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Old 06-04-2018, 11:58 AM   #81
Joontree
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Wow, this forum really is the place to be for this kind of work. You guys were both spot on with the diagnosis. I inspected the TCon board and reseated/cleaned all the connections to it, specifically the LVDS did seem a bit out of alignment. This seems to have solved the problem, thanks for the surgical advice! Cheers

Last edited by Joontree; 06-04-2018 at 12:00 PM..
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Old 06-04-2018, 04:30 PM   #82
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Cool man! Glad you fixed the problem. @budm: great post:-)
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Old 11-08-2018, 08:20 PM   #83
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Default Re: Dell 2408WFPb / 2408WFP - No Power

FWIW, I had the failure to power up unless the main chip was heated before applying power. I ordered a replacement off of ebay which works fine. I noticed that 4 capacitors had a different brand than the failed board. 4 x 25V 100uF. C231, C229, C116 and C114.
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Old 12-14-2018, 01:18 PM   #84
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hey everyone, I know this is an old thread but this seems to be the best place to look for answers.

I recently received a 2408WFPb for free and it doesn't work. For the heck of it I tried replacing the IC701 but that didn't do anything.

I should add that like others on here, I don't see any obvious signs of failure on the board, and that I get no indication on the power LED whatsoever.

It sounds like most people on here get some power LED indication? Not sure what my problem might be.

Just wondering if this thing is too far gone.

Thanks!
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Old 12-15-2018, 06:13 PM   #85
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by yellowsnow4free View Post
Hey everyone, I know this is an old thread but this seems to be the best place to look for answers.

I recently received a 2408WFPb for free and it doesn't work. For the heck of it I tried replacing the IC701 but that didn't do anything.

I should add that like others on here, I don't see any obvious signs of failure on the board, and that I get no indication on the power LED whatsoever.

It sounds like most people on here get some power LED indication? Not sure what my problem might be.

Just wondering if this thing is too far gone.

Thanks!
Try heating the central heat sink with a hair dryer. Once it is nice and hot, pull the power cord, count to 3, replace the power cord and turn on with the power button. This usually works for me. (I have done this successfully with the case on, but is easier with the case off.)
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Old 12-15-2018, 06:51 PM   #86
yellowsnow4free
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by dbrubeck View Post
Try heating the central heat sink with a hair dryer. Once it is nice and hot, pull the power cord, count to 3, replace the power cord and turn on with the power button. This usually works for me. (I have done this successfully with the case on, but is easier with the case off.)
Thanks dbrubeck!

It sounds like you want me to first heat the heatsink with the power cable in (and plugged in?) then to count to 3, and plug the power cable back in and turn it on? Just want to confirm about having the power cable plugged in and connected to power first.

Is this a permanent fix or a temporary one? If it's temporary, what does it tell me if the hair dryer trick works? (like, what part(s) is/are bad?)

Thanks!
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Old 12-15-2018, 07:03 PM   #87
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Please read this forum carefully. It doesn't matter whether the power cable is connected or not. Heat up the heatsink and then try to power on your monitor. If the monitor works fine, I recommend to apply Sirzur's great solution with the power resistors. You can read his description and see some clear photos as well.
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Old 01-02-2020, 04:56 AM   #88
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hello, my Dell 2408 does not switch on.
I think the power supply may still be working.
On the main board there is two heat sink :
One a little smallest than the other with "straight lines" and is a little warm.
And the other is not dissipating anything apparently.
Do you think heating more this warm heatsink is usefull ?
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Old 01-02-2020, 10:31 AM   #89
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by nabla666 View Post
Hello, my Dell 2408 does not switch on.
I think the power supply may still be working.
On the main board there is two heat sink :
One a little smallest than the other with "straight lines" and is a little warm.
And the other is not dissipating anything apparently.
Do you think heating more this warm heatsink is usefull ?
Sorry my mistake, it is the central heat sink which is warm.
The smallest one is not.
( I did not find where to edit my post....)
Damned there is an "Edit" button to this post but not to the previous one...

