possibility of what I'll call marginable voltage? Possibly from one of the voltage regulators on the logic or signal board. You may have a voltage that's just hovering above the 1% threshold.

[tom66]

Re: Intermittent Problems....

Switching itself into standby is interesting.
Have you thought about the possibility of what I’ll call marginable voltage? Possibly from one of the voltage regulators on the logic or signal board. You may have a voltage that’s just hovering above the 1% threshold.

I had my meter hooked up on most of the outputs for a few hours. I saw variations of at most 10mV sometimes during loud sounds and depending on what video input was selected. All rails were at nominal voltage, 5V @ 4.965V and 24V @ 24.43V. I didn't test any other rails, but the 5V(logic) and 24V(inverter) are the most important. 12V is only used by the digital and analog TV sections I believe, and maybe the audio. In my experience LDOs tend to fail abruptly, either they work or they don't. Extensive short circuit/over-current and thermal protections are built in.

Switching into standby - another Vestel chassis I have here does the same thing, so I expect it's a common thing if the rails go out of spec, I've seen it on LCD monitors too.

[tom66]

Re: Intermittent Problems....

Well, it's run for almost all night now... not a problem in sight... Driving me crazy!

[tom66]

Re: Intermittent Problems....

Put the case on properly. Everything screwed together. Still going strong - going to leave it running for all night then think about what to do with it.

[tom66]

Re: Intermittent Problems....

Well, it survived all night with no problem.

[Village Electronics]

Re: Intermittent Problems....

What to do when the problem is intermittent?

I got an LCD TV in from someone - an Acoustic Solutions 32"

Fault description - works for a few minutes then dies, sometimes it will die in 30 seconds other times in 5 minutes.

True to their word, it did exactly that after 3 minutes... just switched itself into standby.

So I open it up and powered it up without the case... it ran an hour, not a problem.

Put the case back on - problem cured itself...!! Works for hours...

I don't want to return this or sell it saying it is fixed when it might die 5 minutes later... so what can I do?

It has no bulged caps although it is full of cheap caps. (Aishu, Samxon, Chong, G-Luxon feature, among others.)

I suspect a heat related problem. You posted no pictures so that is as far as I can go.

Take the back off. Use a hair dryer and see if you can make it fail while trying to isolate and localize. The opposite technique is freeze spray.

I never have heard of that brand but my guess is that it comes in many flavors. It may be a common chassis. Post a picture of the innards.

[cadillacman]

Re: Intermittent Problems....

I vote a bad solder joint. start by checking the power supply.
Check solder at all transformers, header pins or connectors, large resistors/diodes, and heatsink mounted components. also post some pics of the boards in this set. MAbye the ps is used in other sets.

You may be able to get it to act up by wiggling connectors, tapping stuff(with a non conductive tool) etc.. that may halp you isolate the problem area.