Dell SE198WFP - Backlight for 2 seonds, then goes out.


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Dell SE198WFP - Backlight for 2 seonds, then goes out.

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WoR496
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Nov 21, 2010, 11:02 PM

Post #1 of 21 (11444 views)
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Dell SE198WFP - Backlight for 2 seonds, then goes out.	Can't Post

Hopefully nobody minds if i ask about a monitor in here.

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.

jts1957
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Nov 22, 2010, 1:56 AM

Post #2 of 21 (11441 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Are connectors to / from boards labeled as to function? B-Plus, BRI, BLON, etc.

Power supply / Inverter, common to be combined in computer monitors, could still be bad or control board may be telling it to turn backlites off.

-------------------------
Location: Far, Far Away

(This post was edited by jts1957 on Nov 22, 2010, 1:59 AM)

WoR496
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Nov 22, 2010, 3:15 AM

Post #3 of 21 (11436 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Thank you for your response.

Unfortuantly the pins are not labled on either board where the connector goes from the powersupply/inverter board to the control/video board. Here are some pics of what i'm working with here.

http://members.cox.net/jdsanchez473/lcd/1.JPG

http://members.cox.net/jdsanchez473/lcd/2.JPG

jts1957
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Nov 22, 2010, 3:33 AM

Post #4 of 21 (11431 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Can you post a pix of quadrant of BACK of PS/Inverter where connector is?
I'd like to try following the foils from connector to electrolytics/diodes, etc.
Board part number?

-------------------------
Location: Far, Far Away

(This post was edited by jts1957 on Nov 22, 2010, 3:34 AM)

WoR496
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Nov 22, 2010, 3:46 AM

Post #5 of 21 (11428 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

I can't seem to get a good enough picture so you can trace that, but i for sure can do it tomorrow. I'll take a picture and highlight the traces and list what they connect to, or whatever info you need. I really appreciate the help :) thanks!

jts1957
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Nov 22, 2010, 4:12 AM

Post #6 of 21 (11426 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

You'll probably find one (or more) ground pins, one (or more) 12/13 volt pins, one (or more) 5 volt pins. Hopefully this will leave 2 or three pins one of which should be back light enable (BLON), another back light intensity.

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Location: Far, Far Away

WoR496
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Nov 22, 2010, 7:16 PM

Post #7 of 21 (11420 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

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. Note this is with no video source hooked up. It didn't go into standby mode which i thought was kind of odd but maybe its just that way, i really don't know lol. the led stayed blue the whole time, never went orange.'

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

Will try it with a video source and see if anything changes there.

(This post was edited by WoR496 on Nov 22, 2010, 7:33 PM)

WoR496
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Nov 22, 2010, 7:22 PM

Post #8 of 21 (11419 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

No change with source.

I did notice a slight high pitch frequency when the backlights are on but its not loud at all. I'm not sure but isn't there a "normal" amount of high freq. noise generated by inverters.

(This post was edited by WoR496 on Nov 22, 2010, 7:24 PM)

WoR496
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Nov 22, 2010, 10:23 PM

Post #9 of 21 (11413 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

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.

http://members.cox.net/...473/lcd/lcdsound.mp3

WoR496
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Nov 22, 2010, 10:50 PM

Post #10 of 21 (11411 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

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.

(This post was edited by WoR496 on Nov 22, 2010, 11:21 PM)

jts1957
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Nov 23, 2010, 1:32 AM

Post #11 of 21 (11404 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

7 wires 4 near-zero.
1) NO 12v or 13v even at regulators?
2) where's pix foil views?

-------------------------
Location: Far, Far Away

WoR496
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Nov 23, 2010, 9:00 PM

Post #12 of 21 (11398 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

No 12v anywhere that i have came across.

Had something come up here.. i resoldered the xformer leads and the ccfl connector leads and most things in between. After that the first time i powered it up it did the same thing again, 1-2 sec then dead. But the second time i powered it up it stayed alive for almost a minute. Now repeatedly i can turn it on, and get light for 30-45 sec or so, then it will kind of flicker for a couple seconds, then shut off (as in no light but led stays blue)...

I'm wondering now if it is related to heat in some way with the long delay it has now before it shuts down? but then again if it was heat i wouldn't be able to shut it off, turn it right back on and get another 30-45 sec of light out of it.

jts1957
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Nov 23, 2010, 10:06 PM

Post #13 of 21 (11395 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

There are (at least two - at 12 o'clock and 1:30pm) heat sink mounted diodes on PS/inverter that should be for the approximately 5 volt and 12 volt sources. 5 volt for scaler (logic), 12 volt for inverter.

PS/Inverter board part number(s)?

This will be my last response if no pictures of rear side of PS/Inverter posted.

-------------------------
Location: Far, Far Away

(This post was edited by jts1957 on Nov 23, 2010, 10:24 PM)

WoR496
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Nov 24, 2010, 2:42 AM

Post #14 of 21 (11391 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Board reads:

490941400000R
QLPI-017 Rev.C
2007.10.19

Has OZ9937GN CCFL controller which i can't find a datasheet for...

http://members.cox.net/...473/lcd/inv-back.jpg

Will do more poking around see if i can find the 12v

Thank you for your help :)

WoR496
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Nov 24, 2010, 3:10 AM

Post #15 of 21 (11389 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

If you mean heatsink mounted transistors then here are the readings off them, all referenced from the heatsink.

12oclock transistor - when ccfl's are working normally
1- ~3.2V
2- ~16v
3- ~3.2V

12oclock transistor -when ccfl's go out and stay out
1- Alternates between ~1.85V and ~2.35V
2- Stays at ~19V
3- Alternates between ~1.85V and ~2.35V

1:30 transistor - stays same weather ccfl's are on or off
1- 0v
2- 5v
3- 0v

jts1957
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Nov 24, 2010, 4:35 AM

Post #16 of 21 (11385 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

D854 & D85?6? is diode. Pin 1 & pin 3 are wired together (VAC), center pin 2 is cathode (VDC).

-------------------------
Location: Far, Far Away

(This post was edited by jts1957 on Nov 24, 2010, 4:36 AM)

WoR496
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Nov 24, 2010, 7:56 PM

Post #17 of 21 (11377 views)
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Re: [jts1957] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

oh sorry i thought they were transistors but yes its D854 & D856 that i got the above readings from. So i guess my readings from pins 1 & 3 are not correct above since i was measuring DC ... will do again.

(This post was edited by WoR496 on Nov 24, 2010, 8:00 PM)

WoR496
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Nov 25, 2010, 1:19 AM

Post #18 of 21 (11370 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Well it turned out to be a High voltage wire running across the top of one of the ccfl's was leaking and burnt. I removed it from the bulb, patched it up with some electrical tape (yes i know, but thats what i'm working with right now) re-soldered it and no more noise, and it stays on.

WoR496
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Nov 25, 2010, 5:29 PM

Post #19 of 21 (11362 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

Monitor is all back together and has been working great for hours, just hope my tape job holds up, prob. should have used silicone. Thank you jts1957 for assisting me with this, i greatly appreciate it.

evernn
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Dec 28, 2010, 4:09 AM

Post #20 of 21 (11270 views)
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Re: [WoR496] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

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Garfed
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Apr 8, 2011, 12:42 AM

Post #21 of 21 (11024 views)
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Re: [evernn] Dell SE198WFP - Backlight for 2 seonds, then goes out. [In reply to]	Can't Post

You can find one (or more) ground pins, one (or more) 12.13 V-pin, one (or more) 5-volt line. Hopefully this will leave two or three needles should be in a backlight allows (London) and the backlight others...
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