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Old 04-10-2020, 10:13 PM   #1
ngth82
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Default LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

TV: LG 47LE5400-UC.AUSWLJR

Symptoms: When i press the power button, i hear the relay click. The front panel touch buttons illuminate and they make a sound when i press on them.

No backlights (even for a brief moment), and the optical audio light is not on. Power supply appears to be fine though (measurements are at the bottom).

The mainboard sends the "power on" signal correct as well as PWM DIM, but DRV_ON is not sent.

I disconnected the cable between the SMPS and main board. I jumped 3.3STBY to POWER_ON as well as 3.3STBY to DRV_ON with two 10K resistors. The backlights came on just fine (yay!). The string tested good as well with the LED tester with the unit off.

I'm suspecting that the main board has an issue. Likely a problem with the main processor BGA.

On a side note, I obtained a 55" version of this TV (LG 55LV5500-UA.AUSYLJR) in 2016 and it failed in the same manner. I ended up replacing the main board for that one.

Anyway, I measured the voltages with the TV in STBY and when it's ON. Looks like i'm missing DRV_ON. What's the chances it's the micom firmware? (i'm assuming remote).

Any thoughts on this would be greatly appreciated. If there are no other suggestions, this thing will get a quick "heatgun treatment" to the BGA under the main heatsink to see if that temporarily fixes it.

Code:
P201, odd pins are the top row, even pins bottom row.			
			
Pin	SIG	V_OFF	V_ON
1	PWR_ON	0	3.329
3	20V	0	21.26
5	GND	0	0
7	GND	0	0
9	3.5V	3.49	3.438
11	3.5V	3.49	3.438
13	GND	0	0
15	GND	0	0
17	12V	0	12.46
19	12V	0	12.46
21	12V	0	12.46
23	SIN	0	0
2	20V	0	21.26
4	20V	0	21.26
6	GND	0	0
8	GND	0	0
10	3.5V	3.49	3.441
12	3.5V	3.49	3.441
14	GND	0	0
16	V-sync	0	0.252
18	DRV ON	0	0.043
20	SCLK	0	0.21
22	PWM DIM	0	2.917
24	ErrOut	0	0
Attached Images
File Type: jpg Photo Apr 10, 7 54 55 PM.jpg (564.0 KB, 17 views)
File Type: jpg Photo Apr 10, 7 55 05 PM.jpg (723.1 KB, 19 views)
File Type: jpg Photo Apr 10, 7 55 22 PM.jpg (578.5 KB, 14 views)
File Type: jpg Photo Apr 10, 7 55 27 PM.jpg (580.6 KB, 14 views)
File Type: jpg Photo Apr 10, 7 55 35 PM.jpg (783.0 KB, 10 views)
File Type: jpg Photo Apr 10, 8 07 18 PM.jpg (504.2 KB, 11 views)
File Type: jpg Photo Apr 10, 7 55 40 PM.jpg (740.2 KB, 12 views)
__________________
-Thomas
I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.
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Old 04-10-2020, 10:52 PM   #2
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

No DRV_ON is probably BGA failure (common in LG LE, LV and LS? series). Repair services for the main board on ebay. I would try a hair dryer on the processor first to confirm.
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Old 04-10-2020, 11:00 PM   #3
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Thanks for the quick confirmation. I'll give this a go tomorrow.

-Thomas
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Old 04-11-2020, 01:14 PM   #4
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

I heated up the main processor and surrounding board area with a heat gun. Works for now. I'll let this TV run for a few hours today and see how it goes. My other option is to stick it in the dedicated toaster oven for electronics if it fails again.

Thanks! Onwards to the next item.
Attached Images
File Type: jpg Photo Apr 11, 12 47 01 PM.jpg (459.3 KB, 12 views)
File Type: jpg Photo Apr 11, 12 47 14 PM.jpg (515.0 KB, 13 views)

Last edited by ngth82; 04-11-2020 at 02:01 PM.. Reason: Add pictures.
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Old 04-11-2020, 02:01 PM   #5
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

The hair dryer trick is same as wrapping a ps3 or laptop in a blanket to get them to start. The cracked solder joints will expand enough to make contact. I have tried to bake boards before but the problem came back in a few months (tried on ps3 and laptop). Proper repair is to reball.

Last edited by neilc6; 04-11-2020 at 02:02 PM..
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Old 04-11-2020, 02:04 PM   #6
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Agreed. I just updated post #4 with pics. I agree a proper fix is a reball, LG and authorized repair shops want an arm and a leg for a new main board. eBay "repair services" want ~$50 just not worth it.

I got this TV for free, it can just be given away for free to a family in need (or hang yet another TV in the garage... already have two. A third is excessive lol)

I was combing FB market place and saw a dead TV local to me, just couldn't pass up the opportunity to have a crack at it.

At the very least, this thread may help someone else in the future.

