Samsung UE40F6400AY relay sound and reboots continuosly

[Luis8]

Hi guys,

I friend of mine bring to me this TV because it started to reboot continuosly.
Sometime when the TV is really cold it startup correctly but when we shut it down and try to turn it on again it is stucked in bootloop.

When the TV fails to start i can hear the sound of a relay triggered in the PSU.

I tried to do some measurement and voltages are present in the connector to the mainboard but being the power supply intermittent i don't know if i can trust these measurement.
By the way if i disconnect the PSU from the mainboard the LED backlight stays on, so i think that the problem must be in the PSU.

Do you have any suggestion where to look at?
The PSU model number is BN44-00622B.

Thanks a lot!

[nomoresonys]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

More than likely the problem IS the mainboard.

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Can you give more details on that please?
As I wrote if I have just the PSU alone connected the led back-light stays on but the PSU have the same behavior (relay clicking each 2 seconds and voltages drop down).

With this behavior I think that i should consider just the PSU... Can you suggest something to check?

Thank you so much!

[nomoresonys]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Ok, backlight on is good, relay clicking is probably odd, check over all your solder joints, look real close to see if any are bad/cold.

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

I already did that but no luck unfortunately... Can I make some measurement or photo to help the analysis? I don't have so much ideas on how to proceed further. Any help will be really appreciated

[nomoresonys]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Heat up your powerboard with a hairdryer see if it starts up or stays on longer, be sure and heat the electrolytic capacitors, see what happens.

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

I did it but no luck, it seems that most of the time that i am able to turn it on is when it is cold i don't know if it makes sense.

I would like to know the approach that you guys would use in this scenario where giving the power supply intermittent it's impossible to make any valuable measurement...

Anything else that i can try/check?

[dick_barton]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

I already did that but no luck unfortunately... Can I make some measurement or photo to help the analysis? I don't have so much ideas on how to proceed further. Any help will be really appreciated

Photo's would be a good idea.

If when it's cold it starts then can you use a can of freezer spray (or inverted can of air duster spray) and use it to cool components on the power supply (set off) and then power up to see if the set comes up to attempt to identify the component which may be causing the issue.

Have you checked all the solder joints are good on the underside and there are no cracked joints.

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Photo's would be a good idea.

If when it's cold it starts then can you use a can of freezer spray (or inverted can of air duster spray) and use it to cool components on the power supply (set off) and then power up to see if the set comes up to attempt to identify the component which may be causing the issue.

Have you checked all the solder joints are good on the underside and there are no cracked joints.

Yes i checked the joints and re-do a lot of them to be sure.

I made some other measurement and testing and i was wrong, with the mainboard disconnected from the PSU the led lights are blinking because of the relay shutting of the power. When i am lucky and the TV starts correctly it seems that the backlight strips are all good.

Here i attached a picture of the front and back of the PSU, i recorded also a video to show the clicking issue:
https://youtu.be/-IDE-OUGtZA

Please help

[dick_barton]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Your video is not "public" so cannot be viewed at the moment.

[miroja]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

At first, i will put my answer from private message to keep continuity in my following answers:

.. it was a year ago...
Are you sure that problem is in The IC? Did you exclude rest of TV? (main board, backlight strips, power supply itself?

Those IC's are for Led strip current source, bright regulation, uver-current and over-voltage protection only.

I eliminated signal "output protection" from first IC, afterwards from second IC. In my case, PSU stop click relay when signal from first IC was interrupted.

Do you have schematic of this PSU/backligt current source board? I found very useful description of board in Russian magazine Ремонт и сервис №5 2018 if a am not mistaken :-)

As far as i remember i put PSU board out of the window for a hour ( it was on february, i am living in altitude 650m) - you can use refrigator also - . After that i use hair dryer for heating to confirm selection of broken IC.

[R_J]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

You likely have the standby +5v droping, Check the voltage across CS851. I would also replace CS804, the top looks slightly bulged and CS806. If the small caps don't fix it try replacing CS851

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Your video is not "public" so cannot be viewed at the moment.

Made it public, please check it.

At first, i will put my answer from private message to keep continuity in my following answers:

.. it was a year ago...
Are you sure that problem is in The IC? Did you exclude rest of TV? (main board, backlight strips, power supply itself?

