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**newtothis** · 02-20-2015, 05:10 PM

Re: LG 42LE4500, Int No Backlights...

Yeah very common fault and a very expensive replace of a PSU. I tracked one back to the drivers IC controller before but parted the set out instead of repair

**Alastair E** · 02-20-2015, 06:35 PM

Re: LG 42LE4500, Int No Backlights...

Well--I plan on doing some more potching to this one....
--Got a bit distracted this evening--did summit daft and bought a 4K set cheap....

It looks as though the LED Driver feeds back to the LED main PSU on the PSU mother-board, and depending on that signal, adjusts the voltage supplied out to the LED driver board.

Maybe its possible to fool the thing into giving a more appropriate supply to run the LED's closer to the correct brightness,--and to hell with that complicated and daft unreliable LED Driver....
Early testing indicated that the LED strings have 100V across them--when the set was actually working as intended, although the notation on the board indicates only 89V at 900mA
--It all seems WAY overly complicated to effectively just light up a string of LED's--My Christmas-Tree lights ain't complicated--why should this heap of junk be!!

Unfortunately--As with all LG sets, the PSU schematics aint available, so its a case of fiddle and see, thankfully the LED PSU seems fairly simple, and is a sorta duplicate of the other multi-rail supply on the board, the chip looks the same so should be able to do summit....

**jakirsama** · 02-21-2015, 05:07 PM

Re: LG 42LE4500, Int No Backlights...

you need to need to change the psu here is one for £55
http://www.saelectronics.co.uk/lg-42...-yp42lpba.html

**tom66** · 02-21-2015, 05:35 PM

Re: LG 42LE4500, Int No Backlights...

The output voltage is probably boosted separately because other supplies (13V, 24V) run off that transformer. The LED strip is a large load, likely over 90% of the SMPS load, and so dictates the regulation of the transformer. If you set the output to 100V and bypass the converter you may find that the 13V rail (or whatever low voltage rails come off it) will beat with the PWM frequency... You will also probably find the 100V output will vary with the audio level or T-con processing etc which will cause backlight flicker.

This is a common set up in most LED TVs, generate an unregulated high voltage then boost/buck it to the exact required voltage. Means the power supply can focus on regulating the important 13V/24V/etc rails whilst letting the LED supply vary in operation.

You can wind the transformer to improve regulation but generally you can only regulate one rail at a time, so the other rails are "slave" to the regulated rail and must either be unregulated or draw little current.

**Alastair E** · 02-22-2015, 06:50 AM

Re: LG 42LE4500, Int No Backlights...

I hear ya Tom--But!

This set uses an entirely different stage/transformer for the 'small' supplies, and a separate regulator/switcher/double MOSFET and transformer from the 300V reservoir lytic...

Basically, There's two independent stages, one for everything else and one for the LED supply.
I think messing with only the LED one shouldnt affect (As its not in any way connected to as far as I can see) the other supplies....
--Still need to get back to it, maybe later today.....

Jakirsama--

The day I fork out £55 for a S/H PSU of dubious origin--be the day I hang up my multi-meter and give up TV repairs!!

I just NOT 'DO' changing expensive boards--Cheap yes, Expensive--I DONT do!!---Thanks for the info anyway, appreciated.

**tom66** · 02-22-2015, 11:10 AM

Re: LG 42LE4500, Int No Backlights...

Are you sure? The 5VSTB transformer looks too small to also provide 13V for audio and T-con power.

LG are unlikely to over-complicate the design without good cause. They will be very cost conscious.

**Alastair E** · 02-22-2015, 01:34 PM

Re: LG 42LE4500, Int No Backlights...

Absolutely Certain!

The 100V LED rail is generated by a tiny--sorta surface-mount type transformer, having Mylar print coils, that sits in a hole cut in the board and has a full wave bridge-rec on its output.--Gets damned hot too--even when the set is 'normal'
--The Other transformer--for what its actually doing (Supplying everything else)--is huge!

I tried in vain 'frigging' the feedback to the controller chip, no matter What I did around it and the two Opto's all I could ever get was 73V--or no function of that stage at all.

I changed tack and re-fitted the original LED Driver-board, but left the Output side thats connected to the LED strings disconnected and retained my additional wiring on the earthy ends of the strings attached to the neg of the 100V LED de-coupler caps/bridge-rec.

I also disconnected the 'Err' pin from that LED Controller board and the 'FB' pin that seems to go via some trannies etc to the opto's.

This left the set driving the LED's at 105V when first initialises then 73V after 5 seconds the 'FB' pin going to from 0 to 2.5V at the same time.

