LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter scenes

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

No need to re-test PSU, and you can check that fuse voltage on the V=20 range (not 200) to get more digits.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Cleaning results:
No change.
(Unfortunately, the only ribbon ends I couldn't clean are the pair seen to disappear in the top of this pic.
.
It would require alot more dismantling in order to gain enough access to release/refasten the catches safely).

F1 fuse test results:
Left side = 11.95 to 11.97. Jumps to 12.15 during blink.
Right side = 11.94 to 11.95. Jumps to 12.13 during blink.

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

This seems like a t-con fault (the board you tested the 12V on), as the voltage goes up, it indicates it draws -less- power.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Thanks Tom,

So just to confirm - it is based on my results from earlier, in your opinion, that the biggest suspect is the power board (t-con), and the spike (drain) detected on the 20v?

Results:
8/7 - 5v = 5.2, no change during blink
10/9 - 5v = 5.2, no change during blink
14/13 - 12v = 12.3, no change during blink
18/17 - 20v = 21.1 to 21.2, jumps to 21.3 during blink


I have sourced a new power board for this rare TV at £130 a pop and 2-3 week delivery time, but I'm happy to spend that if it's very likely to fix it.

Let me know if you think I should give anything else a try before parting with my cash

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

No, I suspect the T-con. The PSU is fine, the slight voltage change is probably OK.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Right, derp - so that board is the T-con, and 12v was read off the F1 fuse. Gotcha.

That's good news, replacement T-con (p/n 6870C-4100D) is more readily available than PSU and AV boards, at only £20 second hand - I'll order one and report back.

Can't thank you enough man. Selldoor too. T-con arrives Thursday, I'll post back.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Hi Tom and all, hope youre well. Any chance you are online?

I installed the new T-con a few moments ago. No change. How utterly gutting.

Any thoughts on my next move? I'm pretty desperate to fix this mother asap, by any means necessary.

A reminder of the PSU results, and the slight drain detected on one pin:

PSU Results:
8/7 - 5v = 5.2, no change during blink
10/9 - 5v = 5.2, no change during blink
14/13 - 12v = 12.3, no change during blink
18/17 - 20v = 21.1 to 21.2, jumps to 21.3 during blink

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

The change in the 20V is so very slight, and unlikely to be significant.

Have you tried heating the AV board with a hairdryer in case it gets worse with heat?

My next suspect would be the AV board unfortunately...

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Hello.
Ah well, at least the AV board is available. Even at £130 ill be happy if it works.

Regarding heat, certainly the problem only occurs after te TV has been on for a few mins.

Also the time between blinks is precisely the same each time around. I have previously sat there with a lap timer and measured 3.9s, 3.9s, 3.9s etc..
On another occasion it will be 8.0s. Seems odd.

Heat test in progress..

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

YES, Tom. Success. Heat does appear to aggravate the problem.
On a file that normally threw up 3 or 4 blinks, I just clocked a dozen when pointing an electric heater a small distance from the AV board.

I'd like to think this makes it almost definitely the AV board, but is there anything else I should try before chucking £130 at the problem?
(The board between the AV and T-con, for example, would also have got quite warm during the test)

And I am guessing there's no AV board tweaking I can do for a temp fix in the meantime?

Lastly, do you happen to know of any LCD part retailers who might have a 2nd hand board in stock?
I have sourced the part new, but its £130 and a 3 week wait. Have also tried calling around, eBay, EMOS, and Reclaim247.

Sorry for all the queries, thank you.

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

There is a quick fix you can do if you want to get the TV to last a few months. It is known as a reflow. Used to repair Xbox 360 / PS3 consoles. It is worth a shot. The most common technique is about 2 minutes in the oven at 230C to allow the solder to reflow. If heat is causing a problem, it is most likely a BGA failure (which reflows can fix); this is due to the use of lead-free solder, which is unreliable compared to leaded stuff.

I use flattvparts occasionally, and eBay for the rest. Also, are you using the "EAXnnnnnnn" number, or just your TV model? Check around the local area for similar TVs with smashed screens -- boards may be harvested.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Yeah, I've been searching both 'eax62109301', and 'LD920'.
Thanks for flattvparts - theyre oos too unfortunately. A rare TV, this one. LG pulled it from retail after 2 months to sell exclusively to hotels, and replaced it with the LD950. Making that that £130 call to LG now!

