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Equipment Repairs => LCD TV forum => Topic started by: samisat on September 29, 2015,09:30:37

Title: LG 47ln578v
Post by: samisat on September 29, 2015,09:30:37

Hi,when I plug the tv in back light will come on for 1 second then goes off ,no light, no sound.thanks for your time.

Title: Re: LG 47ln578v
Post by: jordan on September 29, 2015,09:36:18

Check LEDs in LCD display panel

Title: Re: LG 47ln578v
Post by: downunder on September 30, 2015,05:58:01

Hi Sam,

If you strip the panel to expose the backlight LEDs, and remove to white sheet covering the LED strips,
you'll find each strip is extended by tacking another strip to its end, so as to make one longer strip out of two strip. It's the join that often gives trouble. You can solder a jumper across the connector to bypass it.
Remember, the LEDs in each strip are in series, with the last LED having a return path back to the pcb on the side where all the strips are configured.

Bruce

Title: Re: LG 47ln578v
Post by: chappers on October 30, 2015,15:40:18

Hi, same set and same problem.

To save me time, can someone please explain the method to strip the panel for access to the LED strips?

Thanks

Title: Re: LG 47ln578v
Post by: downunder on November 02, 2015,05:36:33

This video should give you the gist of it.

https://m.youtube.com/watch?v=Bf5T2wwtydY

Title: Re: LG 47ln578v
Post by: Southerner1959 on November 04, 2015,05:40:45

I have the same Backlight fault on an LG set . . .

The power to the LED strips from the PSU Board is only on for the short time the screen is on.

What I don't understand is HOW the screen can work perfectly for  about half a second on switch on, and again at switch off, if the LED strip is faulty?

Having said that, what would be the normal resistance measured using an Analogue ohm-meter of the LED strip?

(It looks a really difficult job to take the screen apart, so I'm trying to make sure this is the problem)

Title: Re: LG 47ln578v
Post by: kennyc on December 15, 2015,05:05:13

Hi guys ,have had same problem with the 40 inch Toshibas . Never managed to get to the bottom of any of them . Strips are glued on . To be honest dont think they are designed to be fixed . They want customer to throw TV away and buy new one just like a kettle every couple of years . We all better start looking for other jobs

Title: Re: LG 47ln578v
Post by: zomikula on December 15, 2015,09:00:28

Use a heat gun at around 200 to heat up the strips loosens the tape and they come off
Same to reapply
heat up the adhesive and when applying heat and push down.

If replacing single led this can be done insitu without removing the strip

Title: Re: LG 47ln578v
Post by: Turnip on March 11, 2017,12:39:11

Hi Folks,

Just had one in where 2 Leds were S/C and one O/C. Replaced them and powered up with a bench supply finding all strings lit OK.

Reassembled without breaking the screen - Powered up, and after a brief screen flash it cut to S/by.

Powered up again - Straight to S/by. Checked Leds for a possible chassis leak - Nope. Disconnected feed to Leds - Cuts to S/by.

Bit puzzled - Any thoughts ? - Chris.

Title: Re: LG 47ln578v
Post by: tv tony on March 12, 2017,15:24:54

Have this range of sets on the bench all day Chris. LED failure doesn't invoke stand/by.

Title: Re: LG 47ln578v
Post by: bonesy on March 14, 2017,05:03:01

Hi Turnip,I might be talking out of my hat,but check that the electrolytics in the output for the LEDS,If the set has been laid on its back (panels to bench)the caps break away from PCB very easily,I've done it a couple of times,I think then set goes to st-by.Just a thought.

Title: Re: LG 47ln578v
Post by: bonesy on March 14, 2017,05:05:01

Hi TV Tony,I know you repair a lot of LG products,just curious,do you change the strips,or replace the LEDS?

Title: Re: LG 47ln578v
Post by: tv tony on March 14, 2017,09:35:05

Hello,
              I change the leds, using a leister hot air gun, you just have to be careful to align the lenses afterwards, 80% success rate 1st time, the amount of leds on each stick are staggered but I use a redundant laptop psu (19v) After splitting the strips. Obviously the sticks with 5 lamps on each stick will be dimmer. They can go s\c or o\c, the hardest part isn't replacing the lights, it's re-aligning the lenses. If you want the address for obtaining the leds I'll dig it out. They come in rolls of 1000 but cost peanuts.

Title: Re: LG 47ln578v
Post by: tv tony on March 14, 2017,09:38:04

Just seen how much you pay for lamps Bonesy, a thousand for around £18.00, I'll find you the address.

