Samsung UH50EH5300FXZA, help with a transformer?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Is there a solder pad on the bottom of FE5760? I can't read Japanese so I can't tell by the datasheet.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I don't think so, Why? If the ic was bad I don't think you would be getting any voltage at all on the 5VA standby, Did you check the parts on the gate of the shorted fet?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I don't think so, Why? If the ic was bad I don't think you would be getting any voltage at all on the 5VA standby, Did you check the parts on the gate of the shorted fet?

Checked, here's what I found:

CM803 has about 16Kohms in one direction and open in the other. I didn't see a bulge on the case anywhere.

All items off the gates of QM801CS and QM802CS appear to be of the appropriate resistance and not shorted, save for resistance across CM810 which seems low at 101ohms?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

How about the capacitance of that coupling/DC blocking cap CM803s?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

How about the capacitance of that coupling/DC blocking cap CM803s?

I'll have to get it off of the board and check it. Do you know what the prescribed capacitance is for that cap? 0.027uF?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

0.027uF 5% Polypropylene type. It is commonly failed cap in that section of the circuit.
SIC cap looks like 598B series.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

That FA5760N will be operating in burst mode (standby) so the only voltage that should be close would be the A5V, the voltage off the transformer will be low likely around 8 volts

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

0.027uF 5% Polypropylene type. It is commonly failed cap in that section of the circuit.
SIC cap looks like 598B series.

Capacitance checks at 0.0264uF

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

OK, that is good. The circuit is switching but it is not switching right.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

It's ok, So what is the voltage you get on CM853, you might want to check Cm809 and Cm814
In standby the voltage on CM853 could be around 8 volts

I was just thinking that without the main connected, the power supply might be trying to turn itself on due to pull up resistors on the PS_ON pin. You could ground the PS_ON pin and see if A5V is stable

I see you have 160v on the main filter so the pfc is off at this time

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

OK, that is good. The circuit is switching but it is not switching right.

It's ok, So what is the voltage you get on CM853, you might want to check Cm809 and Cm814
In standby the voltage on CM853 could be around 8 volts

I was just thinking that without the main connected, the power supply might be trying to turn itself on due to pull up resistors on the PS_ON pin. You could ground the PS_ON pin and see if A5V is stable

I see you have 160v on the main filter so the pfc is off at this time

Caps CM809 and CM814 have proper capacitance out of circuit.

On CM853 there is 3.5 to 4.2 volts, alternating from lower to higher about every couple seconds. The rhythmic fashion of the voltage change reminds me of something trying to start.

Is it really OK to ground the PS_on pin with the voltage being low and unstable?

[budm]

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.

[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

[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?

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?

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?

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?

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?

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 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)