Samsung PS50a410

[vinceroger69]

Re: Samsung PS50a410

a thermistor maybe? do those diodes test ok next to it?

[tom66]

Re: Samsung PS50a410

Inrush limiting thermistor. Almost any ~10A capable device will be fine to replace it. It's quite likely that the NTC acted as a fuse there and isn't the cause of the fault - I suspect a controller IC somewhere has been "wounded" and is malfunctioning.

[nickdablack]

Re: Samsung PS50a410

A non linear resistor is the closes symbol match I can find. I have packed up for the evening so I'll do some measurements tomorrow.

Edit: Ok yes I am an idiot, and a thermistor is a non linear resistor.

[nickdablack]

Re: Samsung PS50a410

OK so its an NTC. Now to work out the Value.
SCK20206LSY

[nickdablack]

Re: Samsung PS50a410


SCK - Brand
20 - 20mm
206 - 206ohm
L - 15% tollerance
S - Straight Lead
Y - RoHS & HF Compliant

[nickdablack]

Re: Samsung PS50a410

Inrush limiting thermistor. Almost any ~10A capable device will be fine to replace it. It's quite likely that the NTC acted as a fuse there and isn't the cause of the fault - I suspect a controller IC somewhere has been "wounded" and is malfunctioning.

Ok now to find the malfunctioning IC. Am I going to need an oscilloscope?

[nickdablack]

Re: Samsung PS50a410

a thermistor maybe? do those diodes test ok next to it?

Excellent call. DB803 had split in half. Not too sure how I missed that.

[tom66]

Re: Samsung PS50a410

Ok now to find the malfunctioning IC. Am I going to need an oscilloscope?

I'd say only the IC attached to the PFC FET you replaced needs replacing.

[nickdablack]

Re: Samsung PS50a410

OK my new shopping list is:
Replace IC - UCC28060
Replace Diode - 1N4007S
Replace Thermistor - SCK20206LSY

[tom66]

Re: Samsung PS50a410

Where is DB803 on the board?

[nickdablack]

Re: Samsung PS50a410

Where is DB803 on the board?

Its in the correct area. Looking at the original photo I didn't see it had cracked. Oh well that's an easy fix. Still think I need to replace the IC? (as much as i love surface mount soldering)

[tom66]

Re: Samsung PS50a410

By it's position, I'm guessing it would be better replaced by a UF4007 because it's going to be involved in the switching part and needs to be fast. 1N4007's are really slow parts - fine for rectifying mains but not much more!

I'm not certain about the IC.

When you replaced the fet...
1.) what replacement did you use?
2.) did you re-apply thermal paste?
3.) did the TV display anything sensible?

[nickdablack]

Re: Samsung PS50a410

When you replaced the fet...
1.) what replacement did you use?
2.) did you re-apply thermal paste?
3.) did the TV display anything sensible?

1) I sourced the same fet.
2) The Fet didn't have thermal paste, just thermal pad.
3) The tv displayed static, but I did not have an antenna in. I presume it was on analog input.


I am also struggling to find a suitable replacement thermistor. I'm looking at www.jaycar.com.au (the only shop open today).
Cant find a 10A thermistor. Is a lower amp just going to blow again?

[tom66]

Re: Samsung PS50a410

Ah, okay - hmm. Strange that it would just blow like that.

As a precaution, it may be a good idea to replace the 450V capacitors on the primary as it has been seen that these can kill the PFC fets if they go bad. (Maybe the burn mark did more than damage the label of the cap.)

For the NTC... you might be able to use a 3-5 amp device as this unit would probably pull less from a 240V AC input.

[nickdablack]

Re: Samsung PS50a410

Sounds good. I'll have to go back to farnels. The other guys dont cary all of those items.

[nickdablack]

Re: Samsung PS50a410

For the NTC... you might be able to use a 3-5 amp device as this unit would probably pull less from a 240V AC input.

Hows this?
http://au.element14.com/jsp/search/p...sp?sku=9008187

[tom66]

Re: Samsung PS50a410

It says in the datasheet

Maximum Capacitance @ 240 VAC: 2,170 µf

So I think you'll be fine.

[nickdablack]

Re: Samsung PS50a410

Thanks again. Parts ordered. Round 2 later this week.

[nickdablack]

Re: Samsung PS50a410

Thought I would be thorough before firing it up again. found a short across pins 1 and 3 of DP802. I wish I saw that before I ordered parts. Oh well off shopping I go again.

[tom66]

Re: Samsung PS50a410

Thought I would be thorough before firing it up again. found a short across pins 1 and 3 of DP802. I wish I saw that before I ordered parts. Oh well off shopping I go again.

Where is DP802 on the PSU? Seems like that FET took out a few other things with it.