LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

[Beau28713]

Any body have a service manual or schematics for a LG 50PN4500? I have a service manual but it only list the main board with its schematics. I'm particularly interested in the Y-sus board (EAX64561401)

[tvtimmy]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

Watch these two videos.

It is based on real life experience as documented and in our YouTube videos "CWgdAKTZHSo" and "W4nEv07vpmU", to which we regretfully are not allowed to provide links, so you can see them by simply searching for the unique identifiers.
Copy and paste the text in the parentheses " ".

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

I watched those videos and bought the repair kit. Which in turn corrected the main issues (Blown fets) on my Y-Sus board.

But now my issue is I have no health light on my control board and I only have sound with no video output. I have all correct voltage outputs (205V,55V,17v,12v,5v,) Except I don't have the 18v at the output pin on my Y-SUS board. My M_on (Monitor on) signal from the main board is there and it is thus activating the M5v (5V) signal on my PS which then is going to my Y-SUS board which is used for the 18V regulation output from the Y-SUS to the control board and the Z-SUS. The control board needs the 18v to generate the 3.3V it uses to function. Thus is is why I believe I don't have my health light or any activity on my control board. Most of the ICs are not labeled with part numbers I can use to look up and see as to which IC and section on the Y-SUS board is supposed to be generating the 18V. I was hoping to find a schematic that listed the parts with pinouts.

[tom66]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

LG doesn't publish schematics of their Y and Z sustain boards, sorry.
Post a picture of your boards and we may be able to help.

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

Okay So I was able to trace out the Y-SUS circuit and I found the 18V regulator (IC205 AS78XXA) that is used for the 18v output at pin 6 of the Y-sus board. The regulator input is only 3.6v and that is why I don't have my 18v and I only have 3.2v at the 18v pin on the Y-SUS board. I will trace out the input to the regulator tomorrow and see why I only have 3.6v input.

[Biruslapio]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

I've repaired two of these boards,on both of them one of these white(500V) SMD capacitors failed and shorted,destroying a SMK0460 or the 30F131 and 30F123 in the process.
You can test this 18V regulator off the board,at the datasheet it has a test circuit,but since it's input is low something else may be the culprit.

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

I have found and replaced all the blown FETS and C417 and 418. Now i'm in the process of repairing the 18v circuit. The regulator is working fine its just not getting the proper input. So I will be troubleshooting that tomorrow.

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

Still troubleshooting. Having some fluctuating readings at the IC's VCC and regulator inputs. I don't have my 5VF nor do i have my 15VF from the regulators. The regulators seam to work properly. But my PWM Current-Mode Controller (IC 201) VCC input goes up and down from from 6v all the way up to 13v and All my regulator's (IC631 5Vf and IC204 15Vf) input voltages go up and down from 1v to 3v. Gota find out as to why the circuits are doing this.

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

Anyway I can change the title to this thread so more people will look and maybe throw out some suggestions?

[Biruslapio]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

A mod may help you with the title.
I would start measuring the resistors since that is simple and quick to get out of the way.
Have you followed the PCB trace from the VCC of the 18V regulator? The controllers VCC fluctuate,what if you take them off the board?

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

Yes sir, This morning I stated reverse engineering and tracing out all the regulator circuits 5v, 15v, and 18v. When i get it all straightened out i will post it here for others to use. I'm going to remove some sketchy components tomorrow and see what effect it will have on the circuit. There is a lot of fluctuation in the voltage for all the reg inputs and IC's Vcc. Something is making go up and down and not staying steady.

[Beau28713]

Re: LG 50PN4500 service manual with ZYX-SUS board Schematics needed

tvtimmy here is the pic you wanted sir

[tom66]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

I have edited the thread title, hope it's more appropriate
Sorry I don't have any thoughts right now.

[R_J]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

Whats the number on ic201? The ic's usually have a startup cell to produce the initial VCC and then a secondary winding from the transformer supplies the voltage to keep it running, usually about 18-20 volts.
Does the ouput of the ic drive a fet?
I also see there are a couple other voltages that may come from that same transformer and looks like one of them might supply the buffer ic's (caps and diodes [D202 etc.] in corner of board)
One of the lines seems to feed D641 to D644

[tvtimmy]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

He needs to know how to test the ic chips on the ysus. I thought it might be like a Samsung board but its not.

[Beau28713]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

Whats the number on ic201? The ic's usually have a startup cell to produce the initial VCC and then a secondary winding from the transformer supplies the voltage to keep it running, usually about 18-20 volts.
Does the ouput of the ic drive a fet?
I also see there are a couple other voltages that may come from that same transformer and looks like one of them might supply the buffer ic's (caps and diodes [D202 etc.] in corner of board)
One of the lines seems to feed D641 to D644

IC201 (200d6) is PWM current-Mode controller that has an internal Voltage regulator that gets its regulator input voltage from the high voltage from the VS line via 47k 1 watt resistor. It is driving the fet that pulses the transformer that feeds the input voltages for the 15v and 18v regulators. Now what I did was remove IC201 from the circuit and injected a dc voltage via the 15v and 18v regulator input caps. Everything seamed to be working like it should. I had my 15v and 18v on the board at the regulator outputs, board test points and 18v pin on the p131 connector. Now granted i did not have the tv powered up because I was afraid I would blow something with my high voltage not being connected to the circuit. IC201 VCC pin voltage was fluctuating rapidly up and down from 6v to 11v and I think this is why my output voltage on my transformer was fluctuating up and down and that was what was also making my regulator voltages fluctuate up and down at a very low voltage. I think IC201 was never really coming on long enough to do anything. I think I may have a faulty controller. I'm still learning so if i'm on the wrong track please let me know. I can order a new controller for about $1.50.

[Beau28713]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

I have edited the thread title, hope it's more appropriate
Sorry I don't have any thoughts right now.

Thank you

[Beau28713]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

Tv is up and running.
Initial fault was sound but no picture.
A. 4 faulty fet transistors (Q401,Q402, Q403,Q404)
B. Two blown caps (C417 and C418)
After replacing these I discovered I had no 15v, 5v or 18v rails on my y-sus board and no power to my control board. (Fluctuations in voltages at the regulator inputs 1.8v-3.6v)
A. This was caused by a faulty Pwm fet driver ( ic201).

[Biruslapio]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

Cool fix, 2.2 OHMs resistor also replaced?
Careful so they do not touch the back cover metal.

[Beau28713]

Re: LG 50PN4500 - fluctuating Vcc/18V supply on Y-sustain board causing fault

I temp installed the 5 watt resistors so i could test the circuit until my new 1 watt 2.2 ohm batch comes in. The 5 watt ones will be removed before final assembly.