New LG OLED no display

[Keshenatech1]

I was asked to look at an almost brand new LG OLED55B7A-U, manufactured in January of this year, just bought by a customer in July, and it died already. This is my 1st OLED so I'm hoping someone with experience in these might be able to give me some direction. Standby light is on, and TV does turn off and on with remote. Standby light blinks 3 times then stays off until it's powered down. I was unable to tell if there is sound because with no display I can't tell what input signal it's set on.
I did a check for voltages on the power board and everything is there except one voltage. On P202, the connector that goes to a board in the center of the panel, the 24VD only has .565 Volts on it. On P201, the connector going to the main board, the P_ON signal has 3.6 Volts, and the pin across from it labeled ACD has just over 3.8 Volts. Is that ACD signal what turns on the panel voltage? The 12V on that connector is there, so is the 20V and 12V on P201. So before I order a new power board, I just want to make sure that I'm not missing a signal that's supposed to turn on that 24V. I did try it with P202 unplugged in case that panel board was loading down the 24V, but it won't even attempt to turn on with that connector unplugged. I did give the board a once-over in that 24V area and didn't find any obvious open or shorted components or anything else suspicious. The power board is a P/N EAY64510701. Does anyone have a schematic of this board or know what turn-on signal it requires to get this 24V? Is replacing it recommended, or could the problem likely be caused elsewhere in the set, such as the panel? Sorry for so many questions, this is a new technology to me so I'm hoping to learn more about how they work. BTW be careful when working on this board. Caps hold a 300V+ charge for several minutes after unplugging it so it's highly recommended to discharge them, as on most power boards.

Thanks.

https://www.badcaps.net/forum/pictur...&pictureid=808
https://www.badcaps.net/forum/pictur...&pictureid=810
https://www.badcaps.net/forum/pictur...&pictureid=809

[Davi.p]

Re: New LG OLED no display

I suspect that in all newer TV tecnologies (LED,OLED) the most probably part that can fail so soon is the panel, it is the most difficult to manufacture... i would not spend money in a new board, you can study a bit of them before eventually raise the white flag.. If 24V (VoltDisplay) did not come then maybe mainboard dectects a fault in the panel and/or the ""TCON"", so why don't supply this 24v to it and search for voltages on it? If you don't want study all tcon that tooks some hours (?) at least test all bigger capacitors, if no voltage on it it's maybe a problem on it...
At last post a big picture of the P.supply front and back, no shadows please.

[Keshenatech1]

Re: New LG OLED no display

I agree, that's why I was trying to figure out if I had the correct turn on signals before ordering the board. That's why I'm asking if anyone knows the correct state of the signals so I can compare my readings before calling the board bad. Also if I knew the correct signal voltage, I could power the board up on the bench and see if I can manually turn on the 24V to test it that way.
There seem to be 3 control lines, Pwr_On which obviously turns on the main voltages. Then there are 2 more, ACD straight across from the Pwr_On, and also DPC in the upper left top pin. DPC measured around 3.8V but unfortunately I did not get a reading on DPC because I didn't notice it until just now. I have the power board in front of me but the rest of the TV is across town. Thanks much for the reply, and any suggestions are greatly appreciated.

I hope you don't mind me using Shop Jimmy's pictures of the board. My phone camera isn't that good and they have a much more clear image than I can get.
http://assets.shopjimmy.com/media/ca...510701-top.jpg
http://assets.shopjimmy.com/media/ca...701-bottom.jpg

[Keshenatech1]

Re: New LG OLED no display

One other question. I actually found the service manual for this TV online. I'm going through a troubleshooting flowchart for sound, no video. It says to check the Vx1 Lock Voltage before replacing the power board. Do you have any idea of what the Vx1 Lock Voltge is, and where to measure it? Thanks again

[Davi.p]

Re: New LG OLED no display

SJ photos are the best...
For the SM i don't mind now, i'm watching the PSU.
First i would check the 2 power mosfets Q253-Q254 on heatsink and 2 pwr mos. SMD Q123-Q124 near the top 24v transfo, then check the marking of the IC215 in smd near the output mosfets and its datasheet, it controls the switching of the 2 rectifier mosfets. For the ACD, it means probably the common AC-detect signal but i think it's ok since usually an high state means it's ok. Check the 3 glass fuses especially F102. I have not found the 24vd switch for now.. but i think is DRV_ON that goes to some components (check the marking of Q252 in sot23, it's maybe a 431) and then to the opto IC107(diode side).

[tom66]

Re: New LG OLED no display

You need to establish if it is the power board or not before going head first into testing parts on it.

What do DRV_ON and PWR_ON and 12VT_ON do when you press the standby button or turn the TV on. I expect they toggle from say 0V to 3.3V. If they do not it is not the power board at fault -- the main board is not telling the board to turn on.

Also a mark of appreciation, LG's 55" OLED pulls 10.6A at 24V? Bloody hell, that's gonna be bright. I wonder when it power limits...

