All Over White Washed Out Picture LG 42LF2510

[dicky96]

Sorry guys, I keep coming up against things that puzzle me due to only just starting flat panel TV repair


Anyway this is a LG 42LF2510 with a horrible pale low contrast washed out picture.

This is on any source or even OSD menu. From what I learned so far this is a Tcon problem.

I did a bit of googling and research and thought I may fix this one without bothering you guys again

I tried disconnecting each Tcon cable in turn to see what the other side of the screen would do. Results are with either Tcon cable disconnected I get a good picture on the other side of the screen.

With both Tcon cables connected both sides of the picture are bad. I didn't really expect that.

PSU voltages 5V, 12V, 20V are about right.

See pics

and TIA
Rich (again!)

[dskall]

Re: All Over White Washed Out Picture LG 42LF2510

Can we get some good pictures of t-con

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

Sure dskall

Pic any good?

[diif]

Re: All Over White Washed Out Picture LG 42LF2510

Sounds like the common AS15 ic failure.

[ReeceyBurger123]

Re: All Over White Washed Out Picture LG 42LF2510

Fuck sake takes 5 seconds to research and find out this is a tab bond issue whoch is very common on these. I used to like helping here now just pees me off

[dskall]

Re: All Over White Washed Out Picture LG 42LF2510

And failures on these t-cons and as-15 chips are never prone to failure
What does picture look like with a video input?

[attainteddragon]

Re: All Over White Washed Out Picture LG 42LF2510

to confirm the as15 chip. measure the test points marked vg1 through to vg22 (i think)

yours are scattered all over the board. sometimes they just try to make things awkward.

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

Will try later - today is definitely a beach day here

When measuring the test points is that with both Tcon cables connected or just one.

Because the way this is behaving would it be possible the voltages are going to be OK with either cable connected and bad with both?

[vinceroger69]

Re: All Over White Washed Out Picture LG 42LF2510

Test it with all cables connected as we need to see if the ic is putting out the wrong voltages

[chrismurphy]

Re: All Over White Washed Out Picture LG 42LF2510

Faulty T-con
Replace T-con board

[chrismurphy]

Re: All Over White Washed Out Picture LG 42LF2510

Fuck sake takes 5 seconds to research and find out this is a tab bond issue whoch is very common on these. I used to like helping here now just pees me off

You do yourself no favours by the languish or lack of respect ,grow up

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

Faulty T-con
Replace T-con board

Can't I fix the Tcon board?

@vincerogers
Voltages as requested. I couldn't find all test points VG1 - VG22 but I found 14 of them and the AS15 says it is 14+1 channel so I hope I got them all.

For my own interest I did take voltages with both T-con cables and then with just one connected. Actually there was very little difference, which doesn't explain to me why I get a good picture on either half screen.

The first voltage is with both cables attached.

VG1 - 15.23 - 15.25
VG2 - 15.60 - 15.69
VG4 - 12.72 - 12.71
VG6 - 10.82 - 10.84
VG8 - 9.73 - 9.66
VG10 - 8.06 - 8.04
VG11 - 7.88 - 7.88
VG12 - 7.28 - 7.23
VG13 - 7.12 - 7.14
VG15 - 5.15 - 5.16
VG17 - 4.14 - 4.13
VG19 - 2.79 - 2.78
VG21 - 0.686 - 0.659
VG22 - 0.308 - 0.308

I don't know what I should see, but VG1 stands out as not following the sequence of the other voltages, like it should be higher. So I had a look at AS15 schematic and see that VDD is 18V max.

I noticed there are three buck regulators on the Tcon board and spotted a test point marked 22AVDD right next to one of the buck regulator coils so I checked with my DMM and see that pin 7 AS15 (Vss) is connected to 0V and pin 8 (Vdd) goes direct to this test point. So it is running on a single supply rail.

So following a hunch I checked the voltage at 22AVDD and found it is 15.83V.

If I understand the AS15 datasheet properly the outputs can only go to the supply rail voltage, so am I on the right track here?

I'm wondering if VG1 is too low... because the supply to AS15 Vdd is too low.

