Samsung FPT5084 50" Plasma - Randomly shuts off

[PlasmaRon]

Working on the Samsung and can't really see any bad caps on the main power supply so I'm looking elsewhere for issues. I even pulled out one of the 2200uf 10v caps to test it and it was fine.
When it clicks off, it does the red-light dance and needs to be unplugged from the AC and plugged back in.
Any clues or experience with this model

[Sevenqi]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

Please take a look at the power supply board for the cold solder joints.

[PlasmaRon]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

Yes, I figured that would be the next thing to do. Without a microscope I'm not sure how I would examine all the surface mount components on the back. My plan is to use the heat gun on the boards and see if I can get it to switch off quicker. Currently it takes a couple hours before it shuts itself off.

[tom66]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

The cold joints in question are usually very visible; they are cracks around the MOSFETs soldered to the board and bolted to the heatsink.

[PlasmaRon]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

Looked for cold solder joints but nothing like that on the PS.. I tried the heat gun but nothing definitive at all. I found that if I unplug the Y and Z boards I can still get sound so I'm taking those one at a time to see if the thing powers off with each of those boards unplugged in turn.

[PlasmaRon]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

I found the problem! There's a thermal sensor attached to the end of the heat sink on the main power supply and it was causing the power supply to shut down because the heat sink was too hot. I removed the top of the heat sink and reapplied thermal compound and tightened up the screens holding it in place and now it runs great. I used the heat gun moving slowly around the set 'till I found the spot that was sensitive and then narrowed in on it from there.

[mmartell]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

Nice catch.

[Sony_crack]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

I have the shutdown after start and the alarm on the power board says TH_DET....if I put a fan on the thermistor it'll keep running. Replacing the thermal compound didn't help me, but I believe I have a similar or same problem.

[Sony_crack]

Re: Samsung FPT5084 50" Plasma - Randomly shuts off

Capacitor CQ810 ( 50V 47uF ) had high ESR ~18ohms. Once i replaced the capacitor the power board would click, but no startup. Found no 15V output from UQ802 ( 15V regulator ). Replaced the 15V regulator and the tv is back working. Heat cycled it for 2 days, no more shutdowns.