LG 32" 32LG50FD whitish picture

[mohhingman]

Hello All,

I got a 32" LG LCD which has a colour problem.

The image is mostly white, but if brightness is maxed you can make out some of the image. Parts of the image persistently stay on the screen. There are some green and pink tints in some of the images. There are no borders, double images, vertical or horizontal lines. The image just has whacked colour.

I have tried spraying the screen borders with freezy spray - no change.

I have tried using a heat gun and freezy spray on the tcon board, power supply and also mainboard - no change.

The power supply looks good - no bulging caps, no sign of burning components.

All inputs sources and the menu have the same colour effect.

Any pointers what i can check on the boards or what to replace?

Thanks in advance

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

This is a photo of the colour problem.

[tom66]

Re: LG 32" 32LG50FD whitish picture

Probably T-con -> low VGH/VGL voltage could be caused by a bad T-con and would cause similar effect. Who makes the LCD panel in this TV, is it an LG?

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Probably T-con -> low VGH/VGL voltage could be caused by a bad T-con and would cause similar effect. Who makes the LCD panel in this TV, is it an LG?

Thanks for your reply Tom66.

It's an AU Optronics T315HW01 screen, with a T315HW01 V0 T-Con board.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Thanks for your reply Tom66.

It's an AU Optronics T315HW01 screen, with a T315HW01 V0 T-Con board.

Hi tom66, i did a voltage measurement of VGH and VGL pads on the tcon board, VGH=27V, VGL=-6.0V

cheers
Mark

[tom66]

Re: LG 32" 32LG50FD whitish picture

Hi tom66, i did a voltage measurement of VGH and VGL pads on the tcon board, VGH=27V, VGL=-6.0V

cheers
Mark

VGH seems way too high... it's usually around 10-15V. Not sure about VGL. Right now I would suggest you see if the T-con is available cheap somewhere, as AUO are in lots of cheap TVs.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Thanks a lot tom66, i'l get my hand on a new t-con board. Thanks for putting me in the right direction I'l post results once the new board is obtained and fitted.

[budm]

Re: LG 32" 32LG50FD whitish picture

I did see 27v Vgh on some panels that use TI chip.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Ah i see, thanks for that budm. This T-con board uses the TI 65161. By examining the feedback resistor values I imagine the correct voltages can be ascertained. Say the voltages went too high, would it damage the panel itself? One of the application notes in the 65161 datasheet has a VGH of 27.5V, VGL of -6V and a VS of 16V, which matches the readings on the T-con board. If the voltages are within spec, is there another thing to check on the T-con board or could the panel be damaged? Cheers

[budm]

Re: LG 32" 32LG50FD whitish picture

The Vgh, Vgl, Vs are fed to the ICs on the side Tabs on the flexible circuit board which will drive the Gate of the TFTs on the LCD panel. I cannot tell you for sure if it is still T-CON or the panel itself.

[crtfool]

Re: LG 32" 32LG50FD whitish picture

I repair a lot of LCD computer monitors, and I see this exact problem on the monitors with AU Optronics LCD assemblies. I even see it on brand new monitors right out of the sealed box. Since computer monitors have the T-Con boards ribbon fused to the LCD panel, it is impossible to tell which is at fault. I just swap out the complete LCD assembly and everything is good. It seems that this is a common fault with AU Optronics.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

I repair a lot of LCD computer monitors, and I see this exact problem on the monitors with AU Optronics LCD assemblies. I even see it on brand new monitors right out of the sealed box. Since computer monitors have the T-Con boards ribbon fused to the LCD panel, it is impossible to tell which is at fault. I just swap out the complete LCD assembly and everything is good. It seems that this is a common fault with AU Optronics.

Thanks for your input crtfool. I plan to keep testing this set of boards until I determine if it's panel or tcon. I did a search and stumbled across a great resource for LG LCD tvs. Albeit it's a different a model but it may be a good starting point for checking voltages.

http://www.scribd.com/doc/78050578/2...LK450-Training

I'm now inspecting the TCON board closely for voltage problems.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture FIXED

OK, great news on the 32LG50FD LCD set which had a white picture. It has been fixed with a replacement of the T-con board. I would like to thank all those who posted here giving me advice on where to start. A picture is shown with the replacement T-con board fitted and running a test source on the screen. This was a 2nd hand part from an internet vendor.

