LG 42LD650 please help confirm diagnosis


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LG 42LD650 please help confirm diagnosis

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elbow
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Mar 22, 2016, 9:03 PM

Post #1 of 9 (4639 views)
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LG 42LD650 please help confirm diagnosis	Can't Post

Hi,

Hoping to just have someone review my debugging of my broken set:

I have a 2010 LG 42LD650 set. Taking it out of standby with the power button results in a "pulsing" red power light and nothing else.

I have checked and I have 3.5V present on the power board and get 12V and 20V lines too when I take the set out of standby. So that's as it should be.

I have +3.5V on the ERROR line coming back from the logic board. That doesn't change with set in or out of standby.

I have schematics from a service manual and the ERROR line seems to be essentially the PGOOD line from the MAX17113 power supply chip on the logic board. From the data sheet on that chip that says that the chip output voltages aren't good.

Backlights do not come on when I bring the set out of standby. The Invertor-on pin is 0v.

But if I pull the inverter-on pin up to 3.5V then they come on as long as I hold it up.

So - in respect of the power board: I have all the power supply lines present from the power board, and the backlights work if I tell the power board to turn them on.

There's also no physical signs of trouble on the power supply board like blown caps or scorch marks.

So my conclusion is that the power supply board is good and my fault is (unfortunately) with my logic board.

Is my reasoning sound?

Thanks,
Elbow

lgpies
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May 28, 2016, 4:34 PM

Post #2 of 9 (4505 views)
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Re: [elbow] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

Elbow, Whilst I am not able to help you with your problem, perhaps you can help me with mine. You state you have the service manual, I have a 32ld490 which I am presuming is same 'range' as your set, I need to get into the service menus to check debug mode etc. could you possibly help me with this and provide me the method for accessing these menus. Your help would be greatly appreciated <br>

(This post was edited by lgpies on May 28, 2016, 4:35 PM)

vlolham
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Jul 19, 2016, 5:29 AM

Post #3 of 9 (3961 views)
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Re: [elbow] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

Hi,
I have exactly the same problem.
I already replaced the power board. no difference.
I suspect problem with logic board.
I'll let you know if any new development.
VL

vlolham
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Jul 19, 2016, 7:25 AM

Post #4 of 9 (3958 views)
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Re: [vlolham] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

I examine the voltage output 12V, 20V both are okay.
But PWR-ON is zero and screen is dead. if you short pin1 and pin9 on the power board connector (24pin) then screen back-light will turn on, this means your power board is okay.
Now, by investigating further the voltage +16 is missing on the cap C9153, so any IC connected to this voltage will be down most noticeable ICs are IC9100 IC9102, IC9103.
So now the focus is on VDD_LCM=16v , if I find anything further, I will let you know, good luck.
VL.

(This post was edited by vlolham on Jul 23, 2016, 4:46 AM)

vlolham
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Jul 23, 2016, 4:34 AM

Post #5 of 9 (3930 views)
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Re: [vlolham] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

MAX17113 Datasheet (Multiple-Output
Power Supply for LCD TV) confirms that pin 35 is +16V 1.5A output.
I must assume pin4 is the source voltage input 25V but at the same time pin 24 is shown as voltage in! anyhow; at this stage I assume the IC MAX17113 is faulty.
One may try to inject a +16V from an external source to C9153 capacitor to see if the TV will work or not..... I will try it anyhow. standby!

VL.

Carpenter
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Dec 5, 2016, 11:09 PM

Post #6 of 9 (3651 views)
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Re: [vlolham] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

How did it end up?
I solve the same problem, +16V 1.5A output is down too , but I thing this output is down necouse EN2 is low

vlolham
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Dec 7, 2016, 2:33 AM

Post #7 of 9 (3624 views)
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Re: [Carpenter] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

My SMD chip removal device wasn't good enough for the job, I replaced the chip but on the other side of the board some SM resistors and caps moved or fell off Laugh

So, I give up on this one. Better luck with the next job.
Nevertheless I was on the right track.
cheers & good luck.

NoahCann
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Feb 8, 2017, 9:02 AM

Post #8 of 9 (3482 views)
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Re: [elbow] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

I think you can find a professional help here! <a href="http://skywritingservice.com/blog/need-remote-work-first-check-all-pros-and-cons">http://skywritingservice.com/blog/need-remote-work-first-check-all-pros-and-cons</a> will help you to decide do you really need a remote job or not!

(This post was edited by NoahCann on Feb 8, 2017, 9:02 AM)

ixxbigdxxi
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Feb 12, 2017, 4:35 PM

Post #9 of 9 (3448 views)
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Re: [elbow] LG 42LD650 please help confirm diagnosis [In reply to]	Can't Post

This models along with the 52ld550 and 42ld550 (plus many other models from this year) are notorious for having issues due to bad solder joints on the main board. That is more than likely your issue. Symptoms will include backlight flickering, scrambled picture, hdmi ports not working, the screen stuck at the LG logo, or just a red flashing light with no picture. I have 3 of these models and had issues with them all. I know it sounds odd but sticking the main board in the oven for about 10 mins at 375-385F did the trick on all 3. Don't believe me? Google those models and the word oven and you will see tons of results lol. Still using these tv's to this day. Good videos on YouTube also on baking lg boards. <br>

(This post was edited by ixxbigdxxi on Feb 12, 2017, 4:55 PM)

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