Thanks!
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Old 04-11-2020, 02:12 PM   #7
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Some will run a long time if a fan solution is implemented to stop the overheating.
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Old 04-11-2020, 02:15 PM   #8
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

good call... i have a thin fan that may fit inside the chassis. I'll double check the clearance to the back cover though. If a fan were to be added, i'd like this to all be internal.
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Old 04-11-2020, 02:19 PM   #9
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

I avoid any LG LV, LE, LS series because of the BGA issues. Proper reballing is $100 and these models typically aren't worth that much (old and not smart).

Last edited by neilc6; 04-11-2020 at 02:20 PM..
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Old 04-11-2020, 09:32 PM   #10
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

I agree -- this series of TVs are notorious for failures.

It still works after 7 hours of running. No guarantees for longevity, but it'll be donated.
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Old 04-11-2020, 10:46 PM   #11
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

You will need to let it cool down and see if it powers back on. The processor running hot is actually good for the BGA connections once they are intermittent.
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Old 04-11-2020, 10:47 PM   #12
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Agreed. It'll be powered up again in the morning. The unit is in the garage. The low is supposed to be around 39 degrees tonight. There's plenty of opportunity to let nature do the thermal differentials.
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Old 04-12-2020, 04:00 AM   #13
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Well sounds like a dif statement, here's a WELL KNOWN DOCUMENTED FACT about why you don't want your bga overheating OR running hot, it's in the first sentence ffs. If anyone doesn't believe this one article there are THOUSANDS more, it's simple and easy to understand: https://www.singularityeng.com/singu...g-hot-in-there

Last edited by nomoresonys; 04-12-2020 at 04:31 AM..
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Old 04-12-2020, 10:33 AM   #14
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Quote:
Originally Posted by nomoresonys View Post
Well sounds like a dif statement, here's a WELL KNOWN DOCUMENTED FACT about why you don't want your bga overheating OR running hot, it's in the first sentence ffs. If anyone doesn't believe this one article there are THOUSANDS more, it's simple and easy to understand: https://www.singularityeng.com/singu...g-hot-in-there

+1

At work, we take our products through temperature cycling and HALT (highly accelerated life testing) in a temperature chamber. The basic premise is exactly what is pointed out in the article and you stress the board at the max operating conditions, and min operating conditions and observe failures (device failure - permanent/temporary, and thermal failure conditions - e.g. Tcase temps exceed max derated values per the device datasheets.

The key here is for a vendor to take it through all "four corners" -- high temp (max operating temp), low temp, high voltage (all rails margined on the high side tolerances, low voltage (all rails margined on the low side of the rail tolerances).

neilc6 isn't wrong about devices working when it's warm vs cold though. Thermal expansion can cause failures to "go away" at least temporarily. Sure, it is NOT good for the system to run outside of the designed thermal boundaries though.
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Old 04-12-2020, 11:03 AM   #15
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

This is what I read " The processor running hot is actually good for the BGA connections"
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Old 04-12-2020, 11:46 AM   #16
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

BGA failures are caused by the leadfree solder balls cracking and losing connection between the processor and the circuit board. This problem is found in a few products including TV main boards (LG LE LV LS and Vizio M series), PS3s, Xboxes and laptops. With PS3s and laptops, one solution is to wrap it in a blanket powered up to get it warm before trying to turn it on. This would be equivalent to heating the processor with a hair dryer. This trick works because the heat expands the solder balls to make better contact and the contact will be maintained with the device hot. If you let the device cool down, the balls will contract and will loose contact again. I had a laptop where using the blanket trick, I could consistently get it to turn on and it would never turn on when cold. I eventually tried baking the board but it only lasted a few weeks before the problem came back. Running the tv for a long period isn't the only test. You need to let it cool down and see if it starts up again.

Last edited by neilc6; 04-12-2020 at 11:49 AM..
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Old 04-12-2020, 12:01 PM   #17
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Detailed article there, I think these tv makers are using components that will fail in a year or two, on purpose=planned obsolescence: https://www.google.com/search?client...d36c80f48f.pdf
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Old 04-12-2020, 12:04 PM   #18
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

What a fan solution does is keep the cycles from being too extreme as in the chip doesn't get as hot during operation, greatly improving life span.
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Old 04-12-2020, 12:15 PM   #19
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

Had a 40 inch samsung not long ago, had a blown transformer on the inverter board, I'm pretty sure the only reason was the back cover was all metal and rested just about right on top of the inverter and all the other boards, no space between no way to do anything but overheat daily til something blows. Then I guess they just assume you will buy another tv from them.
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Old 04-12-2020, 01:34 PM   #20
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Default Re: LG 47LE5400-UC.AUSWLJR - no backlight; no DRV_ON signal

I powered up the TV a little while ago - still works. I'm not under any impression the heatgun will be a permanent fix. Keeping the device cool has its merits.

In any case, the heatsink fins for the processor is very thin. The backcover is almost touching. The cover has perforated holes in this region. Maybe i can bolt on a 80 mm PC chassis fan on to the outside chassis using the existing holes. I can power it from the 24V line and use a variable switching supply board to regulate it down to 12V. Ideally any mods would be kept inside the chassis and hidden. Clearly not possible here.

Last edited by ngth82; 04-12-2020 at 01:40 PM..
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