32LG5700 LCD: Low contrast/high black level

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32LG5700 LCD: Low contrast/high black level

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flashce
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Mar 29, 2015, 9:09 AM

Post #1 of 5 (2228 views)
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32LG5700 LCD: Low contrast/high black level	Can't Post

Hi everyone,

I have an old 32" LG LCD TV, model 32LG5700, with a fault: the image output appears to be very low in contrast and/or high in black level, overall making it look washed out.
I have taken 2 pictures to illustrate the problem. The brightness was set to 40% and contrast to 50% in both pictures (the default setting). Backlight is 0% in the first and 100% in the second picture.

Backlight 0%: http://imagizer.imageshack.us/a/img538/23/Uv5PL8.jpg
Backlight 100%: http://imagizer.imageshack.us/...g912/7852/FDVFKi.jpg
The top screen is the TV and the bottom screen is a laptop that clones the display to the TV.

Adjusting the brightness, contrast and backlight settings doesn't help at all. At the 0% brightness setting, the darkest portion is still as grey as it is on 40%.
This occurs on all input ports. In fact, the OSD itself also displays the behavior so it can't be an input-related issue.

Some additional information that may help:

When powering on the TV, the image takes a couple seconds to adjust to the final state. At first, it has a very low contrast, being almost grey, and then gradually changes to what you see on the pictures within about 3 seconds.
Sometimes, however, the image appears perfect for a very short amount of time before becoming faulty again within these 3 seconds. I do not know yet what triggers this, it may be after the TV has been powered off after a longer period of time but I am not sure about this.
There is some flickering going on as well as ghosting/image persistence.
The reason I took pictures with different backlight settings: There is a slight buzzing noise when the backlight setting is set to anything but 100%. I have read elsewhere that this hints to a faulty/dying backlight inverter.

Now, I am not sure if there is actually supposed to be any backlighting at all when it's set to 0%, so could that actually be the problem here?
The image persistence seems to indicate that the panel is dying. Could that be the issue?
Or maybe it's both, or something completely different?

Thanks for your time in advance, any help is greatly appreciated!

Repair man
Enthusiast

Apr 4, 2015, 5:24 AM

Post #2 of 5 (2197 views)
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Re: [flashce] 32LG5700 LCD: Low contrast/high black level [In reply to]	Can't Post

This may be a bad Tcon board but before spending any money there are two things you can try.

1 -- remove the LVD cable from the Tcon board & clean it's contacts & reinsert it back into the tcon. The LVD cable is the flat cable that leads from the main signal board up to the Tcon board. You only need to clean the end of tha cable that connect to the tcon, the socket on the Tcon will be fine. You can clean the end of the LVD cable with some rubbing alcohol & a cotton swab being careful not to leave any cotton fibers behind. also allow the alcohol to dry before replacing cable.

2 - Check the internet (ex: youtube, google) to find how to access a service menu, I know of some ways but there are several for LG (different ones for various models) so it will be faster for you to look them up & try them until you find one that works. Once you do get in to a service mode DO NOT adjust anything you don't know or you will likely cause a bigger mess, the one thing you will be looking for in there is Factory Reset, find that & go ahead & try a factory reset. I know once in there there are settings for brightness etc but do not be temped to change these settings because there's now way to tell what they are supposed to be set at without a service manual; just look for a factory reset & that should make all necessary adjustment automatically.

If neither above method helps then you may want to try a new Tcon board. Before trying the new Tcon board let us know & someone on here can give you advice on replacing it. Just a few steps so you don't damage the delicate sockets on your new board if you decide to go that route.

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If you (or anyone reading this post) have any further questions or need clarification please feel free to contact me direct; you can find my email address by clicking on my user-name.

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(This post was edited by Repair man on Apr 4, 2015, 5:25 AM)

flashce
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Apr 4, 2015, 6:18 AM

Post #3 of 5 (2192 views)
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Re: [Repair man] 32LG5700 LCD: Low contrast/high black level [In reply to]	Can't Post

Oh nice, the forums are back.
Thanks for the reply Repair man, I have looked into the issue more in the past few days so I might as well post some updates.

I found somebody with a similar color problem on the same TV model on the Badcaps forums. The guy ended up replacing his T-Con board but he bothered to measure the voltages on almost every test point on both the good and the bad board and post the results, so I've done the same with mine to compare:

