Samsung LN40B550 turning off after 5 min.

[bold_fusion]

Re: Samsung LN40B550 turning off after 5 min.

What is your board number, bn44-xxxxxx?

Hi @budm,

Quite simply, I can see that you are the savior of this forum... thanks! Okay for an additional question?

Like the OP of this thread, I have a Samsung Inverter Board BN44-00264B that happens to sit in my Old Samsung LN40B540 TV (trying to squeeze a few extra years out of it before the junk heap).

As I discussed in another recent post (sorry newb here, can't make new post AFAIK), the display is blinking-off for a few seconds at a time, while the audio is still functional. When I dial the Back-Light setting down to 0/10, the blinking off goes away; however, every so often the Back-Light setting will reset to 10/10 (!), and then the blinking off comes back until I re-apply the Back-List setting of 0/10 :-\.

Since I don't see any bulging caps or burn marks near any of the inverter transformers (checked the top of the 4 transformers, but didn't remove them to visually inspect the bottoms), I'm leaning towards one or more of the back-light CCFL lamps being burnt to a short, and thus a protection circuit is disabling the display for a few seconds at a time (?), as shown in this video:

https://www.youtube.com/watch?v=Dh01ZepjDp0

Also in the above video (which doesn't use the exact BN44-00264B but something similar), they appear to have a good way to simply bypass/disable the lamp which is drawing too much current; since I'm okay if one or a few of the lamps are turned off in the short-term, I'd like to try this fix.

However, I can't align the test points that the video author uses with his different board with the corresponding components/pads on my BN44-00264B.

Moreover, I'm so darn close to finding the schematic/circuit-diagram for it, but can't quite find it. I've found schematics online for BN44-00264A, BN44-00264C, and I was hoping they would be very similar, but the component label numbers are different :-\. Finally tonight, I found the Service Manual for the Samsung TVs containing BN44-00264B, but as the poster mentioned above, that discusses overall TV system diagnostics, but not specific component-level testing repair of the Inverter Board, BN44-00264B :-\.

I've attached a photo showing how I've read the Model Number BN44-00264B.

Is there any chance you might be able to find the BN44-00264B schematic/circuit diagram?

Any assistance *enormously* appreciated!

[budm]

Re: Samsung LN40B550 turning off after 5 min.

Thanks for the follow-up.

[jason123]

Re: Samsung LN40B550 turning off after 5 min.

Just an update... turns out one of the inverter transformers had a primary short.. I replaced it and I'm back in business.. thanks for the help.

[budm]

Re: Samsung LN40B550 turning off after 5 min.

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

So at least you do have PS-ON signal and the PFC is working.
So after 5 minutes, do you still get the 392VDC? If not, then need to find out if it is due to PS-ON drops out or the PFC drops out.

[jason123]

Re: Samsung LN40B550 turning off after 5 min.

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

[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.

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.

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?

[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.

[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

[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!

[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.

[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.

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

[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.

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.

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?

[tvtimmy]

Re: Samsung LN40B550 turning off after 5 min.

Bn44-00199a

[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.

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