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

[waakye]

I was reading it all wrong. when the set is forced on I read the following:
Short pin 4 and 3 on the opto. Am reading .188vdc on pin 4 and pin 3 reads 6.37vdc.

Set is not forced on
Short pin 4 and 3 on the opto. Am reading .249vdc on pin 4 and pin 3 reads 17vdc

set is not forced on .
pin 4 and 3 on the opto not shorted. Am reading 18.7vdc on pin 4 and pin 3 reads 2.02vdc.

Set forced on
pin 4 and 3 on the opto not shorted. Am reading 20.5vdc on pin 4 and pin 3 reads 99.89millivolt.

Thanks.
I am interested in what next to try.

[R_J]

I think you have the pins on the opto coupler mixed up, The supply voltage that comes from the standby transformer connects to pin 4 of the opto, so there is no way for pin 3 to be higher than pin 4.
The standby transformer supplies this voltage via DS802, JP1021, RS806 and the filter cap is CS804 (check this cap)

[waakye]

when the Power Supply is forced on.
I read the following:
Short pin 4 and 3 on the opto. Am reading 6.25vdc on pin 4 and pin 3 reads 6.25vdc.

Power supply is not forced on
Short pin 4 and 3 on the opto. Am reading 17.11vdc on pin 4 and pin 3 reads 17.11vdc

Power supply is not forced on .
pin 4 and 3 on the opto not shorted. Am reading 18.7vdc on pin 4 and pin 3 reads 2.09vdc.

Power supply forced on
pin 4 and 3 on the opto not shorted. Am reading 20.5vdc on pin 4 and pin 3 reads 94.6millivolt.

I also change the cap CS804 before executing the tests above.

Something else I can try?

[R_J]

Something is killing that 20 volts, Does the standby 5 volts stay up when you short pins 3 & 4 of the opto? or does it also drop

[waakye]

When I short pin 3 and 4 and force the power supply on, A5V at CNM803 is always at a steady 5.33vdc. both A5V is at 5.33vdc.
Thanks

[R_J]

Check the diode, resistor etc. on that line from the standby transformer, that voltage should not be dropping, it is supplied by the standby transformer. Maybe check the voltage right at the diode DS802. Also check that the standby transformer winding is not open.

[waakye]

Is the standby transformer TS801S? I looked at the Diode DS802 and am measuring .475 in diode mode. Is it possible for you to get me a sketch on how I can test circuit. The DS802 shows a reading of 21.2vdc when I measure at the side with the band. The other side of the diode measure 0v.

[waakye]

Is the standby transformer TS801S? I looked at the Diode DS802 and am measuring .475 in diode mode. Is it possible for you to get me a sketch on how I can test circuit. The DS802 shows a reading of 21.2vdc when I measure at the side with the band. The other side of the diode measure 0v.
The part of that transformer circle red is showing a reading of 0 volts. Im really confused about where the 21.2vdc is coming from.

[R_J]

The 21 volts comes from that transformer, transformers produce A/C (in this case it is at around 30khz) then the diode rectifies it into DC. Did you check if that 21 volts stayed up when you shorted pins 3&4 of the optocoupler

[waakye]

When the pin 3 and 4 are shorted at the optocoupler and the power supply is forced on. The 21 volts drops to 6.25vdc.

[waakye]

My guess is probably the CS808 but I do not know the value of that capacitor

[waakye]

I also noticed that the voltage from pin 3 of the optocoupler to out of the resistor RS808 measures 1.7 volts even though the pin3 measure 17.11vds. the resistor has a 301marking on it.

[waakye]

The 301 value is 300 ohm.

[R_J]

Originally Posted by waakye

The 301 value is 300 ohm.

This is correct.

[R_J]

.

[waakye]

At this point am open to any ideas to try. It's just that the only place I can buy the power supply board is in Asia or Europe. That's sucks.