Last edited by nabla666; 01-02-2020 at 10:33 AM..
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Old 03-02-2020, 03:47 PM   #90
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by sirzur View Post
So I wanted to post my workaround (NOT fix) for the Dell screen not [powering on. But to recap

• The fix is to heat up the heatsink on the onboard BGA chip
• Seem to imply that the BGA solder is bad, but someone had reflowed the BGA chip and that did not fix the problem
• X-ray photography shows that the BGA solder balls to be intact
• Speculation that one of the internal pins broken and only bridged with heat
• I confirmed that a hot hair dryer on the heatsink for a few minutes will subsequently allow the monitor to light up

Hack uses two resistors powered by a USB 5V source to heat up the heatsink of the BGA chip. The basics of the USB heater design are:

• 2 X 3W, 6.8 ohm connected in series to USB source
• Heat resistant sleeve where it contacts the heatsink
• V = I X R, therefore that current in the circuit is about 0.37A, below the 0.5A specification of a USB port
• Heating power = V X I = 1.8 watts between the two resistors, so I chose 3W rated resistors for adequate safety margin


Then power down the monitor at the mains and reapply power to the monitor and it should fire up. The reapplication of power is a necessary step as just heating the heatsink with power turned on to the monitor will NOT light up the screen
Thank you so much for this! My good old Dell 2408WFP is back to working with your method

For some reason the 6.8ohm resistors I bought are more like 7.5ohm, but they do work. I used a Micro USB to USB adapter cable for the power and used heatshrink. The cable can just poke out by the composite ports without cutting the plastic case. I did bend the metal shield out of the way slightly so it can't slice the cable though.

It takes about 5 minutes of heating to get the monitor from its original state of:
Power LED blinks once then turns off

to:
Power LED blinks on very quickly, then goes off, then comes back on and stays on. The Dell logo is then displayed on the screen.

I left it connected up for around an hour and the heatsink was barely hot to the touch, so it's maybe safe to leave it connected indefinitely.
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Old 08-20-2020, 07:02 PM   #91
luke9511
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hey, everyone, I found this thread via google and figured I would post here asking for help since I have the same monitor, basically when I got it,

It was working fine and then I had to unplug it from the power and when I plugged it back in I was greeted with a messy white screen and not able to switch inputs or see the OSD menu,

if I hit the side of the monitor the picture would blink like it is trying to correct itself but it does not do anything

I took it apart and checked all of the caps and none looked bulged or anything but now when I turn it on I get the green led on the power button and a black screen but I can tell the backlights are working

and if I hit the side of it there is blinks of white, so it still does kinda work but I cannot get a picture of any kind, does anyone have any ideas what the issue might be?
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Old 12-22-2020, 06:45 PM   #92
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by sirzur View Post
So I wanted to post my workaround (NOT fix) for the Dell screen not [powering on. But to recap

• The fix is to heat up the heatsink on the onboard BGA chip
• Seem to imply that the BGA solder is bad, but someone had reflowed the BGA chip and that did not fix the problem
• X-ray photography shows that the BGA solder balls to be intact
• Speculation that one of the internal pins broken and only bridged with heat
• I confirmed that a hot hair dryer on the heatsink for a few minutes will subsequently allow the monitor to light up

Hack uses two resistors powered by a USB 5V source to heat up the heatsink of the BGA chip. The basics of the USB heater design are:

• 2 X 3W, 6.8 ohm connected in series to USB source
• Heat resistant sleeve where it contacts the heatsink
• V = I X R, therefore that current in the circuit is about 0.37A, below the 0.5A specification of a USB port
• Heating power = V X I = 1.8 watts between the two resistors, so I chose 3W rated resistors for adequate safety margin

The implementation was as follows:
• Old USB cable, but doubled up the line to reduce line resistance (Data+ and Data- cable used for power and neutral respectively)
• Heat sleeves to resistors, between resistors and also from resistors
• When circuit is soldered, do a trial with a 5V source to confirm that resistors heat up
• Outer heatsink fins bent outwards to create space for resistors. Resistors in contact with heatsink and just held in place by friction.
• Ensure no bare wire contact with heat sink
• USB cable routed under boards
• Cut made in right protective stainless steel cover and also screen back cover to allow access for USB cable
• I would strongly recommend to connect power to the USB cable to confirm that the heatsink is being heated up before reassembling the monitor

Attachment 176982

Attachment 176983

Attachment 176984

I attach some photos to show final implementation. To use it, either connect the "new" USB to a 5V source (a phone charger works) for a few minutes. I find that 2-3 minutes is all that is required on mine. Alternatively, power up the monitor - despite the screen not lighting up, there is power to the USB ports which can be used to heat up the heatsink.

