Dell 22" monitor backlight goes out right away.

[BlkSmth]

Re: Dell 22" monitor backlight goes out right away.

that should be the datasheet on the ic



Off-Line SMPS Failure Modes PWM Switchers and
DC-DC Converters

https://cdn.badcaps-static.com/pdfs/...68e55164c4.pdf


Replacement if needed:

http://parts.digikey.com/1/parts/623...uc3525adw.html
or here might be cheaper?

http://www.newark.com/texas-instrume...494/dp/98K1694

you can use this schematic from the link below to share with your powerboard on pages 30,31, and see flowchart on 50+

http://www.scribd.com/doc/14955876/P...0s8Fs00-Series

I know them pdf for manuals are not your model specific, but again have your board exact in them hope this helps... My first helping post

[Th3_uN1Qu3]

Re: Dell 22" monitor backlight goes out right away.

I am fighting on of these monitors, rather than boring everyone with a bunch of voltage measurements, an checks I've done I hoping someone could point me to a datasheet as how the TL4941 would work in a CCFL circuit. It is different than I am accustomed to seeing.

That's TL494, without the " 1 ". That is actually an " I ". It's one of the most popular SMPS controllers. Find where the reference voltage is connected (to positive or negative inputs of error amps). The reference is likely to be 5v in this case. Then check the voltages at the other error amp inputs, DTC and feedback pin. One of those will go high when the inverter shuts down. (The feedback pin will also go high if any of the error amps goes high, so check those first). If any of those four pins i mentioned are at the same level, or exceeding, the reference voltage, then the outputs of the 494 are shut down.

Once you've located the pin that triggers the shutdown, trace it and see what pulls it high.

[boomer9999]

Re: Dell 22" monitor backlight goes out right away.

that should be the datasheet on the ic



Off-Line SMPS Failure Modes PWM Switchers and
DC-DC Converters

https://cdn.badcaps-static.com/pdfs/...68e55164c4.pdf


Replacement if needed:

http://parts.digikey.com/1/parts/623...uc3525adw.html
or here might be cheaper?

http://www.newark.com/texas-instrume...494/dp/98K1694

you can use this schematic from the link below to share with your powerboard on pages 30,31, and see flowchart on 50+

http://www.scribd.com/doc/14955876/P...0s8Fs00-Series

I know them pdf for manuals are not your model specific, but again have your board exact in them hope this helps... My first helping post

See here:
http://en.community.dell.com/support...px?PageIndex=5

I fixed this monitor with the mod mentioned at the bottom:

[Then added a 2nd 1meg resistor in parallel with the 1st effectively making it a 500k resistor. Seems to be working great. Have had it running for several hours now....let's see how long this one lasts. Will keep fingers crossed ! ]

Monitor has been running 8hrs/day for months without issue.

Thread seems to indicate design flaw in circuit tolerances.

[Th3_uN1Qu3]

Re: Dell 22" monitor backlight goes out right away.

Thread seems to indicate design flaw in circuit tolerances.

Darn, Dell's site runs even slower than their computers do... Too bad they don't have the whole schematic so i can't figure it out entirely, but i must say this - a 1 Meg resistor looks terribly out of place in this circuit. So do a number of other values there.

They probably only did this because they used tiny SMD parts (1/10W, seriously now...) and they needed to limit their dissipation. Though, 1 meg there will dissipate 1/10W at 100 volts. The voltage on that circuit is probably 20 volts at most. So, 1 meg resistor could have been much smaller value. I call that incompetence.

[alexanna]

Re: Dell 22" monitor backlight goes out right away.

Thanks for all the good information.
Sounds like I've got my work cut out; I'll mess around with it and try to let you know what happens.

[jimboee]

Re: Dell 22" monitor backlight goes out right away.

This has been the most informative thread on this topic.
Don't know if it will fix it, but I will also try.

thanks.

[alexanna]

Re: Dell 22" monitor backlight goes out right away.

This has been the most informative thread on this topic.
Don't know if it will fix it, but I will also try.

thanks.

This is a work around that I would not recommend, with a 470K resistor substituted for the 1Meg resistor the under voltage protection is disabled.
I can't take a chance on it.

[Th3_uN1Qu3]

Re: Dell 22" monitor backlight goes out right away.

with a 470K resistor substituted for the 1Meg resistor the under voltage protection is disabled.

Do you have a full schematic by any chance?

[alexanna]

Re: Dell 22" monitor backlight goes out right away.

Do you have a full schematic by any chance?

Not on this monitor
The scribd link in one of the above posts shows the controller being used in a Hudson monitor.
This monitor is one that uses one transformer for 2 CCFLs, and it has to have both CCFLs installed to work correctly. If one CCFL failed in the future and the inverter doesn't shut down, I can see it doing some serious damage.

[Toasty]

Re: Dell 22" monitor backlight goes out right away.

Uploaded circuit in case Dell loses it.

Also see Jack Crow's pictures in thread: https://www.badcaps.net/forum/showthread.php?p=213522

.

[mdwridge]

Re: Dell 22" monitor backlight goes out right away.

I also had the same Problems with this monitor, For me the backlights turned off almost immediately after power-up. I tried the fix of removing the R821, and then they stayed on. I checked r821 in and out of circuit and it tested good, however after replacing it with a new, similar one, the screen has been running perfect since. It must have been going low ohms under load. just thought Id add that info for those who might think this resistor is good when it tests out fine with a multimeter.