[Davi.p]

Re: New LG OLED no display

Yeah, right, it is possible the power sequence is: mainboard>Tcon>panel. Maybe the tcon detects a fault on itself and tells the mainb. not to switch on the 24v-panel, or there is an initial glow of the 24vd, tcon detects overload on panel and switch it off...
anyway if one suspect panel problem (no one can repair it i guess) before or after one have to test at least the PSU to be able to sell it. Do you have in USA tv with video out like SCART in Europe? (to test mainboard).

[Keshenatech1]

Re: New LG OLED no display

I stopped back there today on my way back from doing laundry. I found that DRV_on pin also after I had posted so I was curious to test it. It only had .7 volts on it. Pwr_on has 3.3V 12VT_on has 3.6V, ACD had close to zero volts. So yeah if that DRV_ON signal has to be high for the 24V to turn on, then for sure the problem is elsewhere besides the power board. Could be a bad main board, bad T-Con, or the panel itself could be bad. But is there any way to narrow it down before ordering parts? I wish we had another one of those in stock to compare readings and swap boards, but no luck. And the new ones we have coming are a 65" upgraded version.

[Davi.p]

Re: New LG OLED no display

Wait... in the first post ACD was 3,8v. Now is 0v? This sound not good, i guess ACD is ok at 3,xx v. Check newly, if i'm right It detects a wrong supply tension from AC outlet.

[Keshenatech1]

Re: New LG OLED no display

I think I made a mistake in my 1st post going from memory not having it in front of me. When I went back today, The PWR_ON was 3.3V, the 12VT_On was around 3.6, ACD and DRV_ON are close to zero. I may have to check it again but the shop is closed until Tuesday now. I'm taking tomorrow off for the holiday. I work 40 hours during the week at my regular job and spend most of my nights and weekends on TV repairs at the other place. Definitely time for a day off, I'm not remembering voltages clearly. But I think the important signal here is the DRV_ON. I believe that is what is supposed to turn on my panel voltage so I'm trying to figure out if the problem is the main board, panel driver board, or panel itself. Is there any way to narrow it down short of starting to order and swap parts?

[Davi.p]

Re: New LG OLED no display

I have already suggested to inspect for supposed AC-DET signal, it is connected to the optocoupler IC105, and other components, one can follow the signal path from the AC pins of the 2 diode bridges and check if i'm correct that it must be high signal to be OK. If you want i can list the components to check, but i wanna leave to you the game...
To make it short, check first on the opto, primary side (diode) if it has something like a 5v A-K (the supply line comes from a supposed linear reg. on bottom, Q105), if it has not, jump the cathode to primary gnd, if it has, check on the phototrans. that there is many volts at the collector.

[Keshenatech1]

Re: New LG OLED no display

Just to clarify, is that an input signal into the power board, or an output signal from it? BTW I left the power board in the TV at the shop so I won't be able to do anything further until Tues night, I'm done for the weekend. I'll double check it when I get back there and let you know for sure what state it's in. Thanks much for your help.

[Davi.p]

Re: New LG OLED no display

ACD or AC-DET is the PSU that tells the mainboard that the input line is ok, so is a psu output.

[tom66]

Re: New LG OLED no display

Yeah, right, it is possible the power sequence is: mainboard>Tcon>panel. Maybe the tcon detects a fault on itself and tells the mainb. not to switch on the 24v-panel, or there is an initial glow of the 24vd, tcon detects overload on panel and switch it off...

if there is no connection between the power board and T-con other than to carry the power for the OLED panel how would you propose this function?

Do you have in USA tv with video out like SCART in Europe? (to test mainboard).

Not in USA, but this trick has not worked for almost 10 years in Europe now... I cannot think of a single non-CRT TV I have had that would let you output analogue video over the SCART port.

[Davi.p]

Re: New LG OLED no display

if there is no connection between the power board and T-con other than to carry the power for the OLED panel how would you propose this function?

I mean, first PSU power on the mainboard, it tells to PSU to switch on tcon (12VT), then to switch on Panel supply (24VD), if tcon detects panel problem tells the mainboard thru serial comm to tell the PSU to switch off 24VD.

[tom66]

Re: New LG OLED no display

I mean, first PSU power on the mainboard, it tells to PSU to switch on tcon (12VT), then to switch on Panel supply (24VD), if tcon detects panel problem tells the mainboard thru serial comm to tell the PSU to switch off 24VD.

yes...exactly...
but you must test DRV-ON etc first before you go and say if the power board is bad and start checking fuses and transistors for shorts.

[Davi.p]

Re: New LG OLED no display

But at least the AC-DET must be high i think..

[tom66]

Re: New LG OLED no display

But at least the AC-DET must be high i think..

It depends if it's active high or active low type.

[Davi.p]

Re: New LG OLED no display

mmmh... watching the circuit it seems active low.. low=ac present... it's a sin..

[tom66]

Re: New LG OLED no display

mmmh... watching the circuit it seems active low.. low=ac present... it's a sin..

How'd you determine this, out of interest?