Lg 50pk750

[hpservertech]

Evening all.

Have an LG 50PK750 that turns on, has sound but no video. Previous owner tried to do a repair on the power supply board, but did a horrible job (burned through traces, unsoldered some smds as well) so I got a replacement. New board in and the same issue.

VA - 60
VS - 204

jumpered 51 & 52 on the main board and removed the p31 cable. No test patterns.

From searching it seems that most that have similar issue they do get test patterns which means the main board is bad, but I haven't found anything that helps me figure out what to do/test next if there are no test patterns.

Any help is appreciated.


Pictures:
https://photos.app.goo.gl/Uu4vDiKzDFwXZ6qV8
https://photos.app.goo.gl/5HLdacCPqetmvc9R6
https://photos.app.goo.gl/aqQF24WLHGM58ujQ8
https://photos.app.goo.gl/dret7X2ypgJZLPKF6
https://photos.app.goo.gl/A43DFqbB4gX6Sy7d8
https://photos.app.goo.gl/tCe1VrNCrqi18Eto6

[hpservertech]

Re: Lg 50pk750

Anyone have any thoughts?

[dick_barton]

Re: Lg 50pk750

On the back of screen panel there's a white label which gives varous voltages , about 6 of them.
5v, 60v, 203V etc (hard to read from picture). Have you measured them ALL and do they tie up with what is on that sticker?

[hpservertech]

Re: Lg 50pk750

yes. VA & VS & m5v all match the PS board and both sus boards.

[dick_barton]

Re: Lg 50pk750

There are a number of other voltages that can be measured. Can you post a picture of the label with the voltages given on it.
It's also more useful to have the pictures attached to your post rather than having to go backwards and forwards looking. You can attach them by using the Go Advanced button below when posting.

What is the flashing sequence / timing of D1 on the control board?

[hpservertech]

Re: Lg 50pk750

D1 is not flashing

Also on the power supply I checked the voltage for P813. I dont think these are correct readings. This is with the TV on.

Attached pictures

[dick_barton]

Re: Lg 50pk750

There are also a number of fuses on your Ysus board you could check are not open circuit and several voltage points to measure. Vsus and Yv

Photo courtsey of Shopjimmy

[hpservertech]

Re: Lg 50pk750

Went ahead and added the other pictures as well.

[hpservertech]

Re: Lg 50pk750

fuses all test good.
VS & VA match the sticker 60v & 203v

[dick_barton]

Re: Lg 50pk750

D1 is not flashing

Also on the power supply I checked the voltage for P813. I dont think these are correct readings. This is with the TV on.

Attached pictures

Those voltages are not correct. What are you using for ground ie where are you placing your black meter lead?

[hpservertech]

Re: Lg 50pk750

See what you are saying on sus board.
vsc - 0
vsy - fluctuates 32-33v
vs fs103 - 132v (should be 125v)
vs fs101 - 10v (should be 125v)

[hpservertech]

Re: Lg 50pk750

Chassis ground. also used the ground point on that connector, same voltages

[dick_barton]

Re: Lg 50pk750

Measure Vy across resistor the positive and negative ends are marked and place your meter probe across it to read the voltage. Likewise for Vy

[hpservertech]

Re: Lg 50pk750

I'm an idiot. Had the meter on ac. Updating voltages. The voltages are correct for the P813 connector. Sorry about all that.

Measured across resister
vsc - 192
vy - 151

measured from + side to ground
vs f103 - 60
vs f101 - 5

[dick_barton]

Re: Lg 50pk750

The Vsc and Vy look good.
The other two readings you show as vs f103 and vs f101 are fuses which you need to measure with the set powered down and disconnected from the power source. Then using your meter set to ohms measure across each fuse. There are 4 that I can make out on this board which I have marked with red arrows to points to them. They should measure 0 ohms or close to 0 ohms. I suspect they are all OK.

Other than that I'm puzzled. The D1 diode on the control board is definately not flashing. Is it lit at all.

I think you have a faultly control board but I would wait to see what more experienced members can suggest.

[hpservertech]

Re: Lg 50pk750

D1 is definately not flashing or lit up.

Get no test pattern with 51/52 jumpered and p31 disconnected.

Checked the ones you pointed out and they call came back at 0

[dick_barton]

Re: Lg 50pk750

Your voltages all look good. However there is no led flashing on the control board and unable to get into the test pattern when jumping points R51/52.

Perhaps someone else could advise on the probability of it being a faulty control board.

[hpservertech]

Re: Lg 50pk750

Dick got it right. It was the control board. $20 later and it's working. Thanks!