Dell U2312HMt garbled display

[dethica]

The screen works normally for about 5 minutes and then screen goes crazy: stripes, patterns etc.

The monitor is a relatively new model, I couldn't find any service manuals or schematics on this, and nobody seems to have similar problems with this model (yet!). Warranty is not an option, so I have to find a way to repair this myself.

Examining the logic and power boards, I could not find any bulging caps or bad solder joints on the caps.

I have repaired 2 other LCDs by replacing bad caps, but I don't know which ones to replace here, because they all look normal.

The larger caps on the logic board are 16V 100uF 105C and the small ones are 10V 100uF 105C.

any help would be appreciated.

[Lumberjack777]

Re: Dell U2312HMt garbled display

Can you post a picture of the garbled screen? There's a lot of trained eyes on this forum and the actual picture you see is important. This might also be a T-Con board problem.
You could start by checking the voltage regulators on the main board. I circled them in red. Retiredcaps has an excellent guide on this. https://www.badcaps.net/forum/showthread.php?t=22231

[dethica]

Re: Dell U2312HMt garbled display

It was something similar to this:
http://www.youtube.com/watch?v=Oh-7-6Yb0Oc

There was like a vertical interlaced effect everywhere, image was cut into pieces and was jumping up and down, like in that video.
I will assemble the monitor in the morning to take a picture and check out the voltage regulator readings.

regulators:
UTC
LD1117AG
12A01PAT2
http://html.alldatasheet.com/html-pd.../2/LD1117.html - supposed to be the 1.2V 1A variant.

N521
G1084-33
http://html.alldatasheet.com/html-pd...4-33T43UF.html - 3.3V 5A

this last one (the smallest regulator) I can't find:
D || 2GF <-- cant figure out what the first, second/third characters are
17-33

[budm]

Re: Dell U2312HMt garbled display

Try heating the caps on the logic board to see if the problem will go away, if it does then try heating small section at a time.

[lexwalker]

Re: Dell U2312HMt garbled display

It was something similar to this:
http://www.youtube.com/watch?v=Oh-7-6Yb0Oc

There was like a vertical interlaced effect everywhere, image was cut into pieces and was jumping up and down, like in that video.

Would be better if you could show us the actual picture rather than a similar one. For all that, could as well be a dirty LVDS connection. Have you tried cleaning those FPC connectors?

[selldoor]

Re: Dell U2312HMt garbled display

this last one (the smallest regulator) I can't find:
D || 2GF <-- cant figure out what the first, second/third characters are
17-33

It is likely to be a 1117-33 so fixed 3.3v

[dethica]

Re: Dell U2312HMt garbled display

I recorded a short video:
https://www.youtube.com/watch?v=yCXnIvf5IRM

I have also attached a photo:

[Lumberjack777]

Re: Dell U2312HMt garbled display

That video helps a lot! You need to do what budm said and heat the capacitors on the main board and see if the picture gets better. Post #4. If you are lucky its one of those caps on the main board. Next would be the voltage regulators. Selldoor figured out the 3rd one. Excellent work Selldoor.
Here's a video for everybody on fixing a main board with a bad voltage regulator. Norcal is an excellent technician and teacher. https://www.youtube.com/watch?v=cNFzBJELFoU

If you are lucky it will be a cap, or a regulator on the main board. Otherwise you are looking at T-Con or even worse.....bad LCD panel. Good luck!

[dethica]

Re: Dell U2312HMt garbled display

i tested the regulators:

N521
-- 0V
- 3.3V
-- 5.16V

UTC
-- 0V
- 1.2V
-- 3.3V

the supposed 1177-33
- 0V
- 0V
- 0V

Am I doing something wrong with the 3rd one? I couldn't get any readings from it at all.
I measured the regulators several times.
Also, the image stabilized after a while, then occasionally became garbled again and then stabilized again.
How much heat are we talking about with the caps?
the room temperature was ~25C when I was testing, this is what it looked like:

[selldoor]

Re: Dell U2312HMt garbled display

As it is working as well as it is I find it hard to believe they will be bad
but can you test the two fuses below (in your Picture) the 1117-33 regulator.

Test resistance with power off and with power on voltage on both ends


Heating caps - use a hair drier - not too hot though.

