Samsung UH50EH5300FXZA, help with a transformer?

[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.

[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?

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.

[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?

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

[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.

[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?

[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.

[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?

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

[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?

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?

[R_J]

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)

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I suspect the pfc ic is not getting its VCC, (pin8) this is usually switched by a transistor (Qm803) maybe? The transistor should have a voltage on its collector and the emitter supplies the voltage to the pfc ic, The base is likely controled by a optocoupler and is turned on when PS_ON is high
ICM855s is a RT8296AH which might be the stepdown converter for the +5V standby

Here is the schematic for a BN44-00520C, it uses the same pfc ic and the circuit might be similar

I did locate QM803. Interestingly enough the OPTO's I think you are referring to also have unstable voltage on the cold side pins.

Transistor is a 2F. I'm going to get specs.

Posted.

Can you tell me for sure the right way to check this with a voltmeter, what setting and scale, and what I should expect if its good?

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I suspect the pfc ic is not getting its VCC, (pin8) this is usually switched by a transistor (Qm808) maybe? The transistor should have a voltage on its collector and the emitter supplies the voltage to the pfc ic, The base is likely controled by a optocoupler and is turned on when PS_ON is high
CM814 might be the VCC source for QM808
ICM855s is a RT8296AH which is a stepdown converter. it is likely for the A5V. You would need to trace its output pin to see where it goes.

Here is the schematic for a BN44-00520C, it uses the same pfc ic and the circuit might be similar

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Pfc circuit is ICP801S QP801s etc. So check the voltage on the main capacitor and see what the voltage does, it should be 160v in standby, then go to around 400v.
You could ground the BLU_ON pin to perevent the backlight circuit from turning on, but it does look like the backlight circuit is ok if you are getting 100 volts, remember that the backlight voltage will likely drop due to its own protection circuit.

SJ has a repair kit for this board, so have a look at it and check the parts that are included, like the fets and diodes. also if you can provide the numbers on ICP801s and ICM855s might help.

Main cap voltage constant at about 161v and makes no attempt to rise. I checked all the components in the PFC circuit around ICP801/QP801 and found nothing that appears amiss. I checked the readings against the same numbered components on another Samsung PSU (BN44-00775A) in the area of ICP801/QP801 and found similar readings between the components.

ICP801 is SPC7011F and is described as a power-factor correction converter IC operating in critical conduction mode.

I am unable to read the number on ICM855 so I posted a pic below to see if anyone can make it out by chance? Pic file names for this end in 962 and 566.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Pfc circuit is ICP801S QP801s etc. So check the voltage on the main capacitor and see what the voltage does, it should be 160v in standby, then go to around 400v.
You could ground the BLU_ON pin to perevent the backlight circuit from turning on, but it does look like the backlight circuit is ok if you are getting 100 volts, remember that the backlight voltage will likely drop due to its own protection circuit.

SJ has a repair kit for this board, so have a look at it and check the parts that are included, like the fets and diodes. also if you can provide the numbers on ICP801s and ICM855s might help.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

How do I identify the components in the PFC circuit? Is there a specific area on the PSU I need to be looking at?

Maybe I should also tell you I am getting an unstable 100 or so volts at the LED connector on the PSU? Does this help any ?

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

With PS_ON grounded, that forced the power supply into standby with the FE5760 operating in burst mode, like it should.
Without the PS_ON grounded, NOW the FE5760 is being told to run full on, ALSO the pfc circuit is being told to turn on.
So there could be a short in the pfc circut?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

"Is it really OK to ground the PS_on pin with the voltage being low and unstable?" Yes, that will stop the rest of the switched power supplies to come on so only the standby voltage will be present.

Ok here's my observations:

After plugging in the TV it takes a couple minutes for voltage to show up at the A5V terminal.

With the main board plugged in to the PSU voltage is unstable at A5V from 2-4volts or so.

With the main board unhooked from the PSU voltage becomes mostly stable and is about 4 volts.

When the main board is unhooked from the PSU and PS_on is grounded voltage on A5V comes up to 5.3v and is stable