Those IC's are for Led strip current source, bright regulation, uver-current and over-voltage protection only.

I eliminated signal "output protection" from first IC, afterwards from second IC. In my case, PSU stop click relay when signal from first IC was interrupted.

Do you have schematic of this PSU/backligt current source board? I found very useful description of board in Russian magazine Ремонт и сервис №5 2018 if a am not mistaken :-)

As far as i remember i put PSU board out of the window for a hour ( it was on february, i am living in altitude 650m) - you can use refrigator also - . After that i use hair dryer for heating to confirm selection of broken IC.

I am not sure that the problem is the IC. But i have the relay clicking also with mainboard and led disconnected so i think that the problem is in the PSU.
Curious to know, how do you eliminated the signal of output protection? By destroying the track on the pcb?
I attached the schematic of the PSU.

You likely have the standby +5v droping, Check the voltage across CS851. I would also replace CS804, the top looks slightly bulged and CS806. If the small caps don't fix it try replacing CS851

Just checked the voltage on CS851 i have 5.3v and they are stable also when the relay clicks (measured with an analogic multimeter). I tested all the big caps on the low voltage of the PSU with an ESR meter but they are ok. I didn't checked the small one in the high voltage section of the PSU to be honest. I will test with the ESR meter CS804 and CS806 and update with results.

Thanks a lot to everyone, do you have other ideas?

[miroja]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

Main PSU have to be switched permanently ON also without connected main board, but backlight have to be connected and 100% OK.

If you carefully checked LED strips an you are sure that there is no interrupted LED, no shortcuted LED on any strip, please skip next few sentences.

There are four separate backligt channels. First channel needs for feeding apr. 45V/270mA, next 3 channels apr. 90V/270mA. Last three channels are two the same LED strips as for first channel, but connected serially. For backlight is used 7 strips in total in this TV.
(see picture from magazine mentioned below)
Each IC is responsible for two channels. First half of first IC (9101) generate apr. 45V, next half apr.90V, second IC (9102) 90V per each channel. Each IC has output over voltage and overcurrent protection for LED strips feeding. In case of error LED strip is generated from appropriate IC error signal, which switch off main PSU. TV is switching off, after a few second switching on ad again...


I have to apologize, magazine number in my first answer is not correct. I repaired this type of TV only once a year ago.. ;-) i forget it.. :-)

The correct one is Ремонт и сервис №8 2018 from page no. 5. There is really nice and deep described PSU itself, in magazine Ремонт и сервис №9 2018 from page no. 4 is described specially DC-DC converter for backligt LED strips feeding also with over protections (output over voltage and overcurrent protection for LED strips feeding).

What is your nationality? Can you read an understand Russian text?

Sorry for my English, it is not my native language..

[R_J]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

There are only 2 things that will cause the relay to turn on and off, either the supply voltage for it is dropping or the Relay_on line is not connecting to ground because QS861 is being turned on and off.
If the main board is disconnected the relay should not pulse and the power supply should turn on.

By the way if i disconnect the PSU from the mainboard the LED backlight stays on, so i think that the problem must be in the PSU.

If the power supply turns ON and the backlights stay ON, this means the power supply is OK and the problem is with the main board

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

You likely have the standby +5v droping, Check the voltage across CS851. I would also replace CS804, the top looks slightly bulged and CS806. If the small caps don't fix it try replacing CS851

I checked CS804 and CS806 with the ESR meter and they are ok but to be sure i tried to replace them. No luck unfortunately, i have the same behavior. Do you have any other suggestion?

Main PSU have to be switched permanently ON also without connected main board, but backlight have to be connected and 100% OK.

If you carefully checked LED strips an you are sure that there is no interrupted LED, no shortcuted LED on any strip, please skip next few sentences.

There are four separate backligt channels. First channel needs for feeding apr. 45V/270mA, next 3 channels apr. 90V/270mA. Last three channels are two the same LED strips as for first channel, but connected serially. For backlight is used 7 strips in total in this TV.
(see picture from magazine mentioned below)
Each IC is responsible for two channels. First half of first IC (9101) generate apr. 45V, next half apr.90V, second IC (9102) 90V per each channel. Each IC has output over voltage and overcurrent protection for LED strips feeding. In case of error LED strip is generated from appropriate IC error signal, which switch off main PSU. TV is switching off, after a few second switching on ad again...


