New LG OLED no display

[Davi.p]

Re: New LG OLED no display

I'm not good in reading circuits but... the signal starts at the central pins of the 2 diode bridges, a diode takes out from the line a positive voltage that passes in a group of smd resistors, then arrive to maybe the base of a pnp transis., the collector is on a + supply tension (it feeds also the relais on top of the two PFC coils), there is also the cathode of a zener, it's anode makes a long tour and goes to the negative, the emitter of the pnp travels until enters to an ic, probably the REF pin of a 431, the upper pin of it is clearly at negative, the cathode is connected to the cathode of opto's led (its anode by a resistor travels long to an output of a probable TO220 5v Regulator). So when AC is present the pnp is off, the REF of the 431 is pulled low by the smd resis. (9103+0 values), the current doesn't flow to anode and opto led did not glow, so the output transistor is open and ACD is near 0v.

[tom66]

Re: New LG OLED no display

Interesting
Of course one way to see if this is correct is to use say a multimeter and see what it does on power up or power down.
If it goes high initially then goes low, or low then high, that would validate your idea.
Some digital multimeters are too slow for this, one area an analogue multimeter has benefits, or an oscilloscope of course.

[budm]

Re: New LG OLED no display

I am curious: Can you please provide the DCV of
1) 12VN (Always on 12V power supply provdided by transformer T101 and rectifier D201). BTW, I cannot read the label clearly, it looks looks like 12vN.
2) 12VT (switched 12V provided by switched MOSFET Q202 (P-CH), the feeding Voltage to Q202 Source pin is the 12VN),
3) 20VS is switched 20V provided by T101, rectifier D204, and switched MOSFET Q203 (PCH), the Voltage is fed to Source pin.
4) ACD is provided by OPTO IC105, the output is Emitter follower, the Collector is fed by R240, the other end of R240 is connected to 12VN, the output level looks to be clamped by IC202. So if you read the Vf on the LED pins on the HOT side, if it shows around 2VDC or do then the ACD Voltage should be present.

[Davi.p]

Re: New LG OLED no display

mmmmh, yes, i think AC det is normally low, if it was high the mainboard would be switched off and so the 12VTcon... then gets more body the thought of bad panel or bad tcon.

12VN is 12VM (mainboard), 20VS is VSound..

[budm]

Re: New LG OLED no display

According to OP, the 12VT_ON is present (post #8: 12VT_on has 3.6V) so the 12VT should then be present.
MOSFET Q202 for 12VT is not locked out by ACD signal, it is independent otherwise OP will not have 12vt_on at this point.

[Davi.p]

Re: New LG OLED no display

My message is another, the signal is not direct, ACD tells the mainboard that input line is going low, when it happens Mainboard cpu stop eeprom writing and shut itself off, as consequence Tcon have to go off therefore 12VT cannot be on, if i remember you teached me the ACDet function... :-)

[budm]

Re: New LG OLED no display

But at this point the 12VT_ON signal is present and ACD signal is low, the 12V and the 20V are generated by the same transformer that generates 12V STBY.
The main key at this point is that the 12VT_ON ins present and 12V is also being fed to the switched MOSFET that provides the 12VT.
The ACD is used to stop the main power supply from coming on if the incoming AC Voltage is too low, in this case the 24V power supply (Transformer T102) in this case, when AC is too low the TV will try to draw more current to maintain the regulated output Voltages.
At this point we know that we have 12VT_ON signal the OP will just have to check the Voltage on the GATE, SOURCE, and DRAIN pins of Q202, the GATE pin Voltage has to be 3 ~ 4VDC lower than the Source pin for Q202 to be on.
If OP does not have 12VT, then the main board cab also be locked out from sending the PS-ON and DRV_ON. There are more than one lockout signals beside ACD.

[Davi.p]

Re: New LG OLED no display

Sorry i'm on a stupid tablet now, i can't check pictures, i dont follow you perfectly, i go to bed, see you tomorrow or who knows, bye...

[Davi.p]

Re: New LG OLED no display

The ACD is used to stop the main power supply from coming on if the incoming AC Voltage is too low, in this case the 24V power supply (Transformer T102) in this case, when AC is too low the TV will try to draw more current to maintain the regulated output Voltages.

I don't understand this, i remebered that the mainboard shuts the tv off when line drop occurs, is it correct or not?

Sorry Budm, sometimes i go by memory, but this time i was wrong, i remembered Keshena said that he had 12VT, but he never said it. So let we wait Keshena news..

[Davi.p]

Re: New LG OLED no display

The OP is fallen into the tunnel of the posts??

[tom66]

Re: New LG OLED no display

I don't understand this, i remebered that the mainboard shuts the tv off when line drop occurs, is it correct or not?

Sorry Budm, sometimes i go by memory, but this time i was wrong, i remembered Keshena said that he had 12VT, but he never said it. So let we wait Keshena news..

Usually AC detect is used to mute audio and try to gracefully shut down if AC line is lost.
OLED panels might require some kind of synchronisation of the panel voltages, e.g. 24V needs to go off before 12V.
It also gives any smart TV software time to flush the caches to disk so that the filesystem remains intact.

