LG 50pb690V Doesn't Turn on!

[reessi]

Re: LG 50pb690V Doesn't Turn on!

Well the board arrived and seams to be fine, but now I have other problems! I tested the board like the other one and didn't find any shorts and now with it in the set the VA VS voltages are back, in fact all voltages seam to be working not.

The problem now is upon turning it on from the mains the screen pulses on and off. When I say on it shows only black, as black looks on a tv, you know because its not true black! At the same time as the screen turns on the YSUS lets out a squeal noise which I couldn't pin point to an exact component!

So I've checked for obvious shorts on the YSUS - Caps, diodes etc, some transistors, couldn't find anything.

I then checked some surface mount caps on the little control board and half the caps measure 30 ohms, is that a definite short somewhere. Could this make the YSUS squeal?

Anyone know what could cause that noise! It is quite loud almost like a speaker is there!

Also dis-connecting the cable from the small control board to the YSUS stops the set from doing anything!

Also the power led only comes on after dis-connecting the mains.

Many thanks!

[reessi]

Re: LG 50pb690V Doesn't Turn on!

Also shorting the test pattern pins and dis-connecting the LVDS cable from the control board as sugggested by someone else does not have any affect on anything. It still pulses.

Also just tested again now after putting the control board back in from yesterday and the squeal is barley audible, you have to listen for it now. And the black is more like a light grey, I think it was like that all along I just didn't look at the front properly.

Cheers.

Cheers.

[reessi]

Re: LG 50pb690V Doesn't Turn on!

Anybody still looking?

[dick_barton]

Re: LG 50pb690V Doesn't Turn on!

There should be a label on the panel similar to the one attached. Do the voltages that you read match up with what is printed on the label of your panel.

[reessi]

Re: LG 50pb690V Doesn't Turn on!

All voltages on the boards read correctly. Ths VS states 205 and is at 200, I thought that was within tolerance?

Cheers.

[reessi]

Re: LG 50pb690V Doesn't Turn on!

The VA states 55 and is at that. All PSU ones are correct.

[dick_barton]

Re: LG 50pb690V Doesn't Turn on!

I believe that if you have some screen brightness even if it's dim then the Zsus is working.

It would also be worth your while checking that you do not have a Ybuffer fault. There are plenty of Youtube video's to show you how to test.

What was the labelled and measured voltage for the following?
Label Voltage..........Measured Voltage
Vsc
-VY

[reessi]

Re: LG 50pb690V Doesn't Turn on!

I finally had time to look at this again. With all plugged then the screen flashes grey and the ZSUS ticks in time. No led on control board.

Removing screen tabs from ZSUS and TV boot with picture but very dark as no ZSUS connection. LED flashes on control board.

Does this say its def ZSUS. This is actually a replacement from the last time I tried to fix.

The previous one had many shorts and the TV did nothing.

It clearly lights the screen but then shuts off presumably detecting a fault.

Couldn't find any shorts.

How can test the parts properly. There is a line of sf20d300hpi transistors on a heatsink but no shorts and some other different ones surface mounted.

Any suggestions or could there be a fault on another board causing it to stop?

Cheers.

[reessi]

Re: LG 50pb690V Doesn't Turn on!

Also all PSU voltages measure correct including the VS and VA.

Cheers.

[reessi]

Re: LG 50pb690V Doesn't Turn on!

I started a new thread for the new problem with the replacement ZSUS board as this thread is really old. Original ZSUS had shorted transistors stopping TV powering up. Can be determined by checking VS & VA voltages. They were missing dues to shorts on ZSUS board.

Thanks.