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TV/VCR/Stereo Troubleshooting/Television randomly shuts off and comes back on


QUESTION: We have a 46 inch Class Full HD 1080p Toshiba television (Model 46G310U) purchased in August 2011.  It worked great until about 3 months ago.  Then it started randomly turning off and coming back on within 1 minute.  We purchased an in-home extended warranty and have had a service repairman out twice.  The first time, he changed the Reza Link from on to off.  The second time, he replaced the motherboard.  It did not fix the problem.  We have tried to pinpoint when it happens.  The problem does not appear to happen until the TV has been on for a couple of hours at least; in other words, a cold TV does not have this problem.  We also noticed that when our a/c comes on, the TV will shut off, but not all the time.  If we try to replicate this, we cannot.  However, when the TV is cold, the a/c coming on does not trigger the shut off, only when the TV has been running for a couple of hours or more.  Also, the TV will randomly shut off when nothing else is running at all.  It will shut itself off and it will come back on within a minute.
We cannot understand what is happening.  Could it be some component in our TV that is getting overheated and, if so, what could that be?  Any help or suggestions you can give would be very much appreciated as this is making our viewing enjoyment not very enjoyable.  Thanks.

ANSWER: Thanks for the really good explanation of the symptoms.  That helps alot.

My first suspicion is the power supply getting heated OR a bad electrolytic cap in the filter section - your tech would understand what that means.  It may need a new cap or a new PS board.

Here is my assignment for you.   If you can do this it will help determine if my guess is correct.  Pull the set further away from the wall; if wall mounted, see if you can bring it off and away from the wall.  This will help keep the back of the set cooler - where the power supply is located.  Also, if you can, put a small fan behind the set and let it run cooler air to the rear side of the set.  If that prevents the OFF/ON cycle then I think we have the culprit identified.

Let me know how it goes.

---------- FOLLOW-UP ----------

QUESTION: REPLY:  Thank you for your fast answer.  the TV is quite a ways away from the wall.  We will try the fan and see if that works and will let you know.  Again, thanks for your answer.

Another thought is to put a bowl of ice between the fan and the set.  It will help verify you have a heating problem but it will not tell us what part is failing, will it?  But, I can say that electrolytic capacitors in power supplies are famous for acting up as they are one of the least reliable parts in the world of electronics.  The electrolyte used in them is temperature sensitive and the manufacturing process used for them is often questionable.

Fortunately, if you can identify the bad cap they are cheap to replace but sometimes not easy to rip out and solder in its replacement!  

TV/VCR/Stereo Troubleshooting

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