[Lumberjack777]

Re: Dell U2312HMt garbled display

the supposed 1177-33
- 0V
- 0V
- 0V

Am I doing something wrong with the 3rd one? I couldn't get any readings from it at all.
I measured the regulators several times.
Also, the image stabilized after a while, then occasionally became garbled again and then stabilized again.
How much heat are we talking about with the caps?
the room temperature was ~25C when I was testing, this is what it looked like:

The 0,0,0 volts to the 3rd regulator is very good news. And here I thought you might have a bad lcd panel *whew*!!
If you are saying the image stabilized after you heated that area; then the most likely culprit is a bad capacitor in that area around the regulator.
You should definitely test those 2 fuses F303 and F302 underneath it like Selldoor said. But it's probably at least one of those 6 capacitors around it.
I'm not an expert on reading circuitry from the top. Maybe you can isolate it, by heating them 2 at a time (together) like budm mentioned.

[budm]

Re: Dell U2312HMt garbled display

That one may be for the USB HUB controller chip, try hooking up the USB port to the PC.

[dethica]

Re: Dell U2312HMt garbled display

The 0,0,0 volts to the 3rd regulator is very good news. And here I thought you might have a bad lcd panel *whew*!!
If you are saying the image stabilized after you heated that area; then the most likely culprit is a bad capacitor in that area around the regulator.
You should definitely test those 2 fuses F303 and F302 underneath it like Selldoor said. But it's probably at least one of those 6 capacitors around it.
I'm not an expert on reading circuitry from the top. Maybe you can isolate it, by heating them 2 at a time (together) like budm mentioned.

I didn't try heating the caps yet, it was just very warm in the room.
I am still a noob with the multimeter - how do I go about testing the fuses?

I will try to hook the USB up to a PC and plug something in there to see if the 3rd regulator gives any readings.

[selldoor]

Re: Dell U2312HMt garbled display

Fuses test.

First no power to boards - set meter on ohms 200 - put one probe on each side of fuse.
take care not to touch any part of the board with your hands- could still hold a charge.

Then power it up and set meter on 200vDC put black probe on a ground screw and with the red + probe test each end of each fuse.

If read less then 20v then change meter setting to 20vdc for more accuracy.

[dethica]

Re: Dell U2312HMt garbled display

The fuses are ok, no resistance (monitor off) and 5.15v when USB device was plugged in (monitor on), so they're only there for the USB.

The 1117-33 regulator is okay too, it only works when USB was plugged in, the readings were:
- 0V
- 3.3V
- 5.15V

So I guess the only thing left to do is to check the caps by heating them, but that only works when the display is garbled, right? When the image stabilizes, I cannot test it?

[selldoor]

Re: Dell U2312HMt garbled display

Yes you can only try the hairdryer when it is in the fault stage.
An alternative might be to use a freeze spray /air duster to cool them when it is working ok but hairdryer is safest.

[Davi.p]

Re: Dell U2312HMt garbled display

U can use a soldering iron on each cap to warmup..
you don't have told nothing about cleaning/reseating of the lvds cable..
if is not that i think you have to concentrate forces on the t-con board and with the soldering iron you have to leave the monitor to cold up, then start some cycles of powering on and off where each time you warm a different IC and watch if the garble appear sooner than the normal..

[Lumberjack777]

Re: Dell U2312HMt garbled display

The 1117-33 regulator is okay too, it only works when USB was plugged in, the readings were:
- 0V
- 3.3V
- 5.15V

So I guess the only thing left to do is to check the caps by heating them, but that only works when the display is garbled, right? When the image stabilizes, I cannot test it?

Good catch by budm! Looks like that regulator is good afterall.
Yes you can heat the main board with a hair dryer when the picture is garbled to see if it gets better. What happens is that after an electrolytic cap heats up the ESR gets lower and it functions properly.

This may be more serious like T-con or LCD panel.

Lets just hope the hair dryer test makes it work. Then your problem would be a bad capacitor.

[budm]

Re: Dell U2312HMt garbled display

I would concentrate on those two set of caps I redlined. Group1 are for the input and output of the two regulators, Group 2 are for the voltage feeding the T-CON board.
This problem remind me of the HannsG 281 monitor with problem caps for the two regulator on the main board.

[dethica]

Re: Dell U2312HMt garbled display

I tried heating the caps just a bit by touching them with the tip of a soldering iron. They got warm, but didn't seem to stop the glitching. After that, I had no luck getting the screen to glitch for a whole day or so. I put the protective metal case back on and it started glitching again after 10 minutes.

I also noticed that "cap group 1" on budm's picture got slightly warm (when monitor was turned on), while all the other caps seemed cool to the touch.