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Samsung PS50Q97HD no power up relay clicking repeatedly (original post 2009 !)

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Barryl:
Had a problem with my 2007 Samsung PS50Q97HD, owned from new :

Walked into the room (TV had been left on as usual, or so I thought), but it was off.  Re-booted it and thought no more of it, but about 20 mins later - click - it turned off !  Turned it back on again and forgot about it for a while, but the next day whilst browsing for new TV's (I suspected a PSU fault), it turned off again, immediately came back on, then off.  Even worse, it started pulsing on and off, blue light flashing.   Turned it off completely and tried again.  The longer it was off, the longer it stayed on when re-booted, but overall the total time it would stay on steadily reduced.  It looked to be a heat-related fault.

Found this brilliant forum yesterday, and enrolled.

Found also, the original 2009 posting about a similar problem, possibly with FET, GX801, but the original enquirer could not find this component ?

Anyway, there are several big FETs on a heatsink, one of them is QX801 and sure enough, when looking through an eyeglass (I use a x10 btw, stuck on with bluetack on 2.5 dioptre glasses !), all three legs had dry joints.  One other FET had one iffy one too, so I re-flowed them.

Plugged the mains plug back in and it re-booted, and stayed on !

So far, it has been working for about 5 hours, has its back panel on, and (~17) screws back in (brave ...), is connected up to the Sky Q and all is well !  I think it's fixed  :72:

Motto 1: Get help with lifting it, it's unbelievably heavy.  i didn't at first, but then the Wife helped out and she's got a bad back already ....
Motto 2: Take note of the little black writing (why not red ?), warning about high voltages present, which of course you should expect anyway, but there are two 450V electrolytics on the PSU board, next to a heatsink which has the aforementioned warning on (is it at a high voltage itself, I didn't check ?), so be careful that they are discharged before grabbing things too much (mine read 0.26V, but it had been off for ages.

One other thing : What a shame that the stand could not be left on when removing the back panel, I realise the assembly is stronger as a result of the 6 screws going through the panel itself into the stand, but then the set could be serviced upright instead ?

Here's hoping it keeps working, as  my research into more modern, albeit 4K panels, came up with lots of comments about poor pictures off axis and poor black levels compared to the plasma.  Here's to another 12 1/2 years, even if it does consume 480 Watts, not 120 !!!

downunder:

That was very observant of you. It's a common problem on that power supply. I used to enlarge the solder pads on those 2 FETs by scraping them to the copper and thus being able to add more solder. In worse case scenarios they would also damage some diodes and resistors on the underside of the board, but I'd say you have indeed solved the problem.         Bruce

Barryl:
Thanks Bruce.

I've just switched it on from a cold start and it's still working, it would have stopped by now in the latter stages of the failure mode, so I too think it is fixed.  it's often left on for at least 6 hours a day, so the total amount over the 12 years is around 25,000 hours.  I don't know what the MTBF is for this, or any other model, but I suspect that although heat killed it, it's better than frequent on-offs.

I still wouldn't have found it without the forum, so I'm very grateful.

Barry.

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