Benq G2400W 2 second to black problem

[hechacker1]

Recently my Benq g2400w started exhibiting the "2 second to black" symptom. When I turn it on, the display will work fine for about 2 seconds before turning off to black.

I can switch inputs to VGA, DVI, or HDMI, but the symptom persists.

I suspected perhaps it was bad caps, but they all look fine from an external view. I also used my cheap multimeter to see if they charged up, and they do. I also tested all the diodes I could find, and they read approximately right values 0.6-0.8 volts
I looked at all the solder joints, and even reflowed a few that looked potentially weak, but it hasn't helped.

I checked the fuse, it reads .3 ohms.

I did see this thread,

https://www.badcaps.net/forum/showthread.php?t=10419

but it wasn't specific to my monitor's power supply. Perhaps you could help point out some components I should look at.

Here's the full quality jpegs, because this site resized and shrank them:

http://ordorica.org/system/misc/benq...ly%20front.JPG

http://ordorica.org/system/misc/benq...ply%20back.JPG

Any help would be appreciated. I do like this monitor and it would be a shame to throw it away because of this. Unfortunately, all I have is a basic soldering iron and multi-meter.

[retiredcaps]

Re: Benq G2400W 2 second to black problem

2 seconds to black can be

a) bad caps
b) bad inverter transformer
c) bad ccfl
d) bad ccfl wiring

Since you already found the guide, test for a bad inverter transformer.

Refer to

http://www.lcdparts.net/TransformerD...ProductID=2731

for the secondary pins. Measure the resistance between S1-S2 and S3-S4 for both transformers.

All 4 readings should be within 3% of each other.

[hechacker1]

Re: Benq G2400W 2 second to black problem

1st Transformer:

S1-S2: 1.03K
P1-P2: 0.3
P3-P4: 0.3
S3-S4: 1.03K

2nd Transformer:

S1-S2: 1.04K
P1-P2: 0.3
P3-P4: 0.3
S3-S4: 1.02K

[retiredcaps]

Re: Benq G2400W 2 second to black problem

1) Your transformer readings are good.

2) This is low probability, but on the back of the pcb are 4 mosfets: Q805, Q806, Q807, and Q808. In the guide, there is a procedure on how to identify and test those mosfets for shorts. Post your findings.

3) If the mosfets are fine, then the next step is to check your ccfls.

4) PS. Great photos with good focus and composition. I don't think we have seen one on a tire yet though.

[hechacker1]

Re: Benq G2400W 2 second to black problem

I checked out the mosfets you asked for. It's hard knowing whats the source, drain, and gate, but with the continuity tester I found the drain is all connected on the left side. So I guess it looks something like this although the source and gate may be in different pin locations.

http://www.datasheetdir.com/MTN4410Q8+N-Channel-MOSFETs

Anyways, none of the combinations of results in a reading lower than 200 ohms for

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms.

I was able to also test the internal diodes of the mosfets, and they read right (0.5-0.6 volts).

The photo was on top of a tire swing. Taken with my old but good Canon S400.

So the next step is to check the CCFLs? I don't have spares, so does that mean I won't be able to test? I actually have a computer case CCFL that had its connector stripped. Something like this:

http://www.amazon.com/WHITE-CATHODE-.../dp/B000JQ17WU

Or perhaps I can only connect one at a time? (From the 4 connectors, I guess I have 2 CCFLs in the monitor).

EDIT: I should read better, I see I can test them one at a time.

[hechacker1]

Re: Benq G2400W 2 second to black problem

Ok, I tried plugging in the CCFLs one at a time, but the 2 seconds to black problem persists.

Any thoughts on what I can try next?

[jayoung]

Re: Benq G2400W 2 second to black problem

The 4 connectors are for 4 ccfl's, typically 2 ccfl's along the top of the monitor and 2 ccfl's along the bottom of the monitor. Testing 1 ccfl at a time will result in 2 seconds to black because of the sensing circuit. It might however show if a ccfl wasn't lighting at all bacause of something like a broken wire or broken ccfl. Did all 4 actually light up initially and then shut off? Or did one or more just stay black?

[retiredcaps]

Re: Benq G2400W 2 second to black problem

Testing 1 ccfl at a time will result in 2 seconds to black because of the sensing circuit.

It might however show if a ccfl wasn't lighting at all bacause of something like a broken wire or broken ccfl.

[retiredcaps]

Re: Benq G2400W 2 second to black problem

Any thoughts on what I can try next?

