Acer AL2423W Recapped, backlight works but no display

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

dondrusco; is it the PCB under this shield you mean in the attached picture?
And where do I measure the voltage of the pins, under the PCB (where it connects to the panel?)
What happens if I get dust on the panel, can I just remove it with a lens cleaning tissue for my camera for example?

And what voltages do I expect on these pins?
Are they listed in the service manual?

[jetadm123]

Re: Acer AL2423W Recapped, backlight works but no display

Hello Per. I think what dondusco is referring to is the same board I described in my earlier post. As an example, I've included a photo of my Viewsonic. It's the board at the top (spanning the width of the monitor) with the plastic cover folded back. I think yours is located under a metal cover.

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

dondrusco; do you mean the small PCB that connects to the panel directly?

I'm currently trying to follow the troubleshooting guide in the service manual
The voltages for the Mosfets checks out as we already know

Next on the list is the Crystal next to the CPU, it should be 14.318Mhz
Now I don't think my Fluke 113 TRMS meter can read hertz, so I broke out my CHY 17 multimeter
It has two hertz modes, one called Lo and one called Hi (Trig)
Now in both modes I get values that are changing, and in the KHZ range, not MHZ (around 40KHZ)
Now the specs for the meter says this:
"Frequency Ranges: 10 Hz–2 kHz–15 MHz"
In a Chinese manual it mentions this;


Now I wonder if I'm just doing it wrong or have I actually found the culprit?

CHY 17 Manual (Chinese)

[dondrusco]

Re: Acer AL2423W Recapped, backlight works but no display

Hi, Per!

You are much deeper in knowledge of AL2423W than me with this experience!

I had similar problem with AOC monitor - no display. It had broken LVD connector - when I replaced it, picture appears.
I have one suggestion, dismount bezel from LCD panel electronics and check voltage on pins 28-30. There might be the problem.

dD

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

Ok, I've been poking allot at this thing today, not much success tho

I added a serial header to CN3, I posted about it's measured voltages here
When I used a RS232 > RS422/485 level shifter I got only a celcius sign (°) in hyperterminal when I started the monitor with the cable connected...
Adjusting the hyperterminal settings made the one character output change but nothing else than that
The level shifter I am using is made by Sparkfun; http://www.sparkfun.com/commerce/pro...roducts_id=449
Now my assumption is that I am supposed to connect it to GND (obviously) and then to the fourth leg which sends out 5v to VDC (so the middle two legs would be TX and RX)

This turns my level shifter into one mode, if I power it from 3.3v it goes into another mode, so I next connected GND to GND, and VCC to the pin right next to it
But now I got nothing at all, either way I connected the TX/RX cables...

At this stage I found an old post where pedro said he had a service manual for this logic board, so I asked him for it and he sent it to me, thank you very much pedro (It confirmed that my first test with GND on GND and VCC on 5v was correct, so TX and RX indeed are in the middle of the pins...)
This manual informed me that this header is supposed to be connected with a software called gProbe (Genesis Probe)
I found that after asking nicley on a Russian forum
However I get no communication at all in either mode with the serial cable using it

So next I started reading more on the JTAG header (J1)
I have a GQ-4X USB Universal Programmer with the ADP-056 adapter
I am now trying to figure out the pinout of the JTAG header on the board but it is difficult, because the markings on my programmers adapter and the service manual are different...

Here are the voltages I measured against ground with the monitor running:
1: 0
2: 0
3: 3.3v
4: 0
5: 3.3v
6: Infinity

Note that I have simply numbered them left > right in respect to this image taken here of the PCB: https://www.badcaps.net/forum/attach...1&d=1399820346

I think they map like this to my programmer, using a crop from the service manual of the relevant section:


1 > ?
2 > ?
3 > TDO
4 > TDI
5 > TCK
6 > TMS

So yeah, those two question marks would be nice if someone could help me with
On that Russian site was a firmware from this monitor posted, so what I'm going to do is save the firmware I have now as a backup and try flashing that to see what happens...

