Lg 50pk750 help!!!!

[LGinMD]

Hello all!

Just wanted to start off by saying I love this site and look forward to enjoying many posts to come...

Now, I have a LG 50" 50pk750 that will power up and stay powered up... The backlight comes on and the screen gets lighter but once the front led turns blue about 10secs later nothing happens... None of the front panel buttons do anything. Channel - +, Vol - +, Input, Menu... all do nothing. If I unplug the top Ysus buffer the top of the screen has static but no sound. If I unplug the lower Ysus buffer theres static on the lower and no sound. I get an 11 from the Control board LED which I havent the slightest as to what it means....

Any and all help is appreciated!

Thanks!

[Hamie]

Re: Lg 50pk750 help!!!!

An 11 on the control board?
No idea what that means, the blinking led on the control board on an LG doesn't reveal any fault code.

you can generate test patterns on this tv by connecting the 2 holes beside R51 and R52 on the control board. Make sure you disconnect the lvds cable.

[LGinMD]

Re: Lg 50pk750 help!!!!

Make sure you disconnect the lvds cable.

Will try that today... When you say the LVDs cable, what are you referring too?

Also, if after connecting the two together nothing happens should I assume its the panel and not the YSUS board/ Buffers?

Thanks!

[ReeceyBurger123]

Re: Lg 50pk750 help!!!!

What exactly is the failure ? Tv becomes unresponsive ? If you unplug one of the Ybuffers only half the screen will work. Im confused can you please rephrase this. Cheers.

[LGinMD]

Re: Lg 50pk750 help!!!!

I can post a video of it if need be... Ill try to list in order of what happens/what Ive done.

1. Plugged in TV (Get Red LED on front).
2. Push power on the touch panel.
3. LED goes from Red to Blue (Relays Click)
4. Screen turns an off greyish color (Backlight working?)
5. Blue LED turns off but TV remains on (No image on screen or sound)
6. After 10-15secs I can touch the different buttons on the touchpad (Input, Menu, Chan - +, Vol - +) and nothing happens but every time I push a button the led blinks as it sensing Im touching it..

7. If I unplug the upper buffer from the YSUS board the upper part of the screen is black with speckles and the lower is still grayish..
8. If I unplug the lower buffer from the YSUS board the lower part of the screen is black with speckles and the upper is still grayish...

Ive measured VS, VA, -VY, VSC, and VBR all of which are in range...

[ReeceyBurger123]

Re: Lg 50pk750 help!!!!

Ok alright thanks. Sounds like the Sustain boards are working which is why you are seeing "backlight" which is actually the pixels being primed up by the sustain boards. However it sounds like you either have a Mainboard or control board failure here. Can you upload pictures of the tv please.

[LGinMD]

Re: Lg 50pk750 help!!!!

What is it youd like to see?

Now the backlight doesnt stay bright for long... Say maybe 5 secs during startup then it dims to a faint grayish. It doesnt go black, the only time itll go black or "Off" is when the unit is switched off...

The previous owner stated that the screen would dim sometimes while watching it then go back to normal. He also said that on occasion it would go black...

[ReeceyBurger123]

Re: Lg 50pk750 help!!!!

Thats normal behavior, the screen starts the Pixels brighter. This is called priming this when the sustain boards ramp up voltage goes high to get the gases in the pixels ready to emit light. This priming process on Lg's lasts ablut 5 seconds then the sustain boards will lower and the tv should operate normally. Do you even see anything displayed on the screen ?

Pictures of the boards.

[LGinMD]

Re: Lg 50pk750 help!!!!

[LGinMD]

Re: Lg 50pk750 help!!!!

Nothing on the screen... Again, regardless of what button I push on the front panel the screen remains the same (Nothing)..

[ReeceyBurger123]

Re: Lg 50pk750 help!!!!

Ok is there a flashing Led on the Control board ?

[LGinMD]

Re: Lg 50pk750 help!!!!

Yes, I stated that in my initial post... It flashes 1 long then 1 short (11)

[ReeceyBurger123]

Re: Lg 50pk750 help!!!!

Alright ok sounding more and more like a Mainboard fault. Do what Hamie said and see if test patterns work.

[LGinMD]

Re: Lg 50pk750 help!!!!

Will do, not to sound stupid but which cable is the LVDS cable?

Also, given the two scenarios if the test patterns work then whats next?

If the test patters dont work then whats next?

[Hamie]

Re: Lg 50pk750 help!!!!

Just to clarify for test Patterns.

On the control board disconnect the LVDS cable. This cable is labelled P31.
The 2 holes you need to connect together with a paper clip or bit off wire are close to P31 beside the 2 resistors marked R51 and R52.

If you get test patterns you have a faulty mainboard.
Unfortunately the board is usually quite expensive as it in high demand.

[LGinMD]

Re: Lg 50pk750 help!!!!

Never mind I got it, P704 cable is the LVDS cable.. Just remove that cable and test by jumping the two stated earlier?

EDIT: Just saw your post Hamie, thanks!

[LGinMD]

Re: Lg 50pk750 help!!!!

Ok removed the LVDS cable and jumped the R51/52 holes and nothing happened. With the cable disconnected the LED on the front panel doesnt even light up.

[Hamie]

Re: Lg 50pk750 help!!!!

Can you post a picture of what you've done.

[LGinMD]

Re: Lg 50pk750 help!!!!

Can you post a picture of what you've done.

Never mind Hamie,

Im an idiot and unplugged the wrong cable... Luckily the unit didnt power up when I jumped the two lol...

UPDATE:

After jumping the R51/52 together while P31 was unplugged I DID GET THE TEST PATTERNS! Looks like im sourcing a MAINBOARD!

[LGinMD]

Re: Lg 50pk750 help!!!!

Only question is, which one is the "Main Board"? Its the board with all of the inputs on it correct? If not then I take it its the board in the center that has P31 on it?

Thanks again all!