Samsung LN40B550 turning off after 5 min.

[gabik111]

Hello everyone!
I got Samsung LCD LN40B550 K1F that is shooting down after 5 minutes of work. Result of powering off is overheating of STR-W6252 in PSU unit (BN44-00264B with LCD inverter integrated). When I unload capacitors and cool down STR it can turn on but after 4-5 minutes the same problem. I'm trying to find why STR is overheating. When I attatched larger radiator to STR it was working longer , but this is not a solution. PSU or whole TV schematic will be appreciated.
Any ideas?

[PlainBill]

Re: Samsung LN40B550 turning off after 5 min.

The service manual is here. It may not have a schematic of the power supply.

Pictures help us help you.

PlainBill

[gabik111]

Re: Samsung LN40B550 turning off after 5 min.

Site cannot be open due to some connection time limit... I'll try later. Anyway thanks for info. I'll post a message when I will find a solution.
Thx

[gabik111]

Re: Samsung LN40B550 turning off after 5 min.

Problem solved. I replaced all caps on the board and found shorted diode near STR-W IC. After replaced diode everything back to normal.

[tvtimmy]

Re: Samsung LN40B550 turning off after 5 min.

Where is the location number on the board, and, what was the value of the diode used?

[budm]

Re: Samsung LN40B550 turning off after 5 min.

Where is the location number on the board, and, what was the value of the diode used?

What is your board number, bn44-xxxxxx?

[tvtimmy]

Re: Samsung LN40B550 turning off after 5 min.

Bn44-00199a

[halfwayhillbilly]

Re: Samsung LN40B550 turning off after 5 min.

I am having a similar problem with my Samsung LN40A500T1F TV. While it doesn't overheat, it will go through several reboots before it finally turns on. Once it finally comes on it seems to work fine. I replaced all the large electrolytic caps in the 5.1 VDC and 13VDC circuits. Attached is the schematic for the power supply board (BN4400199a) Also attached is a screenshot where I've highlighted all the caps I replaced.

The 13 Volt supply will start at 14.1 VDC, then dip to 12.4 VDC and go back up to 14.1 VDC during the reboots, and will settle around 12.42 volts when the TV finally turns on.

The 5.1 volt supply is at 5.07 VDC but seems to have a lot of noise riding on it. Attached are 2 photos from my scope: the first with it plugged in but powered off, the second with it powered on.

So, my questions are: could this noise be causing my problem? If so, any suggestions on what else I should replace? If not, what else could be causing the multiple reboots?

[budm]

Re: Samsung LN40B550 turning off after 5 min.

Try solder in 100uf 16V LOW ESR in parallel with C102.
https://www.badcaps.net/forum/showth...208#post525208
https://www.badcaps.net/forum/showpo...&postcount=129

[halfwayhillbilly]

Re: Samsung LN40B550 turning off after 5 min.

Try solder in 100uf 16V LOW ESR in parallel with C102.
https://www.badcaps.net/forum/showth...208#post525208
https://www.badcaps.net/forum/showpo...&postcount=129

OK thanks. Can you help me figure out which Cap that would be in the BN44-00199A board? The schematic was in my last post. I don't see a C102 and am not exactly sure what that equates to in this circuit?

[budm]

Re: Samsung LN40B550 turning off after 5 min.

SMD CAP C102 is on the bottom side of the main board.

[halfwayhillbilly]

Re: Samsung LN40B550 turning off after 5 min.

Thanks! I found it and added the cap. seems to be working!

[budm]

Re: Samsung LN40B550 turning off after 5 min.

Thanks! I found it and added the cap. seems to be working!

Great, please give the follow-up to see how long it holds up.

[Gonnafix]

Re: Samsung LN40B550 turning off after 5 min.

My apologies for posting here, I'm a new member and can't post a new thread yet. I have a Toshiba 39L22U LED TV that isn't powering up. No lights at all. It just turned off by itself during our last episode of Narcos.. I've also looked everywhere for a service manual to no avail. This site has one reference to this model. Any help would be greatly appreciated!

[jason123]

LN40B500P3F Question

Hi there, I don't know if this belongs here or in new thread.. I have a Samsung TV LN40B500P3F, and it doesn't turn on. Has power and Red LED blinks 5 times when hitting the power button.

Standby and all voltages I checked on board, seem to be within tolerance.
I tried disconnecting the T-CON board, and not luck. The same blinking ritual.

One of the inverter transformers has a "hot" spot on the outside. Secondary voltage are slightly higher than the rest of the transformers. The puzzling part is the "Blue Transformer" on the BN44-00264B power board. The lowest secondary windings seem to be open. I've seen others with the same reporting. Can anyone verify that you have about 1.2 k Ohm across each of the secondaries of that transformer? I can buy one and replace what I have, I'm just curious if it's worth the effort.

Any suggestions / ideas on where to go next with the troubleshooting?
I can't find the schematic for the BN44-00264B (I found the A suffix and I'm assuming they're similar? any one knows for sure?)
Thanks

[budm]

Re: Samsung LN40B550 turning off after 5 min.

We need the pictures of the whole backside of the TV so we can see how all the boards are connected together and pictures of the suspect transformer.

[budm]

Re: Samsung LN40B550 turning off after 5 min.

BTW, the blue inverter tranasformer only has ONE high Voltage windings, the other inverter transformers have TWO high Voltage winding.
This is the board you have, right? Pictures provided by shopjimmy.

'Standby and all voltages I checked on board, seem to be within tolerance.': And did you check all the command signals for the main board feeding to the power supply-inverter board, they are all OK? We need to see the readings.

BTW: 'Secondary voltage are slightly higher than the rest of the transformers.' How did you manage to read the High Voltage of over 1000VAC on your meter?

[jason123]

Re: Samsung LN40B550 turning off after 5 min.

budm, thanks for the reply. I'll get the photos, but it's identical to the photos you kindly provided. I'll take more of the whole TV.
I didn't measure the 1000V rather when the TV backlight is off, I measured the AC voltage out of the secondary of all transformers.. it was not 0V, rather, 2.3 VAC except the suspect transformer.. it was 2.5 VAC

No, I have not measured any of the command signals. I was just able to read the part number of the main PCF controller, to be BD9893F I believe. Though I have the datasheet, it doesn't say a lot about the function of the pins. Not in details I am familiar with at least. Anything in particular you'd like me to measure?
Thanks

[budm]

Re: Samsung LN40B550 turning off after 5 min.

You can verify if the PFC Voltage booster circuit is working or not by measuring the DCV between the two legs of the main filter cap on the primary side, it should be close to 400VDC when TV is turned on.
If you do have the boosted Voltage then you know the PS-ON is present.

[jason123]

Re: Samsung LN40B550 turning off after 5 min.

Sure, the voltage on the large caps is 392V when on