LGOLED55B7V Clicking and dead screen.

[Donny2derby]

Picked this up other week and when I originally looked at in the sellers house I got 3/4's of a working screen and some horizontal lines across the 1/4 of it which was dead/black.

Just tried powering it up at home and now all I'm getting is a clicking and some very faint lines on 1/4 of the screen whilst the entirety of it is dead.

When using the remote I get two red clicks on the standby. Not sure if this means anything or helps. The same when I use the manual power up.

Help appreciated. I'm an electrician, I've fixed a few in the past so not a total newbie. I have a digital meter with diode/capacitance/oscilloscope, a 30vDC power supply and a steady flow of Yorkshire tea with me to help fault find. I'm in for the long haul.

Thanks in advance.

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Ok I’ve found a cap (marked up C612) on the main power board which is showing open circuit. Tested in circuit but all the others I’m checking are showing what their capacitance is.

Is this too simple or could it be the culprit?

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Can anyone help me?

I've found these 2 cables running from the main power board. One to the Tcon and one to main board (I believe)

Any one able to tell me what the 24vd and 12vt are? I'm assuming 12vt is volt. And on P202 DRV.ON, DPC. And the other abbreviations are.

[lotas]

Re: LGOLED55B7V Clicking and dead screen.

Here's the service manual, take a look.

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Thanks for that lotas.

However the manual gives a guide of how to repair the no video/no audio fault as would be given to a service repair tech and simply states to check various voltages and then replace the main board. Not exactly what I was hoping for.

Now I know you know your shit so can you point me to where I should be checking for voltages and what I should be looking for?

I understand this is probably annoyingly repetitive for you and others on here but how am I supposed to learn if nobody tells me where to start looking?

Thanks.

[EazyBone]

Re: LGOLED55B7V Clicking and dead screen.

The 24 and 12 are volts yes. Disconnect the main and tcon and test for them. At least that's how it was on mine. There was also a 3.3 or 5v can't remember standby I believe.

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

You’re a gent Mr Bone.

I’ll get on it again tomorrow and post the findings.

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Connector P202 is dead as a dodo.

P201 does have some voltages present but not in all the places expected.

Pin 4 right hand side as I look at it on the layout on the reverse of the silk screen marked 12VM has 7.9vDC

Pin 9 right hand side marked 12VM has the same 7.9vDC

The other 2 pins which have voltage are both left hand side. Pin 5 marked 12VM has 9.7vDC

Pin 9 also marked 12VM has the same 9.7vDC.

I’ve also located the VCC pin and noted there’s no voltage there either. I’m led to believe this is some sort of input voltage for some IC’s??

I should also add that the large caps are holding onto their voltage for what seems an unusually long length of time. I’ve had the power board disconnected for around 10 minutes now and they still have 270v in them!

Anyone able to offer any pointers? Thanks.

[EazyBone]

Re: LGOLED55B7V Clicking and dead screen.

I mean, I'm just learning here but. When main and tcon were disconnected on mine I was able to get the correct 12v readings/20v I believe. Are they disconnected and getting those readings?

When hitting the power button those 20v pins would try and go up to 20 to tcon and drop into nothing.

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Yep that’s with them disconnected mate.

There are numerous caps I’m not happy with so the plan is to replace those and see where I stand after that.

I’ve got a few at work but ordered the ones I need from aliexpress and will recap them all when they arrive off the slow boat from china.

I’m not even getting my red standby light on the telly so something clearly amiss on the power board.

[Davi.p]

Re: LGOLED55B7V Clicking and dead screen.

12VM=Volt Mainboard, 20VS=Volt Standby, 12VT=volt tcon, 24VD=volt display..
how much 20vs are? get a 3v battery and place it on 12vt-on, drv-on, pwr-on, so the tensions goes on and test all them..

OLED55B7V

[Diah]

Re: LGOLED55B7V Clicking and dead screen.

you have short cell on the Panel module .. SOS signal come to MB turn off the set if you disconnect only the black cable between the Power boards and the T-CON ... it will start and stay on ( sign are the Audio Optic port lit red ) none repairable ..

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Thank you both for your help.

I have found a high voltage diode on what I believe to be the chopper circuit which is passing both ways.

I will replace that just in case that is causing another issue and then do what you suggest Diah.

[Davi.p]

Re: LGOLED55B7V Clicking and dead screen.

diode where? measuring how much? with a desoldered leg?

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Diode is marked D601 Davi and I believe it’s on the PFC part of the circuit.

At the minute I don’t have it de-soldered. But there are 2 sets of 2 diodes in parallel in the vicinity and only that one passes both ways.

I’m back at work Saturday night which is where my de-soldering equipment is. Once I’ve taken it out and tested it out of circuit I’ll let you know the results.

But this could be causing the issue with no power onto the primary side of the transformer yes??

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Ok then. Q601 & Q602 are both N channel mosfets. They each have a diode on their respective heatsinks with them and a pair of inductors. (Lb603/04) and Lb601/02 they both seem to feed or be fed from inductors L601 and L602.

I also have a couple of IC’s (601 & 101) for which I can’t seem to find a schematic that matches its physical appearance. I.e the Pinout schematics I can find on the internet have 7 or 8 pin layouts and they appear on the PCB to have 14 pins.

Am I making sense or does the above read like gibberish and I’m best off throwing in the towel on this one?

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Further info.

The outgoing side of the bridge feeds D604 via an inductor. And the positive side of both the main 450v caps goes to the cathode of D503.

Both those diodes test fine when removed from the circuit so I'm happy with things up to that point. Capacitor C624 sits in between those 2 diodes.

Where does or should my voltage be going after those diodes?

I have other small possible mosfets marked up Q603 & Q606 in the same part of the PCB that are both in series with a number of resistors.

This tv cost me £100 so I hope this helps explain my desperation to exhaust every possible issue it may have in my quest to resolve the problem. If I go out on my shield then fair enough but I'm not done yet haha.

[Davi.p]

Re: LGOLED55B7V Clicking and dead screen.

first test every component on heatsink and tell me which one is measuring bad pointing at your previous photo, it's useless that you tell me only D601, Q602 bla bla, when i don't know where them are and which type are...

[Donny2derby]

Re: LGOLED55B7V Clicking and dead screen.

Out of circuit both the mosfets and diodes on each heat sink test fine Davi. The two diodes are D603 & D604. The two inductors which supply them are L601 & L602.

I have voltage from my bridge rectifier onto the inductor but apparently nothing coming off it! Could be getting somewhere!

350v coming off the bridge but dead across legs EL45 & 46!

0 resistance across the inductor as well.

[Davi.p]

Re: LGOLED55B7V Clicking and dead screen.

Ok Donny sorry for my previous mistakes, now i'm back at home from my vacations with a big handy tablet not the small cellular..
1) 20VS=20V Sound , not standby
2) 12VM= 12V main, that is the main supply that feeds main board also in standby state, but in standby it is normally less as you measured, it's a normal behaviour of recent tv..
told this i guess you have a good power bd but a problem in the screen or tcon bd, so i think you can skip the boring pass of testing alone the power bd, but if u want to proceed cautionally in the post 11 i've already told you how to do that but you haven't done it.. then you can try and purchase a good tcon possibly took from a smashed screen, or you can do some measurements before..