Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

[devheart]

Hi everybody. I recently acquired this 2013 Samsung Plasma TV, model PN51F5500AFXZA for free because it wasn't working. The red LED just continuously blinks when plugged in.

The thermistors on the power board look cooked, with some discolouration of the PCB around them. I've attached an image of the board. The thermistors show as shorted when connectivity tested with multimeter.

I tested all the diodes I could see, they all appear working, no shorts. No bulged caps. Nothing else looks shorted or burnt out. The fuse looks fine and tests shorted with continuity.

Power board is: P51FF_DSM PSPF361503A

Should I try replacing the thermistors? I found this part number for thermistor for this model: 1404-001224

[petehall347]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

thermistors do run warm . they should lower resistance as they get warmer ..look up the spec sheets .. they probably start about 2.5 ohms at room temp.

[devheart]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

With the back off, I can hear a click and a high-pitch tone coming from the power board, when the LED blinks. It appears it's trying to boot itself up to some point, maybe a self check, when power is applied, but there's some issue.

Anybody have an idea on whether it's a power supply board or main logic board issue?

Thanks!

[petehall347]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

try unplugging the main board and see if back lights come on .

[ReeceyBurger123]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

I wouldn't advise you run it, thermistor normally blows if there is shorted fets.

[devheart]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

Tried plugging it in without main board. No backlights came on and no click from the power board.

[dick_barton]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

Service manual which may be of help.

Thermistor details
Manufacturer Samsung
Part Number 1404-001224
Description THERMISTOR-NTC;10K ohm

[budm]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

10K Ohms, that can't be right for the Inrush current limiter NTC, they are usually around 3~5 Ohms range..

[petehall347]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

is the inrush thermistor the black one next to power socket ?

[dick_barton]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

It's the two green devices at the bottom of the picture in post #1

[petehall347]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

whoops yes .. black one is varistor ..i just found a schem but only shows one thermistor at 5ohms nt811s .. mustn't be correct schematic ..

[Nick's Tvs]

Re: Samsung PN51F5500AFXZA issue - Power board thermistors cooked?

That power supply is most likely fine. It rarely goes out. With power disconnected and voltages at 0v check the resistance between VS and ground. You may find it to be shorted due to a bad X or Y sustain. If not check the transistors on those boards for shorts to ground.
Also pictures of the back of the set would help.