Code

#General Voltages 
#		good	bad	mine 
V12IN		12.0	12.0	12.21 
V12		12.0	12.0	12.21 
VGL		-6.0	-6.0	-5.95 
VGH		27.3	27.3	27.2 
AVDD		16.5	16.5	16.4 
VGHC		25.8	25.7	25.7 
VCOM		6.7	15.8	6.8 
VGMA_REF	15.8	16.0	16.0 
CONF		6.7	6.7	6.8 
V1D8		1.8	1.8	1.8 
VZREF1		2.5		2.4 
XSFT_M		1.3	1.3	1.3 
YV1C		2.5	2.5	2.5 
YOE_B		1.8	1.8	1.8 
YCLK_B		0.38	0.38	0.385 
YDIOU_B		0.0	0.0	0.0 
XSTB_B		0.25	0.25	0.25 
XPOL_B		1.6	1.6	1.65 
YOE_F		1.8	1.8	1.78 
YCLK_F		0.38	0.38	0.38 
YDIOU_F		0.0	0.0	0.0 
XSTB_F		0.25	0.25	0.25 
XPOL_F		1.6	1.6	1.65 
#VGAMA References 
#		good	bad	mine 
VGAMA1		15.8	16.5	15.86 
VGAMA2		15.8	16.5	15.8 
VGAMA3		10.9	16.5	10.74 
VGAMA4		10.3	16.5	10.06 
VGAMA5		9.1	16.5	8.9 
VGAMA6		8.7	16.5	8.63 
VGAMA7		8.7	16.5	8.6 
VGAMA8		6.7	3.3	0.21 
VGAMA9		6.7	3.3	0.21 
VGAMA10		6.5	3.0	0.21 
VGAMA11		5.3	1.9	0.21 
VGAMA12		4.7	1.2	0.21 
VGAMA13		0.2	15.8	0.21 
VGAMA14		0.2	16.0	0.21 
#U502 Test points 
#		good	bad	mine 
REF2		15.0	16.5	14.97 
REF3		10.9	16.5	10.73 
REF4		10.6	16.5	10.45 
REF5		10.6	16.5	10.43 
REF6		9.5	16.4	9.34 
REF_F1		15.8	15.9	15.9 
REF_F7		6.5	8.7	8.6 
REF_F8		6.7	6.8	6.75 
REF_F14		0.15	15.6	0.16 
REF9		6.2	4.5	0.21 
REF10		5.5	5.8	0.21 
REF11		4.8	7.2	0.21 
REF12		4.7	7.5	0.21 
REF13		0.9	14.8	0.21

The general voltages are all more or less fine, except maybe for V12 and V12IN which are exactly 0.21 V higher than they should be, and we have several points that show exactly 0.21 V instead of the desired voltage. I'd be surprised if that was just a coincidence, but I'm not sure.
Then there's also REF_F7 which is 8.6 V compared to the 6.5 V of the good board.

I'm sure replacing the T-Con board would fix the color issue. However, I'd like to avoid spending too much money on a 7 year-old TV which I got for free, especially since it most likely wouldn't fix the issues of image persistence and flickering. These are issues I could live with though if the fix to the color problem was somewhat inexpensive. Sadly though, most people demand ripoff prices for the board in question.

As for your suggestions:
I did try to clean the LVD cable's contacts just now as per your instruction. It didn't help though.
I also researched on how to access the service menu for this TV. It looks like you need a special service remote for LG TVs - I don't even have the regular remote to begin with.

Repair man
Enthusiast

Apr 4, 2015, 8:47 PM

Post #4 of 5 (2184 views)
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Re: [flashce] 32LG5700 LCD: Low contrast/high black level [In reply to]	Can't Post

I've gotten into service menus on LGs without special remotes.

Try toggling the Menu button over & over (menu appearing on & off) until the TV no longer responds (at this point menu may be on or off)
When the menu no longer changes press 9 8 7 6 enter.
You may now get a screen asking you for a password, try all zeros to start & if that doesn't wok you may have to go through the steps again & try different codes other than zeros.

The small difference in voltages you measured (ex: 0.21 volts) are nothing to worry about but the VGAMA 8 through 14 and the REF 9 through 14 are way off. This could be something in a service menu that could correct that if you can find a factory reset.

------------------------------------------------------------------------------------------

If you (or anyone reading this post) have any further questions or need clarification please feel free to contact me direct; you can find my email address by clicking on my user-name.

Learn Plasma TV Repair

_________________
Learn LCD TV Repair

flashce
New User

Apr 6, 2015, 8:35 PM

Post #5 of 5 (2168 views)
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Re: [Repair man] 32LG5700 LCD: Low contrast/high black level [In reply to]	Can't Post

Thanks for the tip about the service menu.
Since I don't have any kind of remote, I had to try a few other things to access it. I managed to do it though in the end.

Anyway, the factory reset didn't help. Neither did the image calibration options in the EZ ADJUST menu. Actually, the service menu doesn't have all that many settings compared to what I'm reading about these post-2009 models so it wasn't as interesting as I had hoped.

I guess the only way to fix the color issue is to fix the T-Con board itself. Preferably, I could pinpoint which component on there is causing trouble and give repairing it a shot. Then again, that might end up costing more than a replacement board, which looks like I could get my hands on for about 35 Euros. Not sure if that's worth it though considering the other issues this set has.

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