ViewSonic VX2255WMB White Screen Problem

[codeMonkey]

I've already recapped this monitor, but I then had a white screen. I found that fuse F1 on the back of the LCD was blown so I replaced it with a LittleFuse 1.5A 63V SMD fuse. Is this the correct amperage and voltage for this fuse? Once I replaced it the monitor worked fine. However, when an additional monitor is added and all the screens go black for a moment as the new configuration is set the fuse blows again and I once more am left with a white screen.

My guess is that there is a spike that occurs (because of a bad inverter or perhaps transformer). I've tried to hit all specifics in the attached pictures.
When it's plugged in I can hear a very audible buzzing noise coming from the transformer if that's what it is (circled in green). The other monitor that I have (same model) doesn't make this noise. I am I on the right track with this one or might it be something else? If I'm on the right track, can someone tell me what the specs are so I can find a replacement? Also if there's an easy way to test this please let me know.

I've included other pictures for reference and also to eliminate anything I've already tested. The transistors Q205 & Q208 tested with diode test and a resistance test and both passed.

If anyone can help me out with this one I'd greatly appreciate it.

[retiredcaps]

Originally Posted by codeMonkey

I found that fuse F1 on the back of the LCD was blown so I replaced it with a LittleFuse 1.5A 63V SMD fuse. Is this the correct amperage and voltage for this fuse?

If the original was "K", then 1.5A is correct according to

http://forums.xbox-scene.com/index.php?showtopic=658938

I don't know about the voltage rating.

When it's plugged in I can hear a very audible buzzing noise coming from the transformer if that's what it is (circled in green). The other monitor that I have (same model) doesn't make this noise. I am I on the right track with this one or might it be something else? If I'm on the right track, can someone tell me what the specs are so I can find a replacement? Also if there's an easy way to test this please let me know.

This website has two 2874 transformers, but they don't match yours exactly.

http://lcdparts.net/T.aspx

You can contact them for more details.

One has 610 ohms and the other has 650 ohms for its secondary resistance.

You can test your transformer with a ring tester or if you don't have one, try this method "Testing for Faulty Inverter"

http://www.youtube.com/watch?v=eNuGWBPRGKA

[codeMonkey]

Thanks a ton Retiredcaps. I'll test the inverter as soon as I get home from work. I'll post results and pics (if applicable) afterwards.

[retiredcaps]

Originally Posted by codeMonkey

However, when an additional monitor is added and all the screens go black for a moment as the new configuration is set the fuse blows again and I once more am left with a white screen.

So just to clarify.

1) If this monitor is used in a standalone configuration, then it works fine? If yes, what port are you using? VGA or DVI?

2) If this monitor is used in a dual configuration, then it blows the fuse? If yes, what is the other monitor's configuration?

3) What type of graphic card is being used to drive these monitors? Have you checked the graphics card for blown caps or bad transistors?

[codeMonkey]

Originally Posted by retiredcaps

So just to clarify.

1) If this monitor is used in a standalone configuration, then it works fine? If yes, what port are you using? VGA or DVI?

2) If this monitor is used in a dual configuration, then it blows the fuse? If yes, what is the other monitor's configuration?

3) What type of graphic card is being used to drive these monitors? Have you checked the graphics card for blown caps or bad transistors?

1) I haven't tested the monitor in a standalone configuration. A bit daft on my part perhaps. Using DVI.

2) This monitor was used in a triple monitor setup. When I'd remove one of the other monitors for testing and all the monitors go black to adjust resolution properties this monitor will come up white screen (fuse F1 blown). This monitor and the other wing monitor have a resolution of 1650 x 1050 and the center monitor has a resolution of 1920 x 1080.

3) ATI Radeon 4870 2GB. I haven't checked it for blown caps so I'll do that as well tonight, but it's currently driving the center monitor with no issues. The other monitor is driven by an external USB DVI video card adapter. If I'm not mistaken I've tested the other dvi output from the video card with another monitor. In any case, once I've checked for bad caps on the video card I'll test it with one of my other old monitors.

Will post follow up.

