SAMSUNG LA40A450C1XXP Power Supply Problem

[renzy101]

Good day,

Can somebody please help me with my SAMSUNG 40" LCD TV power supply issue. The first problem before was while we were watching, the TV was flickering then goes off. So I opened the back of the TV and figured out that the fuse was blown. After replacing the fuse when I turn on the TV the fuse immediately blown. So I've suspected that there has a short somewhere in the Power Supply. I tested the two mosfet STP9NK50ZFP and it was shorted so I replaced the two with P10NK60ZFP as an alternative because I can't find an exact model of that mosfet. As I turn on the TV again the TV opened but the screen flickers again and the TV goes off again. So I've check the power supply and the two mosfet that I've replaced become shorted again and the 3.15A fuse also blown.
I've read the recommendation of some expert of this group to make a lamp automatic current limiter. So I buy again the two mosfet and replace the fuse and plug the TV to the automatic current limiter when I've turn on the TV the lamp lights up becomes bright and the light is flickering. I've test with multimeter some parts and it seems ok. Can somebody help me how to troubleshoot the power supply.

POWER SUPPLY MODEL: BN44-00197B

Many thanks to you all.

[renzy101]

Re: SAMSUNG LA40A450C1XXP Power Supply Problem

Latest development in troubleshooting my LCD TV Power Supply.
Replaced the following parts (highlighted in green at the board):
STP9NK50ZFP mosfet = 2 pieces
IPW50R199CP Power Transistor
PS2561AL Photocoupler = 3 pieces

Still no luck in fixing this power supply.
I have some question to clarify if somebody has time to answer.
1. When the power supply is at standby mode the two big capacitor (CP802 and CP803) at the center has a 315V reading is that normal in standby mode?
2. When I take the mosfet 2SK3532 (QM802- Highlighted in red) when I turn on the power supply the lamp automatic current limiter does not lights up. but when I check the 2SK3532 it seems the reading is ok. Is the 2SK3532 mosfet needed to power the Power On/Off and STB5.3V when powering on the board?

Many Thanks for all your Help.

[budm]

Re: SAMSUNG LA40A450C1XXP Power Supply Problem

The 3.15A fuse is for the backlights inverter circuit, you can leave that fuse off the board for now so you can check and verify if the standby power supply is working or not when you run the power supply board by itself which mean you will have to put QM802 for the standby SMPS back in place.
The DC Voltage on the main filter cap in standby mode will be about 1.414 x AC line Voltage.

[renzy101]

Re: SAMSUNG LA40A450C1XXP Power Supply Problem

Thanks for your help Sir.

I put QM802 back and remove the 3.15A fuse.
The DC Voltage on the main filter cap 1.414 x 220V AC line Voltage= 311.08 DC Volt, approximate reading is 312 DC Volts in the capacitor CP802 and CP803. Whats the next step Sir.

[budm]

Re: SAMSUNG LA40A450C1XXP Power Supply Problem

Well, find out if you have any standby Voltage (STB5.3V) on the cold side of the standby power supply, see schematic.

[renzy101]

Re: SAMSUNG LA40A450C1XXP Power Supply Problem

Well, find out if you have any standby Voltage (STB5.3V) on the cold side of the standby power supply, see schematic.

I've tested the pin STB5.3V but the multimeter reading is 0V but when I put back the 3.15V fuse I get a reading of 5.2V is there a problem in my Standby mode.