Samsung UH50EH5300FXZA, help with a transformer?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Opinions on transferring one from another board? I have several scrappers with this IC on them

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I took voltages at all the pins of the PFC IC. Here's what I came up with:


SOVP 5.Pin assignment

FB COMP RT OVP
1 2 3 4

8 7 6 5
VCC OUT GND IS


1 FB Feedback Voltage Input: 1.016v
2 COMP Compensation Output of error amplifier: shot up to .5v, dropped off slowly
3 RT Set Maximum on time: 0v
4 OVP Over voltage detection: .973v steady
5 IS Current Sense Input: 0
6 GND Ground
7 OUT Output: 0
8 VCC Power Supply: 11.95v

So if I'm seeing things right...zero volts at the output that drives the MOSFET= shorted MOSFET or bad PFC control IC?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

those two resistors resistors are connected in parallel.
http://kiloohm.info/smd4-resistor/5602
5602 = 56K
754 =750K
So total resistance will be <56K

BEP may be ferrite inductor so it will show like jumper. Look for other BEPxx on the board and check them.

LOL I was reading it upside down! I see it now.

There are no other items marked BEP near in the PFC IC area?

With all resistors and items near the PFC IC checking OK are we thinking bad PFC IC? Should I now take pinout readings on the PFC IC?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

those two resistors resistors are connected in parallel.
http://kiloohm.info/smd4-resistor/5602
5602 = 56K
754 =750K
So total resistance will be <56K

BEP may be ferrite inductor so it will show like jumper. Look for other BEPxx on the board and check them.

[DXseekerMO]

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.

That tells me the pfc circuit is not running, The pfc circuit in the schematic I provided should be very similar, the only difference is your board only has one pfc fet.
Check the resistors around the ic, There are two resistor strings going to pin 1 & 4, give them a check, they are high resistance values. The schematic shows a 47Ω off pin 5 to a pair of resistors to ground, I can't make out that circuit on you board but check any resistors there, Then check the gate resistors between pin 7 and the fet's gate (10Ω)
It could be that the ic itself is bad
The ic's VCC is normally 12 volts and the ic will shut down at 9v
Post the pin number and voltage on each pin, carefully not to short a pin, Best way is to follow the trace from the pin to another component and measure the voltage there

OK I think I found something significant:

Two resistors RP819 and RP818 that should be 20.9Mohms and 750Kohms both check at 50,900ohms. I'm guessing these are actually open and the resistance I'm getting is from other surrounding components.

I also found BEP801 that shows zero resistance. I can't make out the numbering on top but it kinda reminds me of a jumper?

Should I replace these before testing pin voltage?

From pin 7 to the gate there is 100ohms resistance

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Post 43

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

I cannot see why the readings now are so much different than what you have shown above.
Now yo have Voltage to run the PFC IC.

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

That tells me the pfc circuit is not running, The pfc circuit in the schematic I provided should be very similar, the only difference is your board only has one pfc fet.
Check the resistors around the ic, There are two resistor strings going to pin 1 & 4, give them a check, they are high resistance values. The schematic shows a 47Ω off pin 5 to a pair of resistors to ground, I can't make out that circuit on you board but check any resistors there, Then check the gate resistors between pin 7 and the fet's gate (10Ω)
It could be that the ic itself is bad
The ic's VCC is normally 12 volts and the ic will shut down at 9v
Post the pin number and voltage on each pin, carefully not to short a pin, Best way is to follow the trace from the pin to another component and measure the voltage there

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Ok, so icp801s (pfc ic) is getting VCC, did the voltage across the main Cap. CP806S change from 160v and increase?

Top reading from across the main cap was 164.1v with PS_on not grounded

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Ok, so icp801s (pfc ic) is getting VCC, did the voltage across the main Cap. CP806S change from 160v and increase?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Check that DP801CS diode (on back side of board) and DP803 & DP805 diodes on top side are not shorted.
Then if you can measure the voltage across CM809 and CM814 (in standby PS_ON grounded)
Then unground PS_ON and see what the voltages do, and also check for the voltage on pin 8 of the pfc ic.

The diodes you mentioned have a good diode reading on all.

Across CM809.....PS_on grounded 11.12v, PS_on not grounded 10.13 - 10.17v

Across CM814.....PS_on grounded 10.21v, PS_on not grounded 10.89 - 11.10v

At pin8 of ICP801S there is a pretty constant 10.91 to 10.95v, PS_on ungrounded

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Check that DP801CS diode (on back side of board) and DP803 & DP805 diodes on top side are not shorted.
Then if you can measure the voltage across CM809 and CM814 (in standby PS_ON grounded)
Then unground PS_ON and see what the voltages do, and also check for the voltage on pin 8 of the pfc ic.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

So there must be a different part of the PFC circuit that needs attention. The fact is when PS_on isn't grounded it looks like the PSU is trying to start but the main cap voltage always remains about 161v.

Should I un-ground PS_on now and try to locate the source of the up-and-down voltage, or are we still troubleshooting in another fashion?

[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.

[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?

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?

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?

[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?

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.

[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.

[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?