Then power down the monitor at the mains and reapply power to the monitor and it should fire up. The reapplication of power is a necessary step as just heating the heatsink with power turned on to the monitor will NOT light up the screen
He everyone,
This thread was already too old but since I found the material useful in my case, thought that my follow-up would be useful for someone else...

This was my case:
Whenever I unplugged my Dell 2408wfp, there was a 50% chance it wouldn't turn on with a half dim power LED. So I had to unplug and re-plug a few times to power it on.
Finally it got really bad and didn't respond to this trick and wouldn't turn on at all...

1st step: Disassembled and checked PSU: ALL RIGHT
2nd Step: Heated main CHIP to about 60'C with a Heat Gun: power LED flashed once and after half second turned on and stayed on forever. So I thought BINGO! that's it! and applied sirzur's trick to preheat the CHIP with resistors. BUT surprisingly it didn't work . It would heat the chip but it didn't power up!
3rd step:I realized that it is not the main chip that was faulty and the reason it worked with Heat Gun but not with localized Resistor Heater, was that Heat Gun heated the adjacent elements too. I started examining those elements and found out that the faulty elements are U20 & U21 chips (marked in the attached image) that were quite close to main chip and responded well to heating. So I decided to reflow them. I used Heat Gun set to 300'C without any insulation for nearby elements! (I know, I could toast capacitors beside those chips, but fortunately it didn't happen). and VOILA.

Know no matter how long the monitor remained unplugged and in what temperature the device or it's components are, it turns on like a brand new device without needing any warming or anything else...

PS: for those for whom this trick doesn't work and might want to stick with the preheating method described by sirzur, the better calculation for the resistors:

15*10ohm 1 watt resistors arranged this way:
First group them by 3 and connect them in series => result is 5* 30ohm resistor.
Then connect those 5 resistors from previous Step in parallel => result is a 6ohm resistor that draws slightly less that 1 amp connected to 5v supply.
There is a connector on the mainboard that supplies power to the USB hub with 5 pins. the two outer ones have 5v deference. You may use them without concern about current overflow cuz it is designed to supply power to the whole HUB that has 4 USB ports and three memory sluts. But you should put a switch on the way to turn the heater off afterwards.
Two important considerations:
1-Be careful when pushing resistors in the heatsink, if you damage the thin layer of insulation on the resistors you might cuz a short circuit and damage the power supply, so check the insulation between the heatsink and heater before connecting it to the power supply.
2-use some SILICON GEL to facilitate heat transfer between heatsink and resistors.
Attached Images
File Type: jpg 1.jpg (684.3 KB, 14 views)
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Old 01-27-2021, 10:57 AM   #93
wertert
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by eaarnoudse View Post
I am also trying to repair a Dell 2408WFPb. I have the same problem as mentioned in one of the previous posts. A led light that blinks one time and the monitor won't turn on. The power supply is OK, because CN701 has about 24V on the output. The reason that the inverter board doesn't power on is simple. The first black wire on CN701 is the ON/OFF signal and it's 0V.

I started to suspect the mainboard and I found a way to power up this board. It seems like there are two main sections on it. Each section has a big chip, a crystal and a voltage regulator. First, I measured the section at the side where the power supply cable comes in. The crystal has a perfect sine wave and the voltage regulator shows a perfect 1.8V. But there is no voltage on the second crystal and voltage regulator.

I heated the heatsink and the onboard chip in the first section very carefully with a hot air rework station. Then I tried to power up the monitor and it was working great again. I waited some time until the heatsink was cooled down. The monitor did not start up. I heated the heatsink and chip again and the monitor was working fine.

I think there is a cold solder joint in one of the pins of this chip. Maybe a reflow precedure will solve the problem, although this method is not very reliable. I hope this post will help other people to troubleshoot this specific problem.

Greetz,
Erwin
Hi All

Amazing that this thread from 2011? is still helping people ! I had one of these monitors which died sometime last year. Couldn't throw it away.

It's now working again thanks to the hair dryer trick ! Brilliant.

So options-wise...

- Replace the mainboard ? I've found one on ebay for £40.00 ish which seems ok.

- Never switch it off ? i.e will standby heat be enough to keep it from dying again ?

Anything I missed ?

Great result and thanks to all again

wert
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