[seanc]

You've checked the PSU for bad caps yes?
I had one of these with bad caps - as have many other people.

[codeMonkey]

Ok, Caps on the video card and on the monitor boards tested good. The transform that I thought might be the problem tested good as well I think. (It would be replaceable by PN:2874014700 on lcdparts.net.) The other inverter also makes makes some odd sounds but I'm less inclined to think that's my problem now, but it could be. I did note what looks like a bit of corrosion in the attached pics. Any ideas on how to test this inverter?
Outside of that I think I've tested pretty much every resistor, cap and diode on the monitor. The only other thing of interest that I found is that the diode at D106 reads .008 in both directions. Since none of the other diodes be have in this manner might this be the culprit? I may be grasping at straws here, but I realized that I'm just about at a point where I'll have to throw in the towel.

Thanks for the input everyone.

[codeMonkey]

I've tested the video card itself with a dual setup (hdmi/dvi) and it works great. I think thus far the white screen problem has been the toughest thing I've tackled.

[PCBONEZ]

If you tested the diode out of circuit and got that then it's bad.
In circuit there might be a parallel path which makes the reading useless.
.

[codeMonkey]

Good point. I'll have another go at it tomorrow. Thanks.

[codeMonkey]

I don't know if bammbammfran is part of this forum but he seems to be a pretty good tech based on reputation. I'm going to put everything back together and focus testing on the board mounted on the back of the LCD. I've been assuming that the issue is happening before that board but that may not be the case. I'll post an update tonight after testing the board. If anyone knows of a component besides the fuse that usually goes bad on the LCD board let me know. Here's what bammbamm had to say:

f1 fuse on lcd screen board
If you mean the long narrow board that is attached to the back of the screen ? (first- that board is not removable) Second: if that is the fuse that is popping, then that board is more than likely the problem. Probably has a dead short in it somewhere, Ohm it out and you might be able to verify this.
You can check to see if too much voltage is getting to that fuse, but I have my doubts. Most screens are around 5 volts dc. I have seen a couple that run higher, but not often.
If the problem was in the dac board, it probably would not stay lit at all, if it stays on white screen then it is probably ok

- bammbammfran

[PCBONEZ]

I dunno what the 'long narrow board" is. - You didn't show one.

You 'corrosion' is just soldering flux.

When you have white screen it means the backlight [and so the inverter] is working fine but the video is not going through.
That would make the DAC or the GPU or the power board the probable faulty sections.

[Wrog]

Originally Posted by PCBONEZ

I dunno what the 'long narrow board" is. - You didn't show one.

I'm guessing the long narrow board is the one bonded to the LCD panel (photo #4 in the first post).

[PCBONEZ]

Okay. - Didn't scroll up that far.

[codeMonkey]

I've checked EVERY single resistor on this monitor. I've come across 9 resistors that were shorted. However, I don't know the proper resistance measurements so if some one has the same monitor and can check I'd greatly appreciate it. There is I realize, a possibility that some of the resistors have to low a resistance for me to measure, but again I need some sort of confirmation. (I'm using a Mastech MS8268 DMM.) Picture 1 is of the video control card with the shorted resistors marked and picture 2 is of the LCD board that's attached to the screen. Where possible, I've marked what I think the resistances might be based on other resistors nearby. This is only done if there is a line of several resistors with the same value that lead me to believe that one shorted in the same group would have the same value.
Shorted resistors in question:

Pic 1:
R78 96.2KΩ (maybe, should be ?)
R22 ???
R39 ???

Pic 2:
R100 ???
R101 ???
R102 ???
R15 ???
R95 33Ω (maybe, should be ?)
R97 33Ω (maybe, should be ?)

Some of these are going to be a pain to solder, but if it works... woot!

[codeMonkey]

Alright,
I guess it's time to through in the towel here. This is well beyond the scope of my knowledge and capabilities and there doesn't seem to be much to go on in regards to white screens.

I'm going to sell this one for $25 plus shipping to who ever wants this for the power board and back lights and any other useful parts. Otherwise I'll just toss it.

Thanks to everyone here for the help and advise.