So for those running AUO screens which have gone white, it is due to a bad T-con board. I am lead to beleive the problem is in the LCD bias voltage generation circuitry. It had become hot on my previous board and had made scorch marks on the rear of the T-con board.

Before removing the old T-Con board I made notes of voltages on every test point. I will now re-test the voltages on this good working board and publish the results here shortly.

Regards
mohhingman

[tom66]

Re: LG 32" 32LG50FD whitish picture

Great - Another TV saved from landfill.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Hello All,

The voltage readings from the good T-Con board have been measured. A picture is attached of the board's voltage generation circuitry. It's a AUO T315HW01 V0. Different voltages in bold.

General Voltages - Good, Bad

V12IN: 12.0, 12.0
V12: 12.0, 12.0
VGL: -6.0, -6.0
VGH: 27.3,27.3
AVDD: 16.5,16.5
VGHC: 25.8,25.7
VCOM: 6.7,15.8
VGMA_REF: 15.8, 16.0
CONF: 6.7,6.7
VIDE:1.8,1.8
V2REF:2.5
XSFT_M:1.3,1.3
YUIC:2.5,2.5
YOE_B: 1.8,1.8
YCLR_B: 0.38,0.38
YDIOU_B: 0.0,0.0
XSTB_B: 0.25,0.25
YPOL_B:1.6,1.6
YOE_F:1.8,1.8
YCLR_F:0.38,0.38
YDIOU_F:0.0,0.0
XSTB_F:0.25,0.25
YPOL_F:1.6,1.6


VGAMA References - Good, Bad

VGAMA1: 15.8,16.5
VGAMA2: 15.8,16.5
VGAMA3: 10.9,16.5
VGAMA4: 10.3,16.5
VGAMA5: 9.1,16.5
VGAMA6: 8.7,16.5
VGAMA7: 8.7,16.5
VGAMA8: 6.7,3.3
VGAMA9: 6.7,3.3
VGAMA10: 6.5,3.0
VGAMA11: 5.3,1.9
VGAMA12: 4.7,1.2
VGAMA13: 0.2,15.8
VGAMA14: 0.2,16.0

U502 Test points - Good, Bad

REF2: 15.0,16.5
REF3: 10.9,16.5
REF4: 10.6,16.5
REF5: 10.6,16.5
REF6: 9.5,16.4
REF_F1: 15.8,15.9
REF_F7: 6.5,8.7
REF_F8: 6.7,6.8
REF_F14: 0.15, 15.6
REF9: 6.2,4.5
REF10: 5.5,5.8
REF11: 4.8,7.2
REF12: 4.7,7.5
REF13: 0.9, 14.8

What can be seen here is U502 is bad. On my bad board it has been so hot that the chip ID is burned off the face of the chip. It looks like it's a multiple output linear regulator IC.

The VGAMA references are totally different, which I beleive are derived from U502. The main regulator, U201 which seems to feed U502 seems to have survived with the main VGL, VGH and AVDD voltages intact, though it's running a little hot evidenced by the hot marks on the rear of the board.

The conclusion is thus, U502 is faulty and should be replaced. Since this is a chip made by AUO itself, maybe it will be difficult to source. Can anyone else chime in here? Anyone know the part number of this chip?

According to the LG 37LK450 service manual, a similar IC on the T-Con board, IC U601 is a “DC-to-DC converter which enerates the voltages necessary for the panel to operate." It is however a 32 pin beast as compared to the 48 pin chip on this T-Con board. It has a similar style of voltages on the test pads according to the manual. I posted a link to this manual further up.

Thank you all for your input and hope this post helps someone else out. Also welcome for discussion.

Cheers
Mohhingman

[tom66]

Re: LG 32" 32LG50FD whitish picture

U502 is a gamma voltage generator, something like this part: http://www.maxim-ic.com/datasheet/index.mvp/id/5757

It shouldn't get hot, I'd guess they are using cheaper chips or running them above spec.