Finally I've attached some pics, both top and bottom this time...
Also I attached a part of the service manual, when I got the whole thing from pedro I was able to find this one via Google which has only the relevant things listed (part numbers and schematics)

[PlainBill]

Re: Acer AL2423W Recapped, backlight works but no display

Hmm, I don't have enough experience to judge, but all the voltage regulators are AC 1084 0553AL, but the one closest (U13) to the power board measures significantly lower than the other 2????

Now it is possible that is "normal" for this design.

Yes. These regulators are available in fixed and variable output versions.

The pins are numbered 1, 2, 3 across the bottom. 3 is the input, 2 the output, 1 the adjust. By using a pair of resistors from pin 2 to pin 1, and from pin 1 to ground it is possible to set whatever voltage you want. If you notice the voltages, pin 2 is 1.2 volts higher than pin 1.

PlainBill

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

retiredcaps; Yes, I made the same observation
I checked with two multimeters just to make sure, with my Fluke 113 TRMS meter in auto mode it went a little crazy, but I know it has problems auto sensing low voltages otherwise too (below 5v inside PC for example)
But both it and my CHY17 showed roughly the same value

I found this thread now, it shows some details of the logic boards controller chip
I suspected it was a Genesis and this seems to confirm it (have not removed the heatsink from mine yet tho)

But the PDF they link to is dead, however I managed to find it on Archive.org, so I attached it to this post...
It mentions the controller chip has a serial interface, and also an x86 CPU
So now I will try to connect to this and see what I get, but that will be a project for tomorrow, time is late in Sweden now



CN3 which I marked out with voltages is probably a RS422 serial interface
J1 on the right is probably JTAG

[retiredcaps]

Re: Acer AL2423W Recapped, backlight works but no display

I did some measurements now

Hmm, I don't have enough experience to judge, but all the voltage regulators are AC 1084 0553AL, but the one closest (U13) to the power board measures significantly lower than the other 2????

Now it is possible that is "normal" for this design.

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

Thanks for your nice comments guys
I did some measurements now, I started the monitor with the PSU and logic board laying the wrong way around (components facing up) with a blanket under for short circuit protection
I also connected the two PCB's ground planes together because I noticed that there was no continuity of the ground otherwise (Normally the metal box these two boards sit in would connect them together via itself so I felt it could be unsafe to start it without this connection...)

I added text to the image posted here on badcaps, it shows what voltages I measured on the Mosfets
There is a full resolution image of this picture without the text obscuring the view here: https://www.badcaps.net/forum/attach...1&d=1399820756
I'm unsure if this is the correct PDF for the "1084" Mosfet, but maybe:

[jetadm123]

Re: Acer AL2423W Recapped, backlight works but no display

Thanks for the photos! I have the same problem with a Viewsonic that I've been working on. And by the way, your English is very good! Sometimes, what happens is that while I'm typing a reply, someone may have already posted a reply before me, which may lead to some confusion because some of the replies may be out of sequence. I'm hoping I make sense!

[retiredcaps]

Re: Acer AL2423W Recapped, backlight works but no display

Ok, thank you, I think it was jetadm123 that was most confused by my wording tho

Your English will be better than my Swedish anyday.

Did you try testing the voltage regulators as PlainBill suggested? I believe they are the chips marked 1084.

What you are seeing with this monitor is similar to the issue I have with the Daytek (not resolved yet).

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

Ok, thank you, I think it was jetadm123 that was most confused by my wording tho

Just for kicks I used my old Konica KD400Z to try to make a movie, I was not expecting it to work and it didn't, turns out I have allot of dead pixels on my old trusty Konica aswell (Not that I didn't know already)
Note that these are taken in the exact same light enviroment as the pics from the SLR, at the same time also

[retiredcaps]

Re: Acer AL2423W Recapped, backlight works but no display

I am sorry about my English, I understand it gets confusing

There is nothing wrong with your English. I'm just trying to get a very precise understanding of the problem to eliminate certain things.