I have to apologize, magazine number in my first answer is not correct. I repaired this type of TV only once a year ago.. ;-) i forget it.. :-)

The correct one is Ремонт и сервис №8 2018 from page no. 5. There is really nice and deep described PSU itself, in magazine Ремонт и сервис №9 2018 from page no. 4 is described specially DC-DC converter for backligt LED strips feeding also with over protections (output over voltage and overcurrent protection for LED strips feeding).

What is your nationality? Can you read an understand Russian text?

Sorry for my English, it is not my native language..

If you can view my video: https://youtu.be/-IDE-OUGtZA here just the PSU alone is connected to the power supply and i have the relay clicking issue anyway. If i try with the main board disconnected but backlight connected i have the LED that turn on and off following the supply voltage.
Sometimes the TV turn on without problems, if i had some burnt led this situation will be possible? How i can check the led without open the TV frame?

By the way i think that the PSU alone should run without issue also if i disconnect Main and LED light, so i am working on the PSU alone.

Unfortunately i don't undestand russian, but i will try to find this magazine and translate it with the help of Google.

I really need to fix this TV so please any additional help will be really appreciated!

[miroja]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

By the way i think that the PSU alone should run without issue also if i disconnect Main

Yes, i agree too

...and LED light, so i am working on the PSU alone.

I am not sure, because:
Please see attached picture (a few pages from magazine).
In red marked square is described under voltage protection Vdrv1. If is less than 18V The protection is activated, IC is switched off.
In yellow marked square is described over voltage protection for LED strip no. 1. If is there more than 87V The protection is activated, IC is switched off.
I think that google translator is not easy way in this case. I have found only pdf "bitmap" scan of the magazine. No OCR scan.

What happends with output voltage for LED strip if is the strip disconnected/broken-interrupted ?

Did you measured voltage at pins 25 IC DC-DC converters?

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

By the way if i disconnect the PSU from the mainboard the LED backlight stays on, so i think that the problem must be in the PSU.
If the power supply turns ON and the backlights stay ON, this means the power supply is OK and the problem is with the main board

I corrected this statement with the following in a later post, unfortunately when i wrote that the PSU worked and made me to make fake assumptions.

I made some other measurement and testing and i was wrong, with the mainboard disconnected from the PSU the led lights are blinking because of the relay shutting of the power.

In fact if you see the youtube video that i uploaded i have on the bench just the PSU and you will hear the relay turn on and off.

There are only 2 things that will cause the relay to turn on and off, either the supply voltage for it is dropping or the Relay_on line is not connecting to ground because QS861 is being turned on and off.

I measured the pins 3 and 4 of the relay:
- A5V signal drops when the relay turn on and off.
- RELAY_ON seems to be 5v

I saw QS861 that you are mentioning and it is an SMD mosfet, i will try to test it with the multimeter and let you know. What additional test can i do to understand the fault better?

I am infinitely grateful to you, i am learning new things with your help!

[R_J]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

- A5V signal drops when the relay turn on and off.

A5V is not a signal, it is the standby voltage and if it drops that is your problem, Relay_On should be near 0 volts when the power supply is ON
The mosfet (QS861) is likely ok or the relay would not turn on at all or would be on all the time.

[Luis8]

Re: Samsung UE40F6400AY relay sound and reboots continuosly

A5V is not a signal, it is the standby voltage and if it drops that is your problem, Relay_On should be near 0 volts when the power supply is ON
The mosfet (QS861) is likely ok or the relay would not turn on at all or would be on all the time.

I am sorry i wasn't precise, i meant A5V voltage
I made other measurements today and i have stable voltage across DS858C and CS851 but i have 0 volts across CS854.

The only accused can be QS851, it doesn't have drain and source short-circuited and i am not sure on how to effectively test it with the multimeter but i think it is the culprit. Do you agree with me?

It never happened anymore that the PSU was able to start correctly but can a mosfet be affected by thermal malfunction? If so it is the first time that this happen to me.

Thank you very much for your help and patience