Title: Re: LG 47ln578v
Post by: bonesy on March 14, 2017,10:22:10

Yes please Tony.To start with I replaced all the strips,not cheap,but 100% no come backs.But I've started replacing LEDs then testing LED strip for brightness & overall even brightness,but the first two I fixed around two months ago by looks of it are coming back,LEDS failed again!Do you replace just the failed LEDS or all the LEDS on the strip?Also what do you use to refix the lens.I've been using a gel type super glue,which seems to work o.k.,some use clear silicon rubber.

Title: Re: LG 47ln578v
Post by: vinceroger69 on March 14, 2017,11:58:37

what glue are you guys using for the lens replacement i have tried a few but what seems the best?

Title: Re: LG 47ln578v
Post by: jordan on March 15, 2017,01:57:37

http://tinyurl.com/jkgh9zk

Title: Re: LG 47ln578v
Post by: vinceroger69 on March 15, 2017,04:38:14

Quote from: jordan on March 15, 2017,01:57:37

http://tinyurl.com/jkgh9zk

Thanks jordan for that link also what glue does everyone use for sticking the diffuser down that goes over the replacement leds

Title: Re: LG 47ln578v
Post by: zomikula on March 17, 2017,19:21:46

Using superglue gel at moment, seems to be ok.
Loctite Powerflex Super Glue Gel

Which leds is everyone using.

Title: Re: LG 47ln578v
Post by: vinceroger69 on March 18, 2017,08:06:37

Quote from: zomikula on March 17, 2017,19:21:46

Using superglue gel at moment, seems to be ok.
Loctite Powerflex Super Glue Gel

Which leds is everyone using.

Thanks thats the same glue i was using for leds ive been advised these are good sellers
http://www.ebay.co.uk/sch/proman28/m.html?item=331979775700&ssPageName=STRK%3AMEBIDX%3AIT&rt=nc&_trksid=p2047675.l2562
http://www.ebay.co.uk/itm/252450138118?_trksid=p2055119.m1438.l2649&var=551312847435&ssPageName=STRK%3AMEBIDX%3AIT
https://ru.aliexpress.com/item/100pcs-lot-LATWT470RELZK-3528-led-backlight/32456586092.html?spm=2114.03010208.3.2.uk9eB4&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10130_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10140_10055_10054_10059_10099_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10084_10117_10083_10119_10080_10082_10081_10110_10111_10112_10113_10114_130_10078_10079_10073_10070_10122_10123_10120_10127_10124_10125-10120,searchweb201603_6,afswitch_1_afChannel,ppcSwitch_3,single_sort_0_default&btsid=f9ec6b04-7456-4567-9990-6fca8d988227&algo_expid=f50ca8f3-b007-4d30-aa70-4f31a429dfa9-0&algo_pvid=f50ca8f3-b007-4d30-aa70-4f31a429dfa9

Title: Re: LG 47ln578v
Post by: zomikula on March 19, 2017,08:31:10

any one buy them off aliexpress and have some feedback

bit pricey on ebay.

Title: Re: LG 47ln578v
Post by: Turnip on March 19, 2017,09:24:29

Hi folks,

Had the feeling after fixing the first one with standard super glue that lenses might well fall off so did the next one with Bostic water based glue which stays a bit flexible.

However, as such glue is a maybe slightly conductive and might cause strip to panel leaks if it wanders about, now use super glue gel - Chris.

Title: Re: LG 47ln578v
Post by: vinceroger69 on March 19, 2017,12:55:08

Quote from: zomikula on March 19, 2017,08:31:10

any one buy them off aliexpress and have some feedback

bit pricey on ebay.

A few of us on badcaps.net have ordered these
https://ru.aliexpress.com/item/100pcs-lot-LATWT470RELZK-3528-led-backlight/32456586092.html?spm=2114.03010208.3.2.uk9eB4&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10130_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10140_10055_10054_10059_10099_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10084_10117_10083_10119_10080_10082_10081_10110_10111_10112_10113_10114_130_10078_10079_10073_10070_10122_10123_10120_10127_10124_10125-10120,searchweb201603_6,afswitch_1_afChannel,ppcSwitch_3,single_sort_0_default&btsid=f9ec6b04-7456-4567-9990-6fca8d988227&algo_expid=f50ca8f3-b007-4d30-aa70-4f31a429dfa9-0&algo_pvid=f50ca8f3-b007-4d30-aa70-4f31a429dfa9
And at the moment no ones had any failed as far as i know of.