Viewsonic VX2260WM LCD grey screen with lines

[doorzon]

Hi all,

I'm trying to repair two Viewsonic VX2260WM CFL LCD monitors, but no luck so far.
The CFLs light up nicely, but the screen stays grey with vertical lines (see attachment).
and the expected voltages (23V, 5V, 3.3V, 1.2V) are all in the correct locations as shown in the service manual found on the internet.

There is 5V on VLCD on the TCON board, so all simple things look ok.
Did any of you see this before? Any pointers welcome.

doorzon

[1supertech]

Re: Viewsonic VX2260WM LCD grey screen with lines

Bad screen

[momaka]

Re: Viewsonic VX2260WM LCD grey screen with lines

Post some pictures of the T-con and power supply.

I've seen this type of problem caused both by bad caps in the power supply (thought, they did appear fine on the outside) and bad voltages on the t-con.

The T-con usually has several voltages: 3.3V/5V input, 3.3V/2.5V/1.8V for the driver controller, a boosted rail of about 10-18V, TFT "HIGH" drive 15-35V, TFT "LOW" drive -5 to -15V.

There are usually test points on the T-con, so I will give you more details when you post pictures of it and the power supply.

[ReeceyBurger123]

Re: Viewsonic VX2260WM LCD grey screen with lines

Also possibly tab bond fault which is what I recon it is.

[doorzon]

Re: Viewsonic VX2260WM LCD grey screen with lines

Hi all,

thanks for the replies. I've uploaded some photos of the power PCB, LCD and TCON.

thanks,
doorzon

[doorzon]

Re: Viewsonic VX2260WM LCD grey screen with lines

Had a bit more time to do some measuring on the TCON board.

Since I have two monitors with the same symptoms, I swapped the electronics with the LCDs. The other LCD shows some information from the video input and also shows the OSD, however the response of the OSD or changes to the video input take 5 to 10 seconds to display. Brightness is also way too high, but adjusting it in the OSD does not really change a lot. Adjusting the VR on the TCON can only make it more bright.

Voltages are the same on both LCD TCONs:
VDDG 21.0V
VDDA 21.9V
VEEG -7.0V
VDDD, VDDD_P 3.3V
OE1 1.0V
VCOM_1 5.1V
STV1 0V
VDDG_FLK 17.2V
STH_F1 0V
XDON1 3.0V
FD18 1.64V
LP1 0.16V

VR1 12.4
VR2 11.8
VR3 9.9
VR4 9.3
VR5 8.9
VR6 8.2
VR7 7.3
VR8 6.3
VR9 5.3
VR10 4.4
VR11 3.8
VR12 3.2
VR13 1.0
VR14 0.3


Checked the flat-cable assembly of both monitors, all pins connect end to end.

At the moment I cannot measure the voltages on the signal board while connected to the LCD. Will solder some wires in place later to test the 5V/3,3V/1.2V when connected.

greets,
Doorzon

[momaka]

Re: Viewsonic VX2260WM LCD grey screen with lines

Hi Doorzon,
sorry for the late reply.

Voltages are the same on both LCD TCONs

Hmm... that suggests that the T-con may not be the issue. Nonetheless, I will explain some of the voltages below, because there are a few voltage readings that do seem off.

...

VR1 12.4
VR2 11.8
VR3 9.9
VR4 9.3
VR5 8.9
VR6 8.2
VR7 7.3
VR8 6.3
VR9 5.3
VR10 4.4
VR11 3.8
VR12 3.2
VR13 1.0
VR14 0.3

Okay, they are the LCD gamma reference voltages. I think they are more or less normal.

VDDG 21.0V
VDDA 21.9V
VEEG -7.0V
VDDD, VDDD_P 3.3V
VCOM_1 5.1V

From these, VEEG and VDDG appear normal. But VDDA on most monitor T-cons usually refers to the main boosted rail (which is always lower than VDDG), and is typically 10-16 Volts.

Could we see some pictures of the reverse (component) side of the T-con? That way, I should be able to confirm if VDDA on this monitor is indeed the same "VDDA" that I normally see on other LCD monitors.

Checked the flat-cable assembly of both monitors, all pins connect end to end.

Try cleaning the ribbon cable contacts too. Believe it or not, pencil eraser works great for that. Follow up on that with some IPA (Isopropyl Alcohol).

At the moment I cannot measure the voltages on the signal board while connected to the LCD. Will solder some wires in place later to test the 5V/3,3V/1.2V when connected.

Lack of any of these voltages probably would cause the whole monitor to shut down, so I doubt they are the problem.

Another suggestion I have is to change the caps on the main and stand-by 5V rails on the power supply (they are marked as "VCC-5V" and "VSB-5V" on the main connector between the PSU and logic/video board.)

