Samsung PS50a410 - Page 3

vinceroger69 · 05-18-2012, 01:29 AM

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

tom66 · 05-18-2012, 03:21 AM

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 · 05-18-2012, 03:22 AM

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 · 05-18-2012, 05:44 PM

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

nickdablack · 05-18-2012, 05:52 PM

http://www.thinking.com.tw/documents/en-sck.pdf
SCK - Brand
20 - 20mm
206 - 206ohm
L - 15% tollerance
S - Straight Lead
Y - RoHS & HF Compliant

nickdablack · 05-18-2012, 06:28 PM

Quote:

Originally Posted by tom66

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 · 05-19-2012, 12:36 AM

Quote:

Originally Posted by vinceroger69

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 · 05-19-2012, 02:10 AM

Quote:

Originally Posted by nickdablack

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 · 05-19-2012, 02:44 AM

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

tom66 · 05-19-2012, 03:11 AM

Where is DB803 on the board?

nickdablack · 05-19-2012, 03:50 PM

Quote:

Originally Posted by tom66

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 · 05-19-2012, 04:14 PM

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 · 05-19-2012, 04:55 PM

Quote:

Originally Posted by tom66

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 · 05-19-2012, 06:08 PM

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 · 05-19-2012, 06:28 PM

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

nickdablack · 05-19-2012, 06:50 PM

Quote:

Originally Posted by tom66

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 · 05-20-2012, 03:20 AM

It says in the datasheet

Maximum Capacitance @ 240 VAC: 2,170 µf

So I think you'll be fine.

nickdablack · 05-20-2012, 07:21 PM

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

nickdablack · 05-22-2012, 12:37 AM

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 · 05-22-2012, 05:08 AM

Quote:

Originally Posted by nickdablack

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.

05-18-2012, 01:29 AM	#41
vinceroger69 Badcaps Veteran Join Date: Mar 2012 City & State: coventry My Country: uk I'm a: Knowledge Seeker Posts: 555	Re: Samsung PS50a410 a thermistor maybe? do those diodes test ok next to it?

05-18-2012, 03:21 AM	#42
tom66 Badcaps Veteran Join Date: Apr 2011 City & State: University of Leeds (MEng ElecEng undergrad) My Country: UK Line Voltage: 230Vac 50Hz I'm a: Student Tech Posts: 13,472	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. __________________ Begin Signature I fix TVs and electronics as a hobby and to save nice things from the dump. 40 LCD TVs, 4 monitors, 13 plasma TVs, and a 6.1 system! Free service manuals database: http://www.tgohome.com/ServiceManuals - Have a manual? Need a manual? Please PM me. I have successfully fixed (from best --> worst build quality): 3 Panasonic Plasmas, 1 Yamaha HTS, 1 NEC Plasma, 2 Sharp LCDs, 2 Toshiba LCDs, 5 Philips Plasma/LCD, 1 Hitachi Plasma, 5 LG LCD/Plasma, 10 Samsung LCD/Plasma, 1 Thomson Plasma, 1 Atec LCD, 1 Hanspree LCD, 1 Xerox LCD, 1 Harwa LCD, 2 Proview LCD, 2 Hyundai LCD, 1 "Onn" LCD, 1 Dell LCD, 1 iiyama LCD, 1 Logik LCD, 5 Bush LCD, 9 Vestel LCDs [Please do not PM me for help: I am a busy student, and we prefer input from all sides on this forum.]

05-18-2012, 03:22 AM	#43
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	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. Last edited by nickdablack; 05-18-2012 at 03:24 AM..

05-18-2012, 05:44 PM	#44
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	Re: Samsung PS50a410 OK so its an NTC. Now to work out the Value. SCK20206LSY

05-18-2012, 05:52 PM	#45
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	Re: Samsung PS50a410 http://www.thinking.com.tw/documents/en-sck.pdf SCK - Brand 20 - 20mm 206 - 206ohm L - 15% tollerance S - Straight Lead Y - RoHS & HF Compliant

05-19-2012, 02:44 AM	#49
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	Re: Samsung PS50a410 OK my new shopping list is: Replace IC - UCC28060 Replace Diode - 1N4007S Replace Thermistor - SCK20206LSY

05-19-2012, 03:11 AM	#50
tom66 Badcaps Veteran Join Date: Apr 2011 City & State: University of Leeds (MEng ElecEng undergrad) My Country: UK Line Voltage: 230Vac 50Hz I'm a: Student Tech Posts: 13,472	Re: Samsung PS50a410 Where is DB803 on the board?

05-19-2012, 04:14 PM	#52
tom66 Badcaps Veteran Join Date: Apr 2011 City & State: University of Leeds (MEng ElecEng undergrad) My Country: UK Line Voltage: 230Vac 50Hz I'm a: Student Tech Posts: 13,472	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? Last edited by tom66; 05-19-2012 at 04:17 PM..

05-19-2012, 06:08 PM	#54
tom66 Badcaps Veteran Join Date: Apr 2011 City & State: University of Leeds (MEng ElecEng undergrad) My Country: UK Line Voltage: 230Vac 50Hz I'm a: Student Tech Posts: 13,472	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.

05-19-2012, 06:28 PM	#55
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	Re: Samsung PS50a410 Sounds good. I'll have to go back to farnels. The other guys dont cary all of those items.

05-20-2012, 03:20 AM	#57
tom66 Badcaps Veteran Join Date: Apr 2011 City & State: University of Leeds (MEng ElecEng undergrad) My Country: UK Line Voltage: 230Vac 50Hz I'm a: Student Tech Posts: 13,472	Re: Samsung PS50a410 It says in the datasheet Maximum Capacitance @ 240 VAC: 2,170 µf So I think you'll be fine.

05-20-2012, 07:21 PM	#58
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	Re: Samsung PS50a410 Thanks again. Parts ordered. Round 2 later this week.

05-22-2012, 12:37 AM	#59
nickdablack Member Join Date: Apr 2012 City & State: Melbourne My Country: Australia Line Voltage: 240vac 50Hz I'm a: Hobbyist Tech Posts: 45	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.

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