Samsung 50uhd8550 standby led pressing power button does not turn TV on

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

It could be bad, How does DS811 check? It could be that the zener diode is bad. what are the markings on the zener?

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I changed the zener diode and I got 10.18volts at the base of the QS801.
DS811 reads .564.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Corrections. I read 8.86v on the base of QS801 which also read 10.12v on the pin 3 of the PCS802S

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Corrections. I read 8.86v on the base of QS801 which also read 10.12v on the pin 3 of the PCS802S

Well it could be that the zener is bad and zenering at about 10v or the optocoupler which when turned on should have the same voltage on pins 3 & 4.
The markings on the zener will tell you what the voltage should be. If you do have 10v on the base you should have about 10v on the emitter as well
When the power supply is forced on pins 3 & 4 of the optocoupler should be almost identical. You could try swapping PCM801S and PCS802S, I believe they are the same. Leave PCS801S alone as it is the feedback for the standby ic and that circuit is working.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I used an old Zener diode and it seems that whenever I force the set on the pin 3 on the optocoupler goes to 100millivolts. Pin 4 at the optocoupler is at 20.5v when I forced the set on. Do you it it might be the optocoupler or I should investigate on the DS811 diode?
Thanks and I really appreciate your help.

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Yes it could be the opto, You could try swapping PCM801S and PCS802S, I believe they are the same. PCM801S I believe is for the backlights
Don't swap PCS801S as it is the feedback opto for the standby ic which is working.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I will get on that tomorrow after my day job is over and report back. I really appreciate all your help. Whenever you are up in the East, Mtl I owe a few drinks.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I swapped PCM801S and PCS802S and am observing the same issue when the power supply is forced on pin 3 of the PCM801S shows 100mv. Pin 4 is around 20.5v. when the power supply is not force on am measuring 10.14v at the PCM801S pin 3 and 18.9v around pin 4.
What is the next step to look for.

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Check the cold side of the opto, This time use cold ground and check the voltage on pins 1 & 2 of PCS802S, In standby you should have voltage on pin 1 and aprox the same on pin 2, when forced on pin 2 should drop and there should be a difference of about 2v between pins 1 & 2 (this is what lights the internal led)

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Readings from the opto PCS802S without the set forced on. Pin 1 reads 1.88v, pin 2 reads .771v.
When the set is forced on I read the following values on the pin 1 and 2 of the PCS802S. Pin 1 reads 5.33v and pin 2 reads 4.65v.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

What can I verify now.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Any help?

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

What you can try is see if the opto PCS802S will turn on the VCC for the main ic, Monitor the voltage out of QS801 emitter (can be checked at JP1017 using JP1028 as hot ground) then using something to short PCS802S pins 3 & 4 and see if the voltage on QS801 emitter comes up to around 15~17 vdc.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Shorted pin 3 and 4 of opto PCS802. JP1017 read .714 volts DC. I believe the power supply is defective. I want to learn how to troubleshoot down to the components. Ebay has it but from China and shop jimmy is out of stock.
R_J I really appreciate your help.
Thanks

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Could QS801 be defective? It's harder to see the part number on it.

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I guess it could be, but not likely, the opto should still supply close to the vcc supply voltage to the base. It could be something like a DXT651 (used on other boards)

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

I am open to any suggestions.

[R_J]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

The voltage on pin4 should be around 20v, when you short pin 4 to pin 3 what does this voltage do? Check if CS808 is shorted, something must be killing that voltage.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

Short pin 4 and 3 on the opto. Am reading 6.35vdc on pin 4. I will verify the cap CS808 and report back.

[waakye]

Re: Samsung 50uhd8550 standby led pressing power button does not turn TV on

CS808 read .329microfarads