[doorzon]

Re: Viewsonic VX2260WM LCD grey screen with lines

Hi Momaka,

attached the pictures of the TCON component side.
I don't have access to my oscilloscope yet, otherwise I could look for excessive ripple on the VCC and VUSB on the power supply board. Maybe I'll just replace the caps on the board since it's little effort and cost. Only the wait time to get these shipped to New Zealand ;-). I suppose you learn to be patient when living on an island.
The fuse on the TCON is ok.

Will update when I have some more info.

thanks,
Doorzon

[momaka]

Re: Viewsonic VX2260WM LCD grey screen with lines

Maybe I'll just replace the caps on the board since it's little effort and cost.

If you are talking about the ones on the power supply board - yes, that would be a good idea.

As for the T-con, can you check what resistance you get between test points VDDG and VDDA? Also, can you check VDDG resistance to ground and VDDA resistance to ground? Finally, can you see what resistance you get between the cathode of SMD diode D501 and test points VDDA and VDDG?

You can see SMD diode D501 in this picture of yours, right above the round black inductor coil with numbers "100" on top:
https://www.badcaps.net/forum/attach...2&d=1452146386
Diode D501 has "24" written on it. The cathode side is the left side (the one with the stripe on it.)

The fuse on the TCON is ok.

Yes.
If it wasn't, you will get a uniform white or gray screen.

[doorzon]

Re: Viewsonic VX2260WM LCD grey screen with lines

Hi,

Between VDDG and VDDA: 33k4
VGGD - GND: 29k5
VDDA - GND: 1k8

D501K - VDDA: 0 R
D501K - VDDG: 31k4

Values are practically the same in both directions with my cheap DMM. Compared to 1% metal film resistors, the DMM seems reasonably accurate.

Diode testing D501 (in circuit) gives values 165 and 850 with my DMM.
Normally I'd expect one direction to be open but there are likely other components interfering with the testing.
So I took out D501 and tested. one way 165 and other way open, as expected from a working diode. It' back in now on the TCON.

The new part will be here around Tuesday, so then I'll replace all caps on the power board.

Could it be that one or some of the flex PCBs is making bad contact with the LCD glass conductors?

Thanks,
Doorzon

[momaka]

Re: Viewsonic VX2260WM LCD grey screen with lines

Between VDDG and VDDA: 33k4
VGGD - GND: 29k5
VDDA - GND: 1k8

D501K - VDDA: 0 R
D501K - VDDG: 31k4

Excellent.
So VDDA is indeed the main boosted rail as I expected, since it does have continuity to cathode side of diode D501.

Now the question is why VDDA and VDDG have the same voltage? They shouldn't - at least I haven't see it like that on any other T-con. But on the other hand, you said both T-cons have the same voltages, so it could be that they are normal.

Also, I'm just curious about those voltage measurements in post #6 - did you take them before or after playing with potentiometer VR601?

The new part will be here around Tuesday, so then I'll replace all caps on the power board.

Okay, keep us posted.

Could it be that one or some of the flex PCBs is making bad contact with the LCD glass conductors?

That could be it, too. I just hope that it isn't, since that usually means monitor is (economically) unrepairable.

You could try moving and flexing those flat ribbon cables between the T-con and LCD TFT to see if the problem will go away or at least change. If it does, then probably that's the problem. Also try moving around the LVDS cable between logic board and T-con.

[doorzon]

Re: Viewsonic VX2260WM LCD grey screen with lines

Hi People,

sorry for the late reply. It's been holidays in NZ and the site was unavailable for a while.

The caps have been replaced on these monitors, but no such luck fixing them. It seems that in spite of all the effort, the issue is with the LCD screen itself, as 1Supertech indicated in one of the earlier posts.
After taking apart the LCD itself, I've come to the conclusion that repair is not possible, but the monitors are a very nice uniform light source without the LCD glass panel in it.
This will be the next project to make the monitors into a variable light source driven by a simple micro-controller for making photos of small objects.

Thanks everyone for the effort, guess this one was impossible to fix.

doorzon

[momaka]

Re: Viewsonic VX2260WM LCD grey screen with lines

Sorry to hear it couldn't be fixed. But I guess not everything is (economically) repairable indeed.

...but the monitors are a very nice uniform light source without the LCD glass panel in it.
This will be the next project to make the monitors into a variable light source driven by a simple micro-controller for making photos of small objects.

Yeah, I think other members here have done this as well (don't remember the thread name, though). Maybe show us yours in a new thread when you start/WIP/finish it, too.

[edinson]

Re: Viewsonic VX2260WM LCD grey screen with lines

greetings I have the same problem with this monitor could you solve yours