Samsung LE37B550A5W Dead

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Hi All

I have a Sammy that is dead, I am getting no voltage on the 30pin connector..more importantly no 5v from pin 27, I am getting 330v at smoothing cap, all usual suspects all ok, both internal fuses are ok, fets are ok, solder joints seem fine.

No backlight flash with main disconnected

It wont let me attach pics..maybe because I am a noob (managed to sort it)..if you need me to uplad better pics lt me know

Anyone give us any pointers please

[budm]

Re: Samsung LE37B550A5W Dead

Can you please post good clear pictures of the board? I cannot read the P/N on that power supply board. Is it BN44-XXXXX?
It is hard for us the troubleshoot the board whe we cannot clearly see the components and traces of the boards.

[martyparish]

Re: Samsung LE37B550A5W Dead

I'm pretty sure you can attach pics even if you only have one post. Click the "Go Advanced" button and see if a "Manage attachments" button is there.

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Re: Samsung LE37B550A5W Dead

Sorry crap camera...these might be better, pn bn44-00262a

[tom66]

Re: Samsung LE37B550A5W Dead

Schematic.
http://www.tgohome.com/ServiceManual...&Search=Submit

[budm]

Re: Samsung LE37B550A5W Dead

Here is the bulletin for the BN44-00262A and the diagram from TOM66 web site.
Hi tom, do you want to upload the bulletin to your site?

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Re: Samsung LE37B550A5W Dead

Thanks for the schematic, the diode mentioned in the bulletin this reads ok in and out of board...do I change it anyway...I dont think the problems lies here though..but will change if needed

I think I need to get the 5v back first

Cheers

[budm]

Re: Samsung LE37B550A5W Dead

Yes we need to troubleshoot the 5V section first.
See the diagram I posted.
Check the snubber diode, DP801.
Check the voltage on the two legs of capacitor CM804.
Check the resistance of the IC UM801S (STR-W6252, TV unplugged) between Ground pin5 aginst all other pins.

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Re: Samsung LE37B550A5W Dead

Check the snubber diode, DP801.

DP801..I cant find it, I can see dm801 sat next to cm804

CHeers

[budm]

Re: Samsung LE37B550A5W Dead

It should be close to the 5v stby transformer TM801S, the Cathode of th at DP801 is connected to RM811 and CM805 per diagram.

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Re: Samsung LE37B550A5W Dead

Sorry the only diode I can see by tranny is DP810...will come back to that

CM804 Voltage = 0.0v

Pin 1= No reading
pin2=1.1Mohms
pin3= No reading
pin4=1.1Mohms
Pin6=No reading

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Re: Samsung LE37B550A5W Dead

It should be close to the 5v stby transformer TM801S, the Cathode of th at DP801 is connected to RM811 and CM805 per diagram.

DM801 is connected to Rm811 and cm805 on the board..DM801 reads ok

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Re: Samsung LE37B550A5W Dead

I have just replaced UM801S with a STR-W6253 and now the voltage at CM804 is 130v

Edit still 0v at pin 27

[budm]

Re: Samsung LE37B550A5W Dead

It sounds like you are not using the correct ground ref for the primary (hot) side of the circuit ofr taking the voltage readings on the primary side. The negative leg of the large 450vdc cap is the ground ref point for the primary circuits, do not use chassis as the ground ref point. The chassis is the ground point for the secondary (cold) side of the circuits.
I expect the DC voltage to be around 20vdc, you can measure right at the two legs of the CM804. IF you do have voltage there on CM804, that means the 5V STBY is working.
The 5V (STB_5.2V) STBY is at pin 3 of CNM802 is an always on power supply. The 5.3V (pin 13 ~16) and the 12V (pin 19) are switched on when main board sends the signal (PWR_ON/OFF) to PIN1 (>3VDC ref to chassis ground since this is the cold side of the circuits)) to turn on the 5.3V and the 12V power suuply.

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Re: Samsung LE37B550A5W Dead

Ok thanks

Pin3 = 0v

CM804 = 0.04v

[budm]

Re: Samsung LE37B550A5W Dead

From your post 11:
"Pin 1= No reading
pin2=1.1Mohms
pin3= No reading
pin4=1.1Mohms
Pin6=No reading"

Pin 3 is the Source pin of the power MOSFET inside the UM801S which is connected toground through the Source resistor RM869 (0.3 Ohm). Check the resistance reading of that resistor.

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Re: Samsung LE37B550A5W Dead

I am getting 0.3ohms there

[tom66]

Re: Samsung LE37B550A5W Dead

Something isn't right with your measurement on pin 3 then, or the device isn't soldered to the board properly.

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Re: Samsung LE37B550A5W Dead

I have not got any voltages on any pin on the connector...before and after me changing UM801S.

I dont know if it makes any difference to your train of thought but the cause of the failure was a power surge..the tv wouldnt work after a power cut

[budm]

Re: Samsung LE37B550A5W Dead

Well , that is an important info to know.