Monitor won't turn on (solved)

[AndreyS]

I have monitor Belinea 11 19 28, it has same board as ASUS PM17TE (board: 200-100-DA985D).
The problem is that if monitor is connected with vga to the laptop or PC it won't turn on, instead it is repeatedly turn on (for 2-3 sec, green LED lit) and turn off (for 1-2 sec, no LED lit).
If I disconnect VGA cable, it will cycle through some time (2-20 min) and then goes into stand-by mode (orange LED lit). After monitor is in stand-by mode I connect VGA cable and it works.

What more interesting is that if connected with DVI-D cable it works perfectly: at first time turns on.

I replaced almost all cap (including 3 bulged and 10-15 suspects), it didn't resolve the issue.
Monitor's power supply supplies steady 4.85-5.0 Volt (varies when on-off cycling, steady when on).

Boards do not seem damaged.

A guy BassHole in this forum describes same problem.

Did anybody encounter similar issue? Any ideas what to check/replace next in order to fix the monitor?

[AndreyS]

One more thing.
I have two different VGA cables: one has almost all unused pins grounded, another one has not.

With cable one it immediately turns on and stay on, but the screen quickly changes into white. I have to unplug and plug in power cable few times until the screen displays destop (not white backlight).

Both cables are ok, and work perfectly with other monitors.

Monitor is well grounded including pcb and vga ground

[AndreyS]

When LVDS cable is disconnected from the board it goes into stand-by mode after plugging in power cord.

[Rasz]

belinea = caps

[AndreyS]

I replaced almost all caps. Power supply is in working condition 100%.
5V is OK, Brightness level control works, light on/off pin works.
12 V is 14.5 V actually, but is only used for speakers.

[Rasz]

does the laptop/computer see that switch on/off? as in second monitor showing up and being removed constantly?
maybe I2C eprom died?

[shakalnokturn]

I do not know of your model but I've had similar and other hard to explain problems on monitors due to corrupt firmwares themselves often due to worn PSUs.
In seeking firmware dumps the Russian fora are the best place to look.

[Rasz]

replacement pcb is ~$5 http://allegro.pl/main-200-100-da985d-nr-3802-i6834294863.html
but 100% working 19 inch monitor itself is worth less

just keep using DVI if that works

edit: it looks like two i2c eproms are in the middle of pcb U4 U5, you could try swapping them with each other (if those are really i2c eproms)

[AndreyS]

I've found a firmware for my monitor (exect model). Yes, those are real i2c eproms.
Also I decided just in case to solder my external 5 V and 12 V power supplies omitting built-in one. I desoldered transformer. Also I discovered a blob dripped (most likely) from the transformer. See attachments, the blob is located under the transformer, indicating that gravity pulled down that substance from the transformer.
After soldering 12 V and 5 V power supplies, the monitor worked perfectly.
It is still a mistery on why it did work with dvi-d connected to a PC and not with VGA.
If anybody can explain this, I'd be eternally thankful.

As for the monitor's PSU. Is the transormer a culprit of this? My explanation on why 12 V line was 14 V is that 5 V coil's isolative coating melted and it created a short, effectively reducing number of windings. That led to drop in voltage on 5 V line. Since optocoupler is connected to 5 V isolated line, it fedback into IC, which stabilized 5 V line, but also increase 12 V line. Is this explanation plausible?

As for repair, firstly I want to get what a real culprit is. If it is the transformer, I'll just remove that part of a PCB and insert PCB from 12 V PSU and buckconverter to 5 V. Monitor takes 1.3 A @ 12V and 1.3 A @ 5V. Therefore 3A@12V is sufficient.

[AndreyS]

The point is to use it with my laptop. I cannot use DVI

[GreyWoolfe]

The point is to use it with my laptop. I cannot use DVI

VGA to DVI Adapters are available and cheap.  I use them here.

[AndreyS]

the monitor has DVI-D, that means the converter is needed (not just wiring) in order to convert analogue VGA to DVI-D

[Rasz]

It is still a mistery on why it did work with dvi-d connected to a PC and not with VGA.

VGA requires 3 very fast ADCs and recovering/locking clock, DVI is pure deserialization, much less power hungry
starting to work after some warm-up time = caps, or maybe intermittent solder joints

[AndreyS]

I've replaced all electrolytic caps and replaced transformer for similar.
Now it PSU won't start. Some short hissing noises are hearable out of transformer, and voltage on controlling IC is rising to 5V and then suddenly drops to 0V every 0.8 sec.
The voltage on IC is supposed to be 12V at start and 7V at continious working

[AndreyS]

I fixed it by removing 10 Ohm limiting resistor for IC at AUX coil.
Now it works as supposed: 5.01V, 14.5V and 8.75V on aux (IC)

[AndreyS]

I suspect AUX coil inductance of replacing transformer is slightly lesser than on original.

[yesyesufkurs]

Hi, I actually have a question regarding the 200-100-DA985D controller board. The 10 pin power connector on the board that connects to the PSU, could it be possible to power the screen using a Molex cable from my PC PSU? Molex has the following pinout +5V/Gnd/Gnd/+12V, and I only need the LCD panel to turn on, I don't need the speakers or backlight. Could it be possible to wire the +5V cable from the Molex cable to the +5V pin on the controller board and wiring the ground cable to the ground pin next to the +5V pin?

Thanks!

[AndreyS]

Yes, it will work.
I tested my monitor by connecting it to two power adapters 5v and 12v.
But I would make sure that the current from your molex connector flows only to your lcd circuitry and not back to monitor's power supply. Just break the circuit (desolder some jumpers/diodes). Just in case

[tooki]

It is still a mistery on why it did work with dvi-d connected to a PC and not with VGA.

VGA requires 3 very fast ADCs and recovering/locking clock, DVI is pure deserialization, much less power hungry

Yes, but the chipsets in cheap LCDs do that just fine, and active VGA to DVI/HDMI converters don’t cost very much at all. I used one a few years ago when setting up the conference room projector at work, so that we could have a single HDMI “umbilical cord” snaked through the walls and ceiling, with HDMI, DVI, DisplayPort, and VGA inputs right in the conference table. (The new projector’s WUXGA (1920x1200) resolution got too blurry with the long VGA cable that worked fine at 1024x768, and the VGA->HDMI converter cost a lot less than a high quality VGA cable that could handle WUXGA at the length needed. We had to run HDMI anyway, so using the converter was a no-brainer.)