Through a 100 ohm, I attached the 'FB' print on the mother-board part of the PSU to deck.
--This gave 105V continuous to the LED strings which didn't drop.--105V is Too Much, so I used a 12K resistor from the 'FB' print to deck, which gave 85V dead on and a nice bright picture. PSU 'nominal' on this rail is 89V so I'm happy leaving at 85V

So--Conclusion--to Potch one of these terrible PSU's with this daft LED Controller, is reasonably easy-

Disconnect ALL the pins on the Output side.
Wire the LED strings in parallel, and connect direct to the LED Bridge-rec. (Neg leads to neg of Bridge)

Disconnect the pins (dry off the joints) on the 'ERR' pin and the 'FB' pin of that sub-board, --if you can --remove those pins from the LED Controller-board completely.

Put a 12K on print side of the PSU board, from the 'FB' print to convenient earth on board. This sets the drive voltage to the LED chains to 85V Using a 10K the voltage is 87V. I settled on 85V as this gave excellent brightness and less apparent temperature of the LED strings.

Set has now been working for an hour or two, no problems at all,--although obviously the Backlight in the set's settings is not adjustable.

**JeffJ** · 02-24-2015, 02:04 PM

Re: LG 42LE4500, Int No Backlights...

You wouldn't be willing to post a picture with what chip is suspect specifically? I am going to my Dads tonight to crack open his LG 47LN5750 tonight, it spontaneously is dim now. Its 2 seconds to black. its 13.5 months old :/

I know the power-supplies differ, but i suspect the same type of issue. Will be testing the Secondary to the LEDs.

**Alastair E** · 02-24-2015, 02:41 PM

Re: LG 42LE4500, Int No Backlights...

Sorry--I boxed the set up ready to go back.....

Cant miss the control-chip, Its on the sub-board, and connected to an array of 16 transistors that go to the LED plugs.

BUT IF your set hasn't the same PSU then its sure to be completely different!
Here's the board that I had--
http://www.ebay.co.uk/itm/TV-Part-EA...item58be37e46b

--There's two different versions of PSU for this set for instance--with different sub-boards!

**JeffJ** · 02-24-2015, 02:52 PM

Re: LG 42LE4500, Int No Backlights...

Alright i have a scan of the bottom of the pus that is supposed to be in it. Looks like the sub board is actually built into the bottom of the supply on mine on the secondary side.

The supply is relatively cheap. http://www.shopjimmy.com/lg-eay62810...pply-unit.htm# So if i cant track it down component wise on the board i might just buy a new PSU, if the LEDs check out ok.

I'll probably start my own thread on it later tonight once i get there.

**JeffJ** · 02-25-2015, 08:51 PM

Re: LG 42LE4500, Int No Backlights...

I know this The 47LN5750 is a different modle but the issue you posted is the exact one i have when i went tonight to diagnose.

the BL_ON signal is good from the main board 3.21v I get the 2 seconds to black. Putting my meter on the LED outputs i get a brief 100v thats when the backlight is on and a high pitch hum and then it drops to a solid 79.8V If i remove the LED connector and test the voltage its 150V but of course this is with no load. When the backlights are on, its perfect looking for those few seconds. You can tell its logic based (the controller ic you mention) because when you shut the tv ff you get a few seconds of perfect backlights again.

I suppose I'm safe to say the psu needs to be replaced. Or am i wrong? Shame this only made it 13 months.

**Alastair E** · 02-26-2015, 07:24 AM

Re: LG 42LE4500, Int No Backlights...

In your case with a 13 month old set--I would shout at Mr Havis Kwon the senior vice president of Entertainment div. LG UK.
I shouted at him in email for Not providing Proper service Info to the trade, preferring to restrict to LG Stealers, and the terrible quality of the service generally.

Its also a case for Sale Of Goods Act as unfit for service--you shouldn't ever have a set fault in only 13 months!

Worth a try! They also have an online chat thing--but those are fob-off merchants....

You can tell him that you've researched the web and found lots of these and similar age LG sets--with the same problem--It does seem to be a very common issue....

As that PSU is different to mine--you would need to check what pins are marked and try what I did--But there's always the risk of blowing the PSU completely!

Look for the 'ERR' pin and the 'FB' pins on that sub-board, Those are the ones to mess with, and try as I did above.....

**JeffJ** · 02-26-2015, 09:51 AM

Re: LG 42LE4500, Int No Backlights...

If this replacement board doesn't work then i will get up LG's arse about this. It's Hockey time here and not looking to argue with LG for 4-6 weeks about it being a warranty issue. Although we're not pleased. Almost bought the samsung for him. We had a good laugh about that last night. Damn lemons.