It's just a thought, I didn't even know about Gamma Voltages until this thread. I'm just working on basic troubleshooting principles

Rich

[vinceroger69]

Re: All Over White Washed Out Picture LG 42LF2510

there is a excel spread sheet in tom66 thread if you put your voltage readings in it will tell you pass or fail
https://www.badcaps.net/forum/showth...gamma+voltages

[attainteddragon]

Re: All Over White Washed Out Picture LG 42LF2510

vg1 is lower than vg2.

instant fail. the voltages should be rather linear.

time to change out yous as15 chip.

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

vg1 is lower than vg2.

instant fail. the voltages should be rather linear.

time to change out yous as15 chip.

VG1 being lower than VG2 is what I thought is odd. But before I order parts to change AS15 chip, does anyone know what voltage rails I should see from the buck regulators on Tcon board?

Because Vdd to AS15 is reading 15.83V at test point 22AVDD - and from what I understand of the datasheet that would prevent VG1 output being higher.

VG1 is exactly 600mV below Vdd. 15.83V seems an odd supply voltage,

Rich

[attainteddragon]

Re: All Over White Washed Out Picture LG 42LF2510

according to my notes, vdd is ok if between 15 and 18v. that is in general, not this exact t-con.

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

I've ordered a few AS15 as they seem useful things to keep in stock

The test point is not marked 22AVDD that is my error because R122 was next to it. The test point is marked AVDD

I probed around the board a bit more. VG1 is No (pin 48 AS15) VG2 is Mo (pin 1 AS15)

Looking at the corresponding inputs Ni and Mi (pins 38 and 37 respectively) the voltages on the inputs are the opposite way around with Mi being lower than Ni.

In fact the voltage on Ni corresponds to the output on VG1 - 15.25V but the voltage on Mi is lower than Mo (VG2)

So maybe actually it is not that VG1 is too low but that VG2 is too high - Vdd minus 0.6V exactly which also sounds a bit omenous.

This gets around the obvious fact which was bothering me - VG1 can't be higher than Vdd!

It sounds more like I proved the AS15 is the problem now and not the supply rail. At least to my mind. Put this one on one side as well waiting parts in about a week.

Hmm something interesting next on the bench - vintage 1980s Onkyo Amplifier

Rich

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

OK, replacement AS15 fitted - and that fixed the washed out fault.

Incidentally I managed to get a solder bridge causing a short between Vdd and Vss but after soldering the bloody fiddly AS15 I proceeded to check continuity between each pin and the pad, and also for shorts between any adjacent pins.

So I found and fixed the problem before fitting the T-con bard and powering up.

The solder bridge had gotten between the two pins behind the 'dog leg' where the pins go up to the chip housing and was very hard to see even with x20 jewellers loop until I got the board at the right angle to look up there.

At first I though this would be impossible to clear and I would have to replace the AS15 again, but a couple of attempts with plenty of liquid flux and some solder bread got it sorted. There is still a little bit of solder up behind there but the short is gone.

So power it all up - and replacing AS15 has fixed the brightness fault... Yippee

But I must be really quite unlucky as I now have another problem. With the TV mostly reassembled and upright I have a vertical green line down the screen when displaying the OSD menu. It's not there on the black area of the screen so I didn't see it with the set face down on my bench, I am hoping that is a dirty contact on the Tcon cable?

I also have an area of the screen centre right that is menu background is dimmer than the rest of the menu.

And this really weird looking thing going on where, if you let the LG 'no signal' screen saver wander around the screen, once it reaches near the bottom right of the screen it starts leaving ghost images behind which fade away, and the closer the corner it gets the longer the ghost takes to fade - but once it moves away from this area it just steps around the screen normally. See video as it shows the problems better than I can explain

https://www.youtube.com/edit?o=U&video_id=dn8KmIV3_bA

So as usual I am

Rich

[vinceroger69]

Re: All Over White Washed Out Picture LG 42LF2510

The video link dosnt work?

[dicky96]

Re: All Over White Washed Out Picture LG 42LF2510

Sorry
https://youtu.be/dn8KmIV3_bA