Take it apart and look for

http://s807.photobucket.com/albums/y...klight%20lamp/

[hechacker1]

Re: Benq G2400W 2 second to black problem

Argh,

This monitor is hard to disassemble. The CCFLs are buried in layers of plastic and metal.

I just removed the LCD layer, and I see another logic board on it.

Well, I'm off to take it apart so I can see the CCFls.

[hechacker1]

Re: Benq G2400W 2 second to black problem

Ok, so there are four CCFLs, in pairs. 1 on top, 1 on the bottom.

They all light up fine for about 2 seconds. They are not pinkish. All of them show burning on the ends, like this:

http://s807.photobucket.com/albums/y...t=DSCF2058.jpg

So is that the issue?

[retiredcaps]

Re: Benq G2400W 2 second to black problem

All of them show burning on the ends,

Yes, that is the issue causing 2 seconds to black.

As ccfls age, they draw more current and that causes the pwm chip (IC802 on the backside) to shut them down (for protection). The pwm chip operates as "all or nothing". Either all the ccfls work or none at all.

You can buy bare ccfls and try replacing them as per

http://www.ccflwarehouse.com/lasotu.html

or buy them pre-harnessed/assembled from the same place above.

Cclfwarehouse.com has good feedback from members here. You can call them, get a live person, and they can help you find the correct replacements as well as a price.

Other alternatives are ccfldirect.com and ebay.com.

[retiredcaps]

Re: Benq G2400W 2 second to black problem

Supposedly, ccfls have a 30,000 to 50,000 hour lifespan and that varies a LOT due to different manufacturing quality.

Since it looks like this monitor was made in 2007 Nov 12 or Dec 11, it has seen 4 years of use.

If you have used this monitor 24/7 at the default settings (something like 80/100 brightness and 90/100 contrast) and don't use sleep mode, then

365 days x 24 hours = 8,760 hours/year.

4 years x 8,760 = 35,040 hours

[hechacker1]

Re: Benq G2400W 2 second to black problem

Does it have to be exactly the same size in length and width?

My monitor has 525 mm sized CCFLs, and only a few of the diameters listed on that site go up to that size. Or I'd have to get custom sized ones, which are too expensive in my opinion.

Do all the sizes use the same power? Because that's what would matter for my case.

Actually, I use sleep mode on it, but it probably got close to 12 hours of use daily though.

[hechacker1]

Re: Benq G2400W 2 second to black problem

Oh, and thank you for all your help.

[hechacker1]

Re: Benq G2400W 2 second to black problem

So my CCFLs are 525mm long, with a diameter of 2mm. At the ccfl warehouse, only the 2.4mm ones go up to that length. Would those be ok?

[alexanna]

Re: Benq G2400W 2 second to black problem

Ok, so there are four CCFLs, in pairs. 1 on top, 1 on the bottom.

They all light up fine for about 2 seconds. They are not pinkish. All of them show burning on the ends, like this:

http://s807.photobucket.com/albums/y...t=DSCF2058.jpg

So is that the issue?

If the CCFLS look like that the ones shown in the picture I am not convinced that they need replacing just yet.
Lube the silicone end caps and pull them away from the bulbs being careful not to tear them, inspect the wiring closely. Look for any change of color on the wiring where it is soldered to the CCFL, you might even give the wire a firm tug to see if it comes loose from the CCFL.If the wiring comes loose you will need to strip the insulation back enough to find good wiring.

[hechacker1]

Re: Benq G2400W 2 second to black problem

If the CCFLS look like that the ones shown in the picture I am not convinced that they need replacing just yet.
Lube the silicone end caps and pull them away from the bulbs being careful not to tear them, inspect the wiring closely. Look for any change of color on the wiring where it is soldered to the CCFL, you might even give the wire a firm tug to see if it comes loose from the CCFL.If the wiring comes loose you will need to strip the insulation back enough to find good wiring.

Actually, I can't really get a good look at the connection because it's all shrink wrapped. I'd have to cut it, and probably cut into the wire as well in the process.

I can if you think it'll help.

If we assume the CCFLs are ok, what could I do next to figure out the problem?

[alexanna]

Re: Benq G2400W 2 second to black problem

Have you removed the silicone end caps and given the return wires a good tug?
If the wiring is bad it will come loose from the CCFL

[hechacker1]

Re: Benq G2400W 2 second to black problem

It's secure. The shrink wrap is also holding it in place. No amount of tugging is going to detach the wire.