LG 42LG3000 Strange fault will not go into standby!

[cheeky2]

I have this LG 42LG3000 Tv which operates on all inputs without any issues whatsoever. However when you try to turn the Tv off the screen goes blank as it would normally however it then turns itself back on again!
So far I have replaced the main board without any resolution to the problem.
When the inverters master and slave VIT71053.54 VIT71053.55 are disconnected from the power supply then the TV will turn off as it should (obviously without any ccfl output).
I have read through a few posts for this model without anyone having this issue as far as I can tell.
I either suspect the power supply or the inverters however as the inverters work properly I am pulling my hair out at the moment trying to work out what is causing the issues.
I had a set of good ccfl 42inch tubes which I thought might be causing a lamp error however exactly the same fault with them.
If I just unplug the master inverter the TV will go into standby and out of standby no issues.
The 24V to the inverter is good to the inverter.
The inverter on /off is 5V when on
PWM-DIM is 3.3V when on
Error is 0V when on or off
I am leaning towards a psu issue however any help or thoughts would be welcome Thanks

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

Also removed the side control buttons to ensure they were not affecting operation somehow. Used another remote control to ensure it wasn't sending out the wrong codes.
I am now going to try disconnecting each of the control pins from the inverter master to see if I can isolate what is preventing standby operation on the TV.
This will hopefully point me in the direction of the fault location.

[ducky29]

Re: LG 42LG3000 Strange fault will not go into standby!

Try on hdmi. The fault should not happen if your tv is on HDMI. Let me know.

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

I have tried it on all inputs so far and it's doing the same including the HDMI'S as well! I have noticed when it restarts it doesn't always properly start (flashes the screen briefly) and may reboot a couple of times before displaying.
As I recall I have entered the service menu and haven't found any errors this was a little while back so I will enter it again to see.
I checked the pin on the psu for Power on/off and shortly after being turned off it goes high again which is coming from the main board to the psu to turn it on!
Also noticed on the remote control the brightness cannot be adjusted from the remote control from the dedicated buttons. I will have to look to see if it's the original remote for the TV. Buttons send out the infrared pulses on the remote without any issues.

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

The remote control isn't the original one for the TV so that's a red herring! I try not discount anything with trying to find where the issue lies,

[ReeceyBurger123]

Re: LG 42LG3000 Strange fault will not go into standby!

Did you disconnect the button board ?

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

Yes removed the side control buttons from the equation it didn't make any difference
I will have a look at the resistances in case the infra-red sensor which contains the power switch is shorted out, this isn't on the side controls of the TV.
I suppose it could be partially shorted which could trigger it.
I will have a look later on at it and let you know the results.

[ReeceyBurger123]

Re: LG 42LG3000 Strange fault will not go into standby!

All voltages bang on ? I had a Samsung plasma that wouldn’t shut down the panel, 5v was at 6 or 7v or so was due to an adjustment pot. You need to see what the pson and blon on signals do when you turn it off.

[ReeceyBurger123]

Re: LG 42LG3000 Strange fault will not go into standby!

I’m going to say a resistor somewhere might have failed, I did have this on a proview set also which a resistor for the blon circuit had failed Oc and the circuit stayed high and never shut down because the 5v rail was always up too, your looking at the mainboard being at fault I’d say.

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

The psu voltages are all good with respect to being within acceptable margins.
I then measured the voltages on the inverter (master) when the tv was on
BRI =3.2v
INV ON/OFF=5v
PWM-DIM= 3.3V
ERROR=0V
When TV in standby the voltages above were all 0V.

I then isolated each of the above pins from the inverter individually to see if it made any difference which it didn't.
I did notice that the ERROR pin was 3.2V on the master inverter when on and when isolated from the main board. I will have to look at that schematic to see if it is anything to worry about.
The pins were removed at the motherboard power connector.
Just checked the tactile push power switch on the TV set which wasn't partially shorted.

My immediate conclusion was the main board which was replaced without any differences to the fault! It's possible the main board supplied was faulty with the same fault, but I would have expected the issue would have been reported before if it was a common occurrence.
I am going to have a look at the ERROR circuit on the main board to see how it operates. I think I already discounted this however best to recheck.

[ReeceyBurger123]

Re: LG 42LG3000 Strange fault will not go into standby!

Yeah that’s bang on, why is the error circuit keeping the backlight up I do wonder ? I have had to replace countless controller Ics on them inverters and the on board capacitors fail too (high ESR not physically so check them) and occasionally the mosfets for them short out. Think Ive a video on my channel about the 42LG3000 inverters.

Edit: Check F9 at the main connector also.

[TRANSLTR]

Re: LG 42LG3000 Strange fault will not go into standby!

Hey,
maybe it would be helpful to take a look at the Power Off History in the servcie menu.

If you encounter something like POWER_OFF_BY_ACDET, this post may be helpful:
https://www.badcaps.net/forum/showpo...5&postcount=58

They had problems with switching from stdby/on in various combinations. The analysis and solution from densmith seemed to be helpful for their case and devices.

Do you have the name/number of the Mainboard? Maybe schematics?

[cheeky2]

Re: LG 42LG3000 Strange fault will not go into standby!

Hey,
maybe it would be helpful to take a look at the Power Off History in the servcie menu.

If you encounter something like POWER_OFF_BY_ACDET, this post may be helpful:
https://www.badcaps.net/forum/showpo...5&postcount=58

They had problems with switching from stdby/on in various combinations. The analysis and solution from densmith seemed to be helpful for their case and devices.

Do you have the name/number of the Mainboard? Maybe schematics?

Thanks for that I will look further into it.
I have finally managed to resolve the issue down to the power supply!
I changed the inverters no change.
Finally decided to change the psu which resolved it even though I was convinced it wasn't the problem and the issue lied with the main board.
So now that I have the TV working I will establish where the issue lies on the power board and I will update this thread when I have a solution to the issue.