Dell SE198WFPf - Backlights go off after 2 seconds

[WoR496]

Have a Dell SE198WFP 19" LCD Monitor. When turned on the back lights are on for about 2 seconds then they go off. There is still an image just no back lights. I've looked carefully over the power supply board (inverter board and ps board are integrated on this monitor), and i see absolutely no sign of bad caps, they all look great, no bulge at all or leakage. Could one still be bad without visible signs? I see many many posts elsewhere about people having the same problem with this monitor, but nobody ever posts if they find a solution.

Oh and the monitor is not going into standby mode, the power light stays blue and like i said the image is still there, just no back lights.

If anyone could clue me in i'd greatly appreciate it I can't even find any service info for the ps board that is in it.

[retiredcaps]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

If anyone could clue me in i'd greatly appreciate it

Start with post #13 and #14 and note the image posting guidelines.

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

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Well it would appear that the video board is doing its job, at least with the BLON. It works. It appears to be pin 4. When its off, no voltage, hit the power button, and no voltage until the backligh lights up, then it jumps to 3.33v and stays there but the bulbs don't stay lit up.

Here is the voltage readings i got on the other pins.

1 - 0.03
2 - 0.0
3 - 2.92
4 - 3.33 BLON
5 - 0.01
6 - 0.01
7 - 4.95

[romansroad]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

I may have missed seeing this, but have you tested the ccfl's? I know it's a pain to crack open the screen, but if one of the four is poorly soldered or dead, it will signal the logic board to shut off all the backlights.

You can substitute a resistor for a backlight (search under this to see that thread). I would then sequentially go through the turn on steps with the resistor placed at each separate HV point. If the other ccfls stay on, then the one you faked out the PS board with the resistor is the bad ccfl.

Unfortunately, you then get to crack the case. Ugh.

BTW, I have a black cat, and that hair gets EVERYWHERE inside the screen when I do this......I need a clean room!

[romansroad]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Oh yeah, the caps can still be bad even with no bulging, but I'd go with the ccfl's as well. THe caps are cheap and easy, but I'm suspicious you have ccfl trouble. Any idea what the age of the unit is? I just fixed an HP W2007 that actually has a backlight counter to age the lights....pretty cool!

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Guess i should test them lol just one question, there is no voltage on any of the pins that changes after the bulbs come on. The only thing that ever changes is the BLON goes from 0 to 3.33v and the bulbs light up, but just for a second or so, then they shut off. but the BLON voltage stays up so wouldn't this indicate that in fact the logic board could not be the cultprit because it is still providing a BLON signal to the power/inverter board. which the leads on my dvom were smaller, i'd just compare resistance between the bulbs and see if i have an oddball, or can you do that with a ccfl? i guess if there is just gas in there then theres not much of a conductor to measure resistance on lol

Thanks, i will look into the ccfl testing and try that out. I'm pretty sure this unit was made in 2007-8.

[George Ortiz]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

WoR496,
could you explain how you pulled your monitor apart. I have the same model, except mine is working but has a vertical and a horizontal line thru the display. I have pulled the stand off (4 screws) and then removed the front bezel, but am having problem pulling the 4 connectors to ccfls and then the white mylar cable.

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

well i was messing with it more and using the limited testing tools i have ( a dvom lol) i'm pretty sure all caps are good. I did notice one thing though. After the bulbs go out, there is a repeating high pitch sound. I recorded it hoping someone here might have a clue what this would point to. forgive the quality, the sound was very quiet so i had to do some amplification & noise reduction.

WoR496,
could you explain how you pulled your monitor apart. I have the same model, except mine is working but has a vertical and a horizontal line thru the display. I have pulled the stand off (4 screws) and then removed the front bezel, but am having problem pulling the 4 connectors to ccfls and then the white mylar cable.

You have a PM

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Also i failed to mention that maybe 1 out of 8 times when you turn it on, the backlights will come back on one more time for the 1-2 seconds, then shut back off and stay off. I thought it was kind of odd and should point it out.

In case that made no sense (happens) i'll map it out simple.

Power on, lights on(1-2 sec), lights off(1-2sec), lights back on(1-2sec), no more lights, power led stays blue, makes repetitive high pitch noise.

I checked the voltage regulators on the logic board and they seem to be working fine.

[jetadm123]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Another possible culprit is the CCFL controller. It's a 16-20 pin smd chip that's generally located under the power board. Please post a photo of the power board's backside. And what's the part number of the chip?

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

0Z9937GN is what it has for the ccfl controller, if you really want a pic i'll get it but its so small theres no way i could get a good pic of it.

[PlainBill]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Somewhere around retiredcaps has written an excellent tutorial on the causes of the 'two seconds to black' problem. I suggest locating it and reading it. Caps are first suspect; CCFLs and their wiring are second, transformer is third, one of the many components in the protection circuit could also be the cause.

Assisting in troubleshooting a problem like this is difficult because we depend on you to provide the hands and report the results of tests. Trying to do this without a good picture of both sides of the board is a waste of time. Note the links in my signature for directions on how to take good pictures.

PlainBill

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

**edit** 1st character was an "O" not a zero..

so the CCFL controller is OZ9937GN

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

thank you for suggesting that tutorial, looks great will try it. I got a decent picture.

[retiredcaps]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

thank you for suggesting that tutorial, looks great will try it.

Obviously, my link in post #2 is written using invisible ink!

[jetadm123]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

You can try what PlainBill suggested about the transformers. Try checking the secondaries of the inverter transformers, T1 and T2. With power off, take resistance readings across the points marked in yellow. They should be within 3% of each other.

Also, I can't locate the datasheet for the CCFL controller.

[WoR496]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

Obviously, my link in post #2 is written using invisible ink!

If i had known that what the link pertained to i might have paid more attention to its contents i thought it was supposed to be rules for the fourms but i didn't see any ( just skimmed over) so i didn't know that it was a link to your guide.. sorry..

[romansroad]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

As to checking the ccfl's with a DMM...it wont work. The secondary check on the xformer is a good idea but in my experience, a toasted xformer will overheat the board a bit and yellow around it on the PCB. Anything that keeps you from having to open the screen is worth it!

[alexanna]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

As to checking the ccfl's with a DMM...it wont work. The secondary check on the xformer is a good idea but in my experience, a toasted xformer will overheat the board a bit and yellow around it on the PCB. Anything that keeps you from having to open the screen is worth it!

Would you reword or explain in a different way the post, I am totally confused of what you're trying to say.
Al.

[PlainBill]

Re: Dell SE198WFPf - Backlights go off after 2 seconds

As to checking the ccfl's with a DMM...it wont work. The secondary check on the xformer is a good idea but in my experience, a toasted xformer will overheat the board a bit and yellow around it on the PCB. Anything that keeps you from having to open the screen is worth it!

It depends. I've seen some that showed up clearly with a resistance check AND ringing, but the transformer looked perfect. And there was a picture posted recently with obvious physical damage to a transformer. I'd say it depends on how close the tolerances of the protection circuit is.

PlainBill