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...

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...

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...

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?

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 M5...

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...