Samsung UH50EH5300FXZA, help with a transformer?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I made a change in my post, I ment QM808
To check this transistor, use diode test, with one probe on the base, check the collector then emitter, should read around .6xx, then reverse the leads and should read close to open. Then check between collector and emitter, this should read open both ways (depending on other in circuit components)

QM808 checks good.

EDIT/ADD: Is there a way to fire up the board out of the TV for actual voltage testing? I see several places on the back of the board that look like test points. Maybe if I test for voltage that way we will find the culprit?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

So what DC V do you you have on each pin of the Transistor? GND ref will be the negative leg of the main filter cap.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

So what DC V do you you have on each pin of the Transistor? GND ref will be the negative leg of the main filter cap.

QM808 voltages main cap ground referenced:

Emitter: Started at 1.1v and slowly fell off to .79v
Base: 4.1v to 4.15v with an occasional rise to 5.3v
Collector: 3.92v to 4.2v with an occasional rise up to 5.2v

Voltage at A5V is now gone

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

You can run the board out of the tv without a problem. Like I said before, the board will try to turn all the supplies on unless you ground the PS_ON pin.
So ground PS_ON again and see if you have A5V
This power board has 3 seperate power supplies. The standby/run supply for the A5V. It also supplies the B5V and B12V when turned on.
Then there is the PFC power supply. and the LED driver power supply

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

You can run the board out of the tv without a problem. Like I said before, the board will try to turn all the supplies on unless you ground the PS_ON pin.
So ground PS_ON again and see if you have A5V
This power board has 3 seperate power supplies. The standby/run supply for the A5V. It also supplies the B5V and B12V when turned on.
Then there is the PFC power supply. and the LED driver power supply

Ok I will pull the board and re-test with it out. First will be to verify whether or not A5V exist at its pin with PS_on grounded.

After that, one of your concerns was whether or not VCC was present on PIN8 of the LED controller IC. Should I check that next, and then measure test points for voltage in the areas of suspicion? I will record these with the hope it will help troubleshooting.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

You can run the board out of the tv without a problem. Like I said before, the board will try to turn all the supplies on unless you ground the PS_ON pin.
So ground PS_ON again and see if you have A5V
This power board has 3 seperate power supplies. The standby/run supply for the A5V. It also supplies the B5V and B12V when turned on.
Then there is the PFC power supply. and the LED driver power supply

A5V is a steady 5.2v with PS_on grounded, chassis ground reference

You are correct R_J, VCC is missing on pin 8 of the LED controller IC.

Questions:

Pin 1 of the LED controller IC has 89 volts on it, reference earth ground

All pins of LP802CS have 166v. This is "sparkly joe", or the "transformer" I referenced in the original post.

There's no way these voltages could be correct, right?

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

LP802CS is a COIL it is NOT a transformer. It is one single piece of wire, It comes direct from the bridge rectifier so 160 volts is correct, on all leads.
The ic I was refering to was ICP801S, It is the PFC circuit, this is the circuit that boosts the voltage coming from the bridge rectifier from 160 volts to 400 volts on the main filter cap CP806S
The LED controler/driver ic is the ic near the led plug.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Please check the resistance between point A and point B for me to see if it shows < 1 Ohm.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

LP802CS is a COIL it is NOT a transformer. It is one single piece of wire, It comes direct from the bridge rectifier so 160 volts is correct, on all leads.
The ic I was refering to was ICP801S, It is the PFC circuit, this is the circuit that boosts the voltage coming from the bridge rectifier from 160 volts to 400 volts on the main filter cap CP806S
The LED controler/driver ic is the ic near the led plug.

Please check the resistance between point A and point B for me to see if it shows < 1 Ohm.

Thanks R_J. I think budm is referring to this in his last post too.

Resistance is not less than 1 ohm. It is 22.5ohms. I'm guesing we just checked that leg of the IC for short?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

No, I am looking for the switched Transistor that supplies the Voltage to VCC pin 8 of the PFC IC, I could not see QM808 that RJ is referring to.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Check the JRM803 0Ω resistor next to point B. QM808 is the transistor at point B, it is marked on the other side of the board

I am guessing DM809 diode and CM809 cap. are the supply for the that transistor?

QM807 is likely another switch.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Hi Rj, so that is QM808 then, I was tracing the bottom side of the board to find out how that Transistor is connected to pin 8 of the PFC IC.
I also expect one of the leg will show 15 ~ 20 vdc when PS-ON pin is grounded.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

it looks like CP812 is the filter cap for the PFC IC pin 8.
I also wonder if these Lytics caps are OK: CM809, CM814, and that CP812.
I also cannot clearly see the RP824 value, it has one end connected to the + leg of cap CP812, the + leg of the CP812 should also show <1 Ohm to point B the leg of QM808.
BTW QM808 P/N? Is it NPN?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Check the JRM803 0Ω resistor next to point B. QM808 is the transistor at point B, it is marked on the other side of the board

I am guessing DM809 diode and CM809 cap. are the supply for the that transistor?

QM807 is likely another switch.

JRM803 is straight through, zero resistance.

Hi Rj, so that is QM808 then, I was tracing the bottom side of the board to find out how that Transistor is connected to pin 8 of the PFC IC.
I also expect one of the leg will show 15 ~ 20 vdc when PS-ON pin is grounded.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

it looks like CP812 is the filter cap for the PFC IC pin 8.
I also wonder if these Lytics caps are OK: CM809, CM814, and that CP812.
I also cannot clearly see the RP824 value, it has one end connected to the + leg of cap CP812, the + leg of the CP812 should also show <1 Ohm to point B the leg of QM808.
BTW QM808 P/N? Is it NPN?

RP824 is marked 022, there is also a line above the 2, thinking this is 220? I have not checked CP812 for capacitance but can do.

QM808 is MPS751Y, datasheet says it is PNP

Positive leg of CP812 to point B as marked on the previous picture is .4ohms. From the + of CP812 to leg 8 of the PFC IC is 22.5ohms

Caps CM809 and CM814 have proper capacitance out of circuit.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

If you look at the schematic of the BN44-00520C, there is a 22Ω between the transistor switch and the pfc ic vcc, which would make sense.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

If you look at the schematic of the BN44-00520C, there is a 22Ω between the transistor switch and the pfc ic vcc, which would make sense.

On RP824 there is 022 with a line on top. Does this line denote "this side up" to read the value properly?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

When PS-ON pin is grounded, I do expect at least 12V on the Emitter pin of the QM808 (PNP, It is turned off when PS-ON is grounded).

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

When PS-ON pin is grounded, I do expect at least 12V on the Emitter pin of the QM808 (PNP, It is turned off when PS-ON is grounded).

Redacted.

Redacted again

So what supplies voltage to pin8 of ICP801S with PS_on grounded? Is there supposed to be voltage there with PS_on grounded or were we just checking for a good pathway with the resistance test?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

The Voltage on the Emitter is generated by the AUX winding of the transformer which is fed to the switched Transistor QM808 Emitter (because it is PNP transistor), there will be no output on the Collector until PS-ON is present. The PFC IC running Voltage is around 12V.