[mohhingman]

Re: LG 32" 32LG50FD whitish picture

Thanks for your reply tom66, after looking at U502 under a microscope I can just make out it's part number. It's an E-CMOS AS15-F, a 14 channel reference voltage buffer. According the application note this chip buffers a bunch of resistive divided references. This is good news; it might be easier to source than an AUO chip and it might just be a resistor on the string of referernce inputs which is open or shorted. A picture is attached of the typical application circuit.

[killroys2001@yahoo.com.au]

Re: LG 32" 32LG50FD whitish picture FIXED

Hi There

I am facing the exact same problem and I have the exact LG LCD model as yours - 32LG50FD-AD. I don't know much about voltages, T-CONs etc..so I was wondering if you could tell me what TCON model no. you purchased and from where and I believe this will sort my problem as well. I'll try to install this myself once I figure out (via the web), where does this TCON fits.

Thanks in advance
Cheers
PK

OK, great news on the 32LG50FD LCD set which had a white picture. It has been fixed with a replacement of the T-con board. I would like to thank all those who posted here giving me advice on where to start. A picture is shown with the replacement T-con board fitted and running a test source on the screen. This was a 2nd hand part from an internet vendor.

So for those running AUO screens which have gone white, it is due to a bad T-con board. I am lead to beleive the problem is in the LCD bias voltage generation circuitry. It had become hot on my previous board and had made scorch marks on the rear of the T-con board.

Before removing the old T-Con board I made notes of voltages on every test point. I will now re-test the voltages on this good working board and publish the results here shortly.

Regards
mohhingman

[budm]

Re: LG 32" 32LG50FD whitish picture

Please provide the pictures of the T-CON board, you need the P/N as printed on the barcode and then go to shopjimmy.com to see what they have and any sub you can use.
Same model TV can use more than one supplier of the LCD panel so you need to get the correct one for what you have.

[saddle_au]

Re: LG 32" 32LG50FD whitish picture

Replacement gama chip is required. The AS15-F has failed and one or more of the outputs is pulling the entire divider chain high.

Be careful, this chip is very hard to desolder without destroying the pads. It may also be soldered underneath the chip itself.

If your interested, this is what I do to get it off and a new one on.

==========================

I have tried QuikChip for this, but it doesn't cope well with chips soldered by thermal pads underneath. I've replaced around thirty AS15s doing the following.

First, run a thick line of solder on all of the pads on all four sides so that all pins are stuck together in four strong solid masses. Sometimes it's easier to solder a wire along the pins (from the caps you just replaced in the PSupply maybe).

Second cut the pins just on the edge of the chip by running a sharp blade along the pin plastic junction. You need to run the blade towards you and almost to the bottom edge (don't go further, you may pull the blade off the chip and cut tracks on the PCB). Turn it around and attack from the other direction. Do this until you cannot feel the blade jumping on pins. I'm going to try the next one with a dremel to see if it's quicker, but it maybe too brutal.

Do all four sides and carefully remove the solder with wick. Never run the wick along the chip, always start at the chip and move it away from the plastic. You don't want to remove pads. The chip legs should fall away.

Third, if the chip still sits there still stuck on the board with no legs (about half of the AUO boards do not solder the thermal pad), either heat the chip (hard to do without temperature controlled air tools), or just physically pry it off. The chip normally splits in half like a sandwich and the bottom half stuck down is a pad of copper which is able to be peeled from the board.

Fourth, clean the board with wick to make it dead flat. Again don't go across pads, work from the centre out, or use more of a dabbing motion. You will find it exceedingly difficult to repair missing pads.

Flux the board and resolder the chip using whatever method you like, but be careful, the legs are exceedingly close together and shorts behind the legs (under them between the pads and the chip) are easy to do and wick will not get them out). I solder to adjacent legs on one side first during alignment. If you do just one, again you could remove the pad. Then I run the iron around the board using fine solder dabbing it towards the chip not along the chip.

Inspect with a microscope (cheap digital usb one) or with magnifying goggles and multimeter. On one side of the chip (clockwise from pin 1) several pins are shorted for power.

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If you have removed a pad (oops), run some replacement wire wrap wire on the board from the next component on the track to where the pad was before putting the chip on. Strip the end of the wire where the pad would have been. Raise that leg of the chip up slightly before soldering the chip down so it sits on the wire. Solder it down last.

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