[Keshenatech1]

Re: New LG OLED no display

Ok I was right the first time. The AC_DET was high, around 3.8V. The only missing signal was the DRV_On. I monitored the 24V and that Drv_on signal on power-up, and not even a flicker or surge. I also had a chance to talk with the person who picked it up at the customer's house and he confirmed that both the sound and picture failed. So I figured it's most likely a bad main board. So I ordered one on Ebay. I believe I diagnosed it correctly because with the new main board, I get the 24V and a display. However, the display is stuck in the WebOs message. It goes on and off every few seconds. There is no response to the menu button on the tv or remote. All I can do is turn it on and off. I let it run 20 minutes and it just won't come up. Did I get a bad board or is there something I can do to break out of this mode and get it to function?
https://www.badcaps.net/forum/pictur...&pictureid=811

[budm]

Re: New LG OLED no display

So ACD (AC Detect) = high = normal, same as Sharp TV.
It does sound like the main board has problem.

[Davi.p]

Re: New LG OLED no display

Yes, new mainboard seems to have a bad firmware or flash memory. Maybe is best to troubleshoot the original one, i suggest to find a spi flash on that board and if found remount it and try to switch it on when you freeze the spi. Also read spi content and check it with hex editor.

[Keshenatech1]

Re: New LG OLED no display

Sorry Davi, this is way over my head. Is the SPI flash similar to the 8 pin eprom we used to replace on the older TV main boards like the RCA's? I currently don't have the equipment to read or program one of those IC's. What would I need to get to read the chip? I'm pretty good with computer programming and I'm sure I could figure it out. It's just something I've never attempted before.
Also, if I got a bad board from Ebay, I really don't want to do any soldering or tampering with it and void any chance to get my $100 back. I emailed the seller and he wrote back to tell me he is out of town until Tuesday and he'll get back to me then with a solution. I'm guessing he may send me another board to try because he does have 5 of them for sale.
I also don't have equipment to replace BGA chips on main boards just because I do this part time and don't do a high enough volume to justify the $10,000 cost of a good BGA rework station. It would be nice to have one and I do enjoy soldering and fixing things myself but I only replace less than 1/2 dozen main boards a year and I can usually find them cheap on Ebay. This is the first one I've ever had not work. And this seller has 100% positive feedback.

One thing I did think of is that LG offers a firmware update for this TV on their website, one that gets put on a USB flash drive. Do you think it would be worth while to try it and see if the TV recognizes the drive and tries to update? Maybe updating the firmware would get it "unstuck"?

Do you believe the problem in my original board could be something simple other than the BGA processor, and repairable with a hot air pencil and basic soldering equipment? I won't mind messing around the the original board because it would probably just get recycled anyway. For what it's worth, I'm including the links to pictures of the board. If you have any suggestions on what the problem could be on my original board or where to start, please let me know. Once again, the symptom is no DRV_ON signal to turn on the 24V to the display, and also no sound. I'm thinking main CPU processor but that's only a guess. Thanks again for all your assistance, it's greatly appreciated!
http://assets.shopjimmy.com/media/ca...053201-top.jpg
http://assets.shopjimmy.com/media/ca...201-bottom.jpg

[Davi.p]

Re: New LG OLED no display

Yes the SPI is a sop8 chip that usually have a marking like 25Qxxx instead of 24cxxx of the eeproms, if you want to continue this job i suggest a more powerful programmer like RT809H or RT809F, but for a simple start you can buy for few dollars a CH341A with sop8 clip, with this you can read-write a chip in few seconds without desolder the chip if it is good. I suspect LG mainboards from LED tvs to ahead suffers from bad spiflash chips. I was just telling to repair original board. I dont know if putting an usb key can succesfully rewrite a firmware, but this can happen only on the replacement board that at least shows logo on screen.

[ThomasX]

Re: New LG OLED no display

Hello!

I do recognize this is an old thread, but since there's some really good info here and it very closely relates to an issue I am having with my LG OLED65C7, I thought I'd ask here.

I have the issue with the red LED blinking 3 times when powered on, then staying off for maybe 5-10 seconds and then the TV turns off and the red led goes on again.

I have measured the following while the TV is on

24VD = 24 volts
12VT = 12 volts
20VS = 20 volts
12VM = 12 volts (7.4-7.8 volts when TV is off!)
PWR_ON = 3.3 volts
DPC = 0 volts
ACD = 3.6 volts
12VT_ON = 3.5 volts
DRV_ON = 1.6 volts

I guess the odd ball here, that indicates where the issue might be, is DRV_ON that shows 1.6 volts, when it should be, I assume, 3.3 - 3.6 volts.

Any suggestions where to go from here?

Do I dare to disconnect the wire and inject 3.3 volts, or to just hook it up with one of the other control signals that gives the correct voltage?

Thanks!

[ThomasX]

Re: New LG OLED no display

Well, I used my brain and realized first thing to try is to disconnect the DRV_ON and check the voltage level. So, with the DRV_ON disconnected, it still shows 1.6 volts. So that means it is the mother board that is driving 1.6 volts.

Is that maybe then the correct voltage for this signal, or is it the motherboard that is broken? I'm guessing the latter.

[ThomasX]

Re: New LG OLED no display

And now I noticed that with the DRV_ON signal disconnected, there's no 24VD, which leads me to think that DRV_ON = 1.6 volts is correct.

The behaviour of the TV is the same with the DRV_ON signal disconnected.

[ThomasX]

Re: New LG OLED no display

So now I wonder what is the DPC signal?