OLED65CX5LB PSU Feedback Loop Issues

[CiorapulUcigas]

Hey guys. I have the dreaded OLED65CX5LB that LG decided to make REV 2.0 of the PSU 5 months after the first rev. If they moved that quickly you know that there is a problem ha ha.
My TV still has REV1.0 and has died. I have managed to get it back to life and it is working almost faultless.

The TV turns on if I press the power button 4-5 times. Once it's on it works perfectly and no reset clicking can be heard.
While on Stand-by I can hear the resets clicking, so I decided to investigate.

Well I am a bit stuck and need some help

The IC that controls the primary side of the transformer is SSC3S927L

Measuring the pins against the datasheet I got:
VCC 16V
FB 0.08V
REG 8V
VB 0-60V
VS 6-23V
VGS 6-60V
ST 370V

This bad boy needs FB voltage to be at min 0.3V.

Mine was 0.08 and REG was 8V (has to be 9V min)

The optocoupler seems to be working and voltage is fluctuating


On the secondary side I have measured almost every single part and can't find anything obvious.

20VS is about 15V
12VM is about 8.5V

I have removed the filtering caps from 12VM (3 of them) and the clicking seems to be gone but my 2.5V ref is sometimes down to 2V and also my FB voltage is touching 0.3V so I guess that’s what’s stopping the resets.

With the clicking stopped REG is above 9V.

So somewhere in this Feedback Loop I have a problem, please help as I am losing my mind.

Thank you.

[Diah]

first of all this had nothings to do with REV 1 or 2

you wrote
20VS is about 15V
12VM is about 8.5V

12VM will be at this stage as STBY on the cold area because Hot area SPMS didn't switched high,, when it goes high after MB send Power_on the VM will reach 12Vthe first things i do suggust send IN_STOP command to the TV via IR siy or apk android or service RC

[CiorapulUcigas]

I think they were doing free PSU replacements from Rev 1 to 2 in the US. I might be wrong.

[Diah]

I think they were doing free PSU replacements from Rev 1 to 2 in the US. I might be wrong.

and why in US LOL as they give them only 1 years guaranties.. here in EU we have 3 years... so they should care of our complain not the US

[CiorapulUcigas]

Yeah you are right, we do have some customers rights compared to the US.

Can I ask what benefits do I get from doing a factory reset? The psu is missing FB voltage with or without the Mainboard connected.

And you are probably right about 12VM, once the TV turns on the clicking disappears and TV works with no issues.

So I think the problem is on the Feedback loop for standby voltage.

[Davi.p]

Hi, the case appears almost simple, replace the shunt regulator TL431 relative to the stby section or smd similar and stop.. but this is not a design flaw, this is a common house mains spike

[Diah]

Yeah you are right, we do have some customers rights compared to the US.

Can I ask what benefits do I get from doing a factory reset? The psu is missing FB voltage with or without the Mainboard connected.

And you are probably right about 12VM, once the TV turns on the clicking disappears and TV works with no issues.

So I think the problem is on the Feedback loop for standby voltage.

during long period of time using the TV. its collect allot of rubbish TEMP., especial when the set connected to internet. same way to mobile which it need one per week restart to avoid hacker and this unwanted TEMP.
IN_STOP command will clean the set to factory state.

[Diah]

dont play with hot area or relay.. this is wrong talking... follow on the socket at cold area oins power_on.. its goes to circuit 2 transistor with one small transformer and 2 caps... some time on of the caps get leek so it will not pass the power on signal via opto. to switch the relay on

[CiorapulUcigas]

Hi, the case appears almost simple, replace the shunt regulator TL431 relative to the stby section or smd similar and stop.. but this is not a design flaw, this is a common house mains spike

I understand, I work in electronics manufacturing, and when we up issue a design it’s because of a problem or a bom change(unavailable parts, etc.)

The shunt regulator is KIA431BCM and will do some measurements on it later and compare with datasheet.

Also when the power supply is in tv and everything connected, if I press power on the remote a couple of times the reset clicks go away and after that the next power button press will turn on the tv and everything will work just fine.

[Davi.p]

sorry i don't understand, are you an electronics engineer? So you are far from my knowledge, anyway i try to help.... the mention of voltage outputs lower of many volts is typical sign of bad FB especially the said component, but i read again the 1st post and i noticed some flaws, the ic voltages are somehow low and you pointed it also, especially the ST, sorry i don't get the datasheet now but it is i guess the start current input pin, it is at 370 when usually PFC is 390/400v, i suppose this is the type new style where the PFC is active in standby, i faced the same in a Panasonic, so stby voltage is too low to make it start correctly or are so the regular voltages, due to attempts some components heats a bit, resistance rises very few enough to change the FB so the output V..

[CiorapulUcigas]

Because I work on the Manufacturing side of electronics I almost never get to use my skills. We always build what the customer wants so I am not an experienced electronics engineer, I studied electronics in school but I am a process engineer now.

Yes FB voltage is not good when the psu is clicking. When it stops clicking is at min value 0.3V

I have 2.5V at vref on KIA431BCM and cathode is 1.9-3V unstable.

Disregard resistors in red, haven’t managed to measure them out of circuit yet. Everything in green has been measured and is good.

I suspect the capacitor on the cathode of the shunt regulator atm.

Thank you for your help, I appreciate it.

[Davi.p]

No, maybe you don't understand me, my second post i suspected no more feedback but bad PFC, what is bad on PFC must you discover, maybe a faulty diode in diode bridge (half wave out) , bad straightforward diode, shorted winding in power inductance..

[CiorapulUcigas]

Okay, thank you, will move my focus on finding out what is wrong on hot side.
ST voltage at SSC3S927L is 360v or 370v

[CiorapulUcigas]

Rectifier bridge is at 500v
Big caps are rated at 460V and measuring 500v

St pin is at 360v

Investigating

[Davi.p]

Measuring errors.. warning.. if primary would be much higher then secondary would follow the same..

[Diah]

Man... this is my last post over here ......dont play with hot area.... its fine and you have 12VM t 8.5V this standby V.

[CiorapulUcigas]

Man... this is my last post over here ......dont play with hot area.... its fine and you have 12VM t 8.5V this standby V.

I understand, don’t leave, I am just testing stuff for a better understanding.

Do you think ST pin at 360v is okay?

I have measured VSEN pin:
-clicking is 2.9V
-no click is 2.4-2.7V

So based on the Datasheet of this IC those voltages are correlated with: AC Line Detection

[Diah]

I understand, don't leave, I am just testing stuff for a better understanding.

Do you think ST pin at 360v is okay?

I have measured VSEN pin:
-clicking is 2.9V
-no click is 2.4-2.7V

So based on the Datasheet of this IC those voltages are correlated with: AC Line Detection

testing on hot area are risky when it work.. and no need
360V fine because yours TV should be in active SPMS... because when its at standby it need for refresh pixel

disconnect the MB... and took from the VM 8.5V stepdown circuit 3.3V fed power on... you will hear the click and VM goes to 12.. and if you fed this 3.3V to t-con_on you will have 12V T-con vcc and VDD >20V to T-con driver of OLED.

[Davi.p]

what's the model code of power board?

[CiorapulUcigas]

PCB:EAX69061002(1.0)

P/N:EAY65689423