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Samsung PSPF531801A power board gradually decreasing Va    
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Joined: 30 Sep 2016
Posts: 1

PostPosted: Fri Sep 30, 2016 11:21 am    Post subject: Samsung PSPF531801A power board gradually decreasing Va Reply with quote

Hi everybody,
My Samsung PSPF531801A power board is acting up: the TV starts & functions well but shuts down after 30 to 60secs (TV model HP-5054). This is happening even with all the boards disconnected from the power board.

There were 2 capacitors (1000microF, 25v) that were bulging and that I have replaced, however the same behavior continued.
StBy is at 5V and the "5.3V" pins are at 5.3V with PS-On at 4.0V.
Va is at 61.9V and Vg is at 14.1V.
QS801 and QS802 donít show any sign of problem and have an identical resistance between S and G (when still on the board).

I then replaced 2 capacitors (470microF, 35v) that looked fine.
StBy is at 5V and the "5.3V" pins are at 5.3V with PS-On at 4.0V.
Va is now at 62.4V and Vg is at 14.9V.
The TV shuts off at about 120secs.
Va is constant for about 60 to 90 secs and then gradually decreases until the TV shuts off.

What could lead to the gradual decrease of Va? Should I keep replacing all the capacitors or is there a section of the board I should focus on? There are three large capacitors on the board, but these are not included in the pre-packaged "repair kit" on Amazon for this TV / power board.
Would you have any pointers for my next steps please?

Thanks in advance.

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Joined: 17 Sep 2007
Posts: 36
Location: Chicago, Il, USA

PostPosted: Wed Oct 05, 2016 1:52 am    Post subject: Reply with quote

I'm no expert, but I don't think capacitors would generally cause such an issue. First thing I would do is to check how much time the TV remains on. If the time is the exact same several times in a row, then most likely it's shutting itself off after a programmed amount of time to wait for something to happen (that it doesn't sense). In that case, you'd need to find out what that something is.

If the time span is random, and especially if the time shrinks the more times you do it, I would check for loose plug connections throughout, and look over all the boards for broken solder joints. In my experience, it's quite typical for a broken solder joint to make good, workable contact until the board it's on warms up, either the expansion of the board or expansion of the joint itself will open the connection. Suspect areas are at every soldered-on plug connector and where every bigger-than-normal component is soldered. But still, give everything a looking over under a magnifying glass. Also be sure to look at everything from many different angles. I can't tell you how many times I've missed a crack because of the way the solder reflects light.

And while you're soldering, remember that flux is your friend.
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