Samsung LE37C630K1W - Random power on

[JavierC]

Make: Samsung
TV Model: LE37C630K1W
PSU Model: BN44-00339B
Main Model: BN41-01443A
Inverter Model: 4H.V2988.071/A1 E206453 V298-5XX*


A friend of mine gave me this TV as he got fed up and bought a new one.

He said the TV turns off randomly and will not turn on again for a few hours/days. Eventually it turns on again, and sometimes fails straight away, other times it worked just fine for a few weeks/couple of months until it happens again.

When I plugged in the first time, it worked! and I managed to enjoy a fully functional tv for 3 days, but then I tried to turn it on and heard the samsung tune, but i wouldn´t turn on, 5 seconds later the samsung tune again, and so on.

I thought it was a badcap problem, and even though all the caps looked ok, I replaced them all and cleaned the power board. Problem still there.

Once I plug the TV to the mains, I can hear the Samsung start-up tune, the backlight flashes once and it turns off, after 5 seconds this repeats.

When disconnecting the Main card from the Power card, as I plug in the TV, the backlight keeps blinking and no power off. (only once or twice, when plugging the tv to the mains, the backlight stayed on)

When disconnecting the Inverter from the Power card, as I plug in the TV, I get audio (and presumably video as well). No power off.

I get the following readings:

-With both Inverter and Main disconnected,

Between terminals of CP801 (120uF 450V) : 380 V

CNI801 - pin 14 : 25 V

CN 802 - Pin 17: 12 V
CN 802 - Pin 15: 5 V

-With both Inverter and Main connected,

Between terminals of CP801 (120uF 450V) : 380 V - always

CNI801 - pin 14 : 25 V, then drops to 20V after backlight blinks, then recover to 25V

CN 802 - Pin 17: 12 V then drops to 0V after backlight blinks, then recover to 12V

CN 802 - Pin 15: 5 V then drops to 0V after backlight blinks, then recover to 5V


I read somewhere that FAN7530 could be causing the problem, but I have no idea about this. Anyway, I checked the resistance of RP801 to RP804 and they seem to be OK.


Any help would be much appreciated.

[sordids999]

Re: Samsung LE37C630K1W - Random power on

clear pictures of the boards from the back of the tv might help

[JavierC]

Re: Samsung LE37C630K1W - Random power on

There you go

[JavierC]

Re: Samsung LE37C630K1W - Random power on

Browsing the net, found a website in the UK selling a "POWER SUPPLY REPAIR KIT BN44-00339B QP801 QP802 FAULTY"

Power supply repair kit? Really? Do this mean that those are the only components needed for fixing this specific Power supply?


http://www.ohmsupplies.co.uk/epages/...on=ViewProduct

[tom66]

Re: Samsung LE37C630K1W - Random power on

Well, no. That will fix only one fault. If it is those FETs, more likely the set would be completely dead with a blown fuse.

[JavierC]

Re: Samsung LE37C630K1W - Random power on

Today I went back to my repair project. After a few days disconnected, the TV started on the first attempt. I Actually managed to turn it on and off some 5 times,and took a few more measures. But then the problem came back.

With the TV on, the inverter board makes a buzzing noise, which I believe is louder than it should be. Couldn´t identify which of the inverter transformers is the culprit of the noise though.

The electrolytic capacitors on the inverter board measured the same voltage, around 20 V when the TV worked fine.

The resistance on the inverter transformers secondary is (From Pic 5):
Bottom right transformer 1,2K 1,2 K
Bottom middle tTransfromers 2,47K
Bottom left transformer 1,16K 1,16 K

Does the middle transformers have a higher resistance for any specific reason? Is the bulb they feed different from the others?

Following another post, I found that the IC oz9937 is the CCFL controller. I followed pin, 14 which is the timer and had 0 V. Is this IC responsible for the INV_ERR signal?

I found INV_ERR to be around 1 V when the TV has the problem (Alas didn´t measure it when the TV was OK).

Any ideas?

Thanks

[JavierC]

Re: Samsung LE37C630K1W - Random power on

Update !

I re-soldered the joints of the transformers and MosFETS of the Inverter board, and now the TV turns on more frequently. Sometimes Tv starts at the first attempt, other times the backlight blinks two or three times during the startup cycle, and eventually stays on

I took some more measures and found that with the Power Supply board disconnected from the Main and Inverter boards, there are 1,2 Volts on the INV_ERR pin. Shouldn´t this be 0V ?

Then, when I connect the Main and Inverter Boards, and plug in the TV to the mains, INV_ERR measures 1,8V for a couple of seconds, while the backlight is still off, and when the backlight turns on , it drops to 0,7 V and stays there.

Is probably QM802 (MMBT2222A) on the Power board not working properly? How can I test this?

Regards,

[JavierC]

Re: Samsung LE37C630K1W - Random power on

Today I decided to do some more testings on my TV.

With the Power board only connected to the Inverter, and not he Main, I disconnected the INV_ERR cable from the ribbon and didn´t connect it to anything.

Then I plugged the Power board to the mains, and could verify that the INV_ERR pin on the Inverter side measures 0V, but the same pin on the Power board measures 1,2V.

Which means the problem is definitely on the Power board.

Now, from here I´m lost. What should I do next?

Any help would be appreciated.

Thanks

[JavierC]

Re: Samsung LE37C630K1W - Random power on

I forgot to mention that, the backlight turned on during this, and also I believe the buzzing noise from the inverter was almost imperceptible.

[JavierC]

Re: Samsung LE37C630K1W - Random power on

After reading some PDFs about diagnosing PSU and LCD TVs, and studying some basics about switching power supply, and after analysing the PSU schematics, I think the problem could be the Half-Bridge Resonant Converter, which is the FSFR1700US.

Have anyone experienced a problem with this power switch before?

I will also replace CS 801 1250V 22nF

[JavierC]

Re: Samsung LE37C630K1W - Random power on

Up

[mirmigki]

Re: Samsung LE37C630K1W - Random power on

Hi JavierC,

do you have any news regarding the fix?

I have the same TV and the restart problem keep getting more often now.

Thanks,
George

[veryoldman]

Re: Samsung LE37C630K1W - Random power on

Hello JavierC,

What stage your repair?

I have almost the same Samsung TV LE37C650L1W and fully the same problem with reboot. After several months reboot 1-2 times before it becomes normal, now finally he stopped and only restarted.

[saratoga]

Re: Samsung LE37C630K1W - Random power on

Salve, stesso problema con LE32651
ho sostituito IC STM4820
guasto risolto
Ciao

[saratoga]

Re: Samsung LE37C630K1W - Random power on

Sorry,
TV Model: LE32B651
PSU Model: BN44-00261A

problem : Random power on/off

solved replacing STM4820 and cap. CM852/1200/25/105
Ciao

[mirmigki]

Re: Samsung LE37C630K1W - Random power on

Hello,

Did anyone manage to fix the tv? LE37C630K1W
saratoga seems to have a different model and psu.