Oven sounds dangerously tempting. Since I have a smaller backup TV, I'm blatantly going to do it, immediately.

So, I've preheated oven to 230c. Should I place it inside with tall screws on the corners to keep the board from touching anything (upside down so solder is on top?) , and leave it in for exactly 2mins, before it turns golden brown?

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Board facing upwards, main processors pointing upwards.
230C is best, it is the commercially used reflow temperature. 250C may be too high.

2 minutes maximum, some people have experienced warping at 5 minutes and melted puddles at 30 minutes.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

lol; 30 minutes.

230C, board upwards, 120 seconds. Noted.

Christmas cooking take 1. Here goes nothing..

[selldoor]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Suspense is killing me - got the marzipan and icing ready?

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Hi selldoor,

Tom's recipe was an exciting one, so I'm gutted to report that it didn't work!

But as a Christmas consolation prize, the only further damage caused was to my vocal chords. My 'new' second hand TV has been the light at the end of the tunnel of a hectic and mammoth house refurbishment, which I need to complete in the next couple of days. The live crash course in diagnosis and repair has been incredibly useful - but I've set myself back a few days with the refurb, and the stress has been gradually mounting.

Basically, when the TV blinked again a few moments ago it was the straw that broke the camels back, and I let out an anguished inhuman roar, loud enough to scare the noisy kids next door into silence. Perhaps you heard me.

10 minutes later and things are much calmer It won't arrive until mid January, but I've got the replacement AV board on order with option to cancel if I find a second hand one sooner.

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Hi guys,

Happy new year to you.

I guess the AV board isn't the problem. My replacement arrived today. I installed it just now. The problem remains.

So far I've purchased replacement T-con and AV board.

Any ideas?

Yours,

Depressed.

[selldoor]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Well - Happy new year - as you have replaced both boards all I can come up with quickly is that you should try and dismantle further to get at the other end of the ribbon cables.
Thing is I dont know if when you get there they are the sort you can take out and clean or
if they are permanently attached. At least it will be one possible problem less. Its been an
expensive new hobby for you so far

[tom66]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

I am almost considering perhaps a software problem?
How does changing things like the brightness settings affect the problem?
Does LG have a firmware update available?

[Stimpers]

Re: LG 47LD920 Display (not backlight) blinks off every 8 seconds during brighter sce

Hi Tom, Selldoor, sorry for the delay and thanks for responding.
I needed to work on other stuff for a few days, but I'm back.
I've come too far to give up now!

Apologies for the long message, I've been running a few tests and have info I think will be useful.

I previously thought that brightness/frame complexity were affecting blinks. Well, it doesn't. It's colour.
I took a screenshot during a troublesome scene, and by playing around was able to ascertain the following:

• [1] Blinking never occurs when colour is turned down to zero.
  As soon as I nudge colour on at all, even at 1%, the blinking starts again.
  
  [2] Blinking always occurs during frames which contain a mixture of colours.
  
  [3] Blinking never occurs on a screen saturated with one colour;
  blue, red or green, black or white. Even with brightness etc maxed.
  
  [4] By moving a troublesome colourful screenshot partially off screen in any direction, against a plain background, I can completely prevent the blinking.
  
  [5] Pauses between blinks are identical. However, the pause can be made to vary depending on how high the colour setting is cranked. eg,
  -At 1% colour, blink frequency = Every 7.8s precisely
  -At 100% colour, blink frequency = Every 4.8s precisely
  -Blinks continue at this frequency as colour is turned down, but stop immediately at 0% colour
  
  [6] When blinking occurs, the OSD menu disappears too. But the plain grey menu can be enough to prevent a blink occurring.
  
  [7] A portable heater pointed at the AV board previously led us to believe that the AV board was at fault, as it appeared to increase blink frequency.
  However, I am now thinking that I was either
  a) wrong about the freq increase, or
  b) that the heater was affecting another component.
  
  The TV is currently remounted, but I will take it down again tomorrow and run heat tests on other areas. I will also take the opportunity to check all connections, including the two recessed T-con ribbons which I couldn't reach last time.

In the meantime - what do you think? Tell me I'm not running out of 'next steps'.

See attached photos of scenarios described.
thumbs up = working
thumbs down = blinking

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