LG 50PS3000 no picture

[axel.villamo]

Hi,

I have a LG 50PS3000 that is about 2.5 years old, that gave up on me the other day. When I pressed the start button (the main on the tv) it showed a bit of the old info on the screen that plasmas usally does and then it went completely black.

My fault tracing:
*The remote works since I can put it into standby/on from it.

*VS and VA from the power board gives ok values.

*Ysus board: VSC and VY are 0 but peaks to a higher value intermittent which could be normal value. My DMM is to slow to find the real peak. As this happens it Y-sus make noise (click) in the same time interval. I checked the mosfets onboard which gave messy values. I did desolder some of them and they appeared ok.

*Zsus-board: Vzb are constant 0. Nothing more is done.

*All caps looks ok.

Any inpus?

The sus boards are quite hard to find and expensive where i live so I would like to repair it. But before desolder everything on them I some input would be appreciated.


Ps. I could see this coming. When I bought it I was worried about the loud switch noise from the power electronics and I actually opened the TV and checked for vibration parts.

BR
Axel

[PlainBill]

Re: LG 50PS3000 no picture

The service manual is available at Elektrotanya. While you are there, try searching for LG Training Manual.

Pictures help us help you. For the first one, a single picture of the back of the TV (with the back cover removed), and one each of the power supply, Y-Sustain, and Z-sustain. Well lit, and clear are preferred, as close to (but not over) 2000 x 2000 pixels, please. Attach the pictures using 'Manage Attachments' - below the text entry area.

The fact that voltages are off is in itself informative. The standard approach is to disconnect the power cable from the Z-sustain, turn on the TV, and measure voltages at the power supply. Reconnect, disconnect the power cable from the Y-Sustain and repeat. And finally, measure the voltage with both power cables disconnected.

PlainBill

[axel.villamo]

Re: LG 50PS3000 no picture

Thanks for the fast reply.

I have read other threads in this forum and have downloaded the service manual and read though it. Based on that manual I started the diagnosis.

When everything is connected I get OK values from the powerboard.

Disconnection of Zsus board powercable only : powerboard ok values.

Disconnection of Ysus board powercable only: powerboard ok values.

Both Ysus and Zsus powercable dissconnected: Not ok values from powerboard. Very low values on VS, VA, and M5V.

[rayrod81]

Re: LG 50PS3000 no picture

Vsc and Vy are DC voltage and should not be fluctuating at all. Vzb at 0V also indicates a problem. Based on that information there is a problem on both sustain boards.

The fact that there are no voltages coming off the power supply when both boards are disconnected makes me believe that the power supply will not output the voltages if there are no loads connected. Many of the newer plasmas are designed this way.

A fluctuating Vsc and Vy indicate a bad mosfet, possibly more than one. Vzb at 0V indicates a shorted component on the Z-sus.

[axel.villamo]

Re: LG 50PS3000 no picture

Yes, accordingly the service manual a replacement of both boards would be the next step. Do you have any suggestion of fault tracing on the actual boards? Which components and how to test them.

Is it a possible scenario that both z and y board dies at the same time?

[axel.villamo]

Re: LG 50PS3000 no picture

I have some updates.

I found out that I I measured Vzb on Zsus wrong. I measured over the a resistor but it should be to ground.

When everything is connected I get 100 V on Vzb on zsus immediately when i plug in the power cord, which drops after connected (something like y=1-e^x, standard capacitance discharging). The VS to the board is always 195V which is normal. I interpret this as the board is working but is turned off? correct?

Vsc and Vy on Ysus does jumps a bit when I do the same operation. But it is more of a jitter.

I think that Ysus has blown (but all fuses are ok) or the controlboard.

[axel.villamo]

Re: LG 50PS3000 no picture

I have made some investigations of the ysus.

It seems that components (capasitors) next to the mosfets (marked 45F122) Q71 Q72 Q73 Q81 Q82 Q83 have fallen of
The same right next at the board tag, and a diode (D602).
If these components should be there and have fallen of the switching frequency
probably does not work as it should.

Unfourtunally I have not found the components (I have not dissabled everything yet either), but it would make sense that they fall off because this is probably the hottest place in the tv.

[rayrod81]

Re: LG 50PS3000 no picture

They are not missing just never there to begin with. You have a bad or shorted Mosfet, diode, or transistor. The easiest way to find them is to check resistance with a multimeter (not the diode checker mode). The bad component will have very low resistance or even a complete short.

[axel.villamo]

Re: LG 50PS3000 no picture

Latest operation on Ysus.
The mosfets and diodes connected to heatsinks were desoldered and a simple DMM check was performed (nothing found). I then resoldered them again and connected the board.
Now I get an intermittent flickering picture and Vzb on Zsus is ok. There comes a noise from the lower right transformer on Ysus with the same timing as the flickering picture.

When I measure IC902 and IC904 (read from a service manual) I do not get the values as expected and the tv shuts down (reboot of tv required) the other circuts seems ok.

Also the next top heatsink on top buffer card gets warm. I checked underneath it and it looked ok and the card measures ok.

[achristi]

Re: LG 50PS3000 no picture

Hi, I have a similar issue with my LG 50PS3000.
A few days ago I had a local power outage and afterwards the TV wouldn't come out of standby. After 1,5 days suddenly it did function again but any HDMI or SCART input results in "no signal" being displayed. Antenna and composite inputs do work allthough without sound. I suspect the main board to be faulty. Found it for €55 online locally so if someone can confirm I will try and replace it. This is the 3rd time I have issues with the set after a power outage, already installed an power protector but it doesn't seem to help. Any bright idea's?

Kind regards, Arnd

[tom66]

Re: LG 50PS3000 no picture

Power protectors/surge protectors rarely help, unfortunately, because none of them protect HDMI ports. It's just bad luck that you have to deal with, if it happens. Or get extended warranty but more than likely you won't ever claim back much of what you paid in.

Main board should fix it.

[achristi]

Re: LG 50PS3000 no picture

ok, txs for the confirmation tom66!