Samsung UH50EH5300FXZA, help with a transformer?

[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?

[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?

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?

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?

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?

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

[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.

[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?

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?

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?

[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?

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

[R_J]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

i would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
taking an ic from another board should be fine

+1

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Thanks R_J and budm, I will re-check the gate-related items off that FET and if all is good I will install the IC and report when finished.

Is this IC glued to the board? Any suggestions to deal with that if it is?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Well sodded dog, I ripped several traces on the board right by that IC. The zener in-circuit did not show short...kind of a moot point now tho.

This is because I still don't have a hot air station. Speaking of, does anyone have an opinion about this one?

https://www.ebay.com/itm/X-Tronic-Mo...MAi:rk:17:pf:0

[DXseekerMO]

Update:

I would suspect bad ic, a shorted mos fet would likely blow something, but check the parts in the gate circuit, there might be a zener to ground that is shorted
Taking an ic from another board should be fine

+1

Well today the replacement PSU came in. Seller claimed it was from a new cracked screen TV and worked. When I got it the ground pads were nice and clean so I believe the sellers claim. I put it in the TV and no happy, TV dead. I checked the main cap voltage and found nothing. A further look and the reason showed up....the main fuse was cut out and missing.

Fast forward an hour: Ebay seller refunded my money with no messages, just a refund. I checked for a short in the mains on the board and found nothing, then checked all the FETs and Diodes, all indicated good. I installed the fuse from my old PSU, installed the PSU in the TV.....then lo and behold, the TV turned on and everything worked!

Fast forward another 30min. Everything was looking good, TV channels tuned and functions appeared to be working. I was using smart hub and tried getting in to the youtube app but it said it failed to connect due to network interference then later said it needed updating. I tried to use apps during this time but the little spinning circle with "updating" next to it wouldn't let me. Next thing I know the TV shuts off then starts boot-looping, eventually with no backlights or logo.

I'm letting it cool off to see if it will later turn on and stay on. At that point I intend to re-set smart hub then do a master reset on the TV and try again. So either I interrupted the update and bricked the TV....or perhaps we have an EEPROM or BGA soldering failure.

The good news: The display panel is very good in this TV, no lines or other things I feared fixing a model known for panel issues. I just have the boot loop and that appears to be it.

If it continues to boot loop, aren't there test points near the main EEPROM that can be shorted to re-set the EEPROM itself?

EDIT:ADD: Tried unhooking the power button and WIFI module right after turning it on and the problem still exist.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Updated voltage readings:

1 B13V.......12.47v, drops to 0 and comes back up to 12.47v
2 P_dim......2.0v when backlights are on, otherwise 0-.7v when boot looping
3 B13V.......Same as 1
4 B13V.......Same as 1
5 Vamp......12.47v drops to 0 and comes back up to 12.47v
6 BLU_on....4.79v when backlights are on, otherwise 0-..13v when boot looping
7 Vamp......12.47v
8, 9, 10......GND
11 B5V.......5.24v drops to 0 and comes back up to 5.24
12 A5V.......5.25 constant
13 B5V.......Same as 11
14 PS_on....3.29v, drops to .2v, comes back up to 3.29v

Furthermore I took voltage readings at the backlight connector, attached and unhooked from the PSU:

1 NC
2 D+..........347v, drops to 220v, returns to 347v......unhooked 347v
3 S1- .........297v, drops to 176v, returns to 297v......unhooked 0v
4 S2+ ........297v, drops to 176v, returns to 297v......unhooked 0v
5 NC
6 S2- .........306v, drops to 176v, returns to 306v......unhooked 0v
7 S3+.........306v, drops to 176v, returns to 306v......unhooked 0v
8 D- ...........316v, drops to 208v, returns to 316v.....unhooked 316v
9 NC

EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:

1 NC
2 D+.........264
3 S1- ........159
4 S2+ .......159
5 NC
6 S2- ........107
7 S3+........107
8 D- ..........55
9 NC

Voltage difference between D+ and S1- = 104v
Voltage difference between S2+ and S2- = 52v
Voltage difference between S3+ and D- = 52v
D+ and S1- run two pair of strings. 104/2 = 52

Based on the voltages found the power supply and backlight strings cannot be the problem, leaving the main, T-CON and connections/panel responsible.

So it looks like all the necessary voltages are available when the main board asks for them, but some of the time the main board isn't sending some command voltages back to the PSU?

The paragraph that was here is redacted

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

1) What is the P/N of LED driver IC9151 8-pin SMD?
2) Lift up one leg of diode D8151C and check the RESISTANCE betweent he two legs in both directions.

"EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:" So the backlights are still not on?
If you look at the LED Voltage chart, it shows 229v @ 470mA with load, you are getting 264V so it means it is not seeing the full load.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

1) What is the P/N of LED driver IC9151 8-pin SMD?
2) Lift up one leg of diode D8151C and check the RESISTANCE betweent he two legs in both directions.

"EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:" So the backlights are still not on?
If you look at the LED Voltage chart, it shows 229v @ 470mA with load, you are getting 264V so it means it is not seeing the full load.

When I unhook the main board from the PSU the backlights are on, this post was updated 5min ago

EDIT/ADD: I unhooked the main board from the PSU and took voltage readings on the backlight connector:

1 NC
2 D+.........264
3 S1- ........159
4 S2+ .......159
5 NC
6 S2- ........107
7 S3+........107
8 D- ..........55
9 NC

Voltage difference between D+ and S1- = 104v
Voltage difference between S2+ and S2- = 52v
Voltage difference between S3+ and D- = 52v
D+ and S1- run two pair of strings. 104/2 = 52