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

If you can please post a photo of the entire back of the monitor with all boards mounted and connected, it might make more sense. Thanks!

I am sorry about my English, I understand it gets confusing
I assembled the monitor, attached is a picture of how it looks

Also I took a picture of it with my SLR in manual mode, I tried to match the colors as best as I could, it is actually very close to how it looks in reality;
(Note that this image never changes, I've left it connected for a few minutes and it always looks like this...)

The problem is unusual. This power supply is actually a dual supply with a 5 volts standby supply and 12 and 19 volt main supplies. The fact that you have all output voltages, backlights, and a black screen indicates that many functions of the logic card are working, but it's not processing video, nor is it responding to the buttons.

Yes I agree, it is very hard to troubleshoot
Also don't forget the fact that I got EDID data through the DVI cable with GPU-Z as I showed in the first post...

What is even more puzzling is what appears to be a hammer in the background of one picture. I sincerely hope that was not used to fix any problems.

Hahaha, no, it was not used to fix things
The logic and power supply combo metal box when installed the wrong way (so I can measure with a DMM) has too short cables, so the rubber end of the hammer was used for strain relief for the cables

The pictures of the logic card are clear, but taken at a sharp angle that limits their usefulness. I would appreciate if you could provide one taken from directly overhead. There are a number of what appears to be voltage regulators that should be identified and tested.

Ok, I will deassemble the LCD again and take some better pictures, I will take pictures of both sides of the logic card

Thank you for your input guys!

[jetadm123]

Re: Acer AL2423W Recapped, backlight works but no display

Yes, PlaninBill is correct. Sorry, I missed the part where you initially said it was a white screen, then changed it to a black screen. My suggestion would only hold true for a white screen.

[PlainBill]

Re: Acer AL2423W Recapped, backlight works but no display

I believe jetadm123 was referring to the 'panel card'. This is part of the LCD panel. It has the connector the cable from the logic card plugs into. That does not appear to be the problem, usually when the fuse on it blows you get a 'white screen' problem.

The problem is unusual. This power supply is actually a dual supply with a 5 volts standby supply and 12 and 19 volt main supplies. The fact that you have all output voltages, backlights, and a black screen indicates that many functions of the logic card are working, but it's not processing video, nor is it responding to the buttons.

What is even more puzzling is what appears to be a hammer in the background of one picture. I sincerely hope that was not used to fix any problems.

The pictures of the logic card are clear, but taken at a sharp angle that limits their usefulness. I would appreciate if you could provide one taken from directly overhead. There are a number of what appears to be voltage regulators that should be identified and tested.

PlainBill

[jetadm123]

Re: Acer AL2423W Recapped, backlight works but no display

If you can please post a photo of the entire back of the monitor with all boards mounted and connected, it might make more sense. Thanks!

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

No, the panel stays on, the backlight is lit
But it is a black screen, i.e. the LCD is not letting through the backlight
I.e. it is the most black the LCD can produce if you understand?
(I can post a pic if you want but right now the LCD is in many pieces )

[retiredcaps]

Re: Acer AL2423W Recapped, backlight works but no display

retiredcaps; oh sorry misread your first post
No, it is a black screen, i.e. it is not letting through any light (except what bleeds through the panel)

jetadm123: I believe you are speaking about the backlight PCB?
But since my backlight does come on properly can't we rule that out?

Maybe a picture of the problem is warranted here since the two answers are seem to be conflicting? Even a video posted on youtube would help.

Are you getting 2 seconds to black?

[Per Hansson]

Re: Acer AL2423W Recapped, backlight works but no display

retiredcaps; oh sorry misread your first post
No, it is a black screen, i.e. it is not letting through any light (except what bleeds through the panel)

jetadm123: I believe you are speaking about the backlight PCB?
But since my backlight does come on properly can't we rule that out?