I am fairly confident with reading your results, although the design is different the symptoms are the same. That the supplys logic is just crapped out, I had a dvd with a test pattern playing on it and it wasn't a fact of the LED stips having an issue as there were no dark spots when the leds came on. BL_ON signal is good. So Power under load or logic on the led controller is my guess and was your test results.

I'll keep you posted if i have to get thermal on LG if this doesn't work lol I got a new supply pulled from a crack screen in shipping for 28 pounds, or 54 Canadian. So its not a total loss.

**RJARRRPCGP** · 02-26-2015, 07:38 PM

Re: LG 42LE4500, Int No Backlights...

Deja-vu of pre-2010 LCDs!

Like the faulty inverter transformers, CCFLs and wiring.

**Alastair E** · 03-30-2015, 12:48 PM

Re: LG 42LE4500, Int No Backlights...

And another Poxy L.G. 42LE4500 damned idiot LED PSU sub-board Controller causes troubles.
Yet Another controller to chuck over the hedge.....

This one is from Brother-in law, was apparently dead.

The larger of the two wire-ended fuses of the PSU was O/C. Checks on the PSU indicated the two MOSFETS that drive the LED SMPS Transformer were short, and a tiny hole in the controller-chip.

The similar stage that runs the 'everything else' SMPS Transformer (12V and 20V supplies to mainboard) appeared all OK, but both these supplies run from a common fuse.

New chips and MOSFETS were ordered--which came in today.

I replaced the chip and the two MOSFETS in the LED SMPS stage and also their 4.7 ohm and 100 ohm gate resistors that were also O/C. A check of the resistance across the two caps that supply the raw LED supply indicated a 400 odd ohm leak. I removed that abortion LED Controller sub-board, the short disappeared....
Hmm--No real surprise there!

I also wired the LED plug-strips to the LED Raw supply caps as I had done on the one above.

I did not refit this LED Controller due to the short, but modded the set as above.

I replaced the wired in 3.15A fuse that supplies both the LED and the 'everything' stage and fired the set up....

Still dead--but now at least we have a relay click--but not much else!
A check across the group of 4, 22uF 450V caps indicated 390V, so the PFC was running, as well as the small Standby 3.3V supply.

A check of the 'PSU-On' pin indicated 3.3v when turned on and relay clicked, then dropped to '0' when std-by button pressed again--but takes a few seconds to go to standby and relay drop out.

After lots of potching and waste time, I then replaced the Other SMPS Controller-chip that runs 'everything else' (20v and 12V rails to mainboard) and then we have life!
--Its MOSFETS and gate-resistors checked out fine so were left as is.

Again I added a resistor to increase the 72V LED supply to 85V as done above, and we all working OK--(This set had a AUO LED backlit panel designed for average of 89V LED supply, I set the supply to 85V as before using a 12K, but cant recall that first set's panel type.)

--It seems, that a fault in the LED Driver sub-board can not only kill the LED SMPS stage, it can also--as in the first set, cause intermittent backlight....

When the LED SMPS stage failed, it must of somehow spiked the rail and killed the 'everything else' controller-chip too...

Damned Fool LG Crap PSU's.....

**sordids999** · 03-30-2015, 02:19 PM

Re: LG 42LE4500, Int No Backlights...

Hi Alastair sorry to hijack this thread but i have the 47LE5300 and just wondering how i can make the psu work with out the mainboard ?
basically im not sure if the screen is good before i continue and buy another mainboard

thanks

Attached Files

**Alastair E** · 03-30-2015, 02:51 PM

Re: LG 42LE4500, Int No Backlights...

Hmm--I have no idea--Thats a Different PSU!

Do the PS-On, BL-On dodge with 1K's....

**Alastair E** · 03-30-2015, 02:56 PM

Re: LG 42LE4500, Int No Backlights...

This is the PSU I've been working on....

This picture clearly shows the DREADED GREEN TURD that is the LED Controller Sub-Board--That I totally deleted in two sets!

**sordids999** · 03-30-2015, 03:09 PM

Re: LG 42LE4500, Int No Backlights...

i have power-on but cant find bl-on
here are my legend settings

20V POWER ON
20V 20V
GND GND
GND GND
3.5V 3.5V
3.5V 3.5V
GND GND
V-SYNC GND
DRV ON 12 V
SCLK 12V
PWM DIM 12 V
ERROR OUT SIN

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LG 42LE4500, Int No Backlights...

LG 42LE4500, Int No Backlights...

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