Dell 2408WFPb will not power up

[dbrubeck]

Hi,
I have a Dell 2408WFPb which has worked for years, but after moving it to a new location, it will no longer power up. (A couple of weeks ago it also didn't power up but eventually worked after a few tries.)

None of the capacitors or other components appear damaged.

I have posted photos of the power input board and power supply board:

https://www.dropbox.com/sh/bff8p2cqb...vEc1JZjya?dl=0

Some measurements with a multimeter:

power input board:
fuse F601 - good continuity

power supply board
input cable CN603 - 122V AC
main cap C605 - 167V DC (I read in another thread that this should read higher, might be a problem)
fuse F701 (upper right below multi cable) - good continuity.

Please let me know if you have any ideas or other test points I should check.

Thanks!

[stj]

Re: Dell 2408WFPb will not power up

small capacitors will have dried up inside.

[respenica]

Re: Dell 2408WFPb will not power up

Hi, I've repaired a model like this one. It show no power -the power led remains all the time off.
It had no problem with the power supply. I've checked several components.
I had no more ideas and as a desperate measure I make a re-flow of this control board.
I've removed the heat dissipators and with a hot air gun I made a re-flow of the main chips.
It was a surprise for me that this fixed the issue!

Hope this helps you.

Regards

Roberto

[petehall347]

Re: Dell 2408WFPb will not power up

probably not the problem but that brown cap with shrunken sleeve should be changed .

[dbrubeck]

Re: Dell 2408WFPb will not power up

probably not the problem but that brown cap with shrunken sleeve should be changed .

Looking at the brown cap carefully, I don't see any bulging or leaking at either end, so I don't see any evidence that it is the problem.

[dbrubeck]

Re: Dell 2408WFPb will not power up

Hi, I've repaired a model like this one. It show no power -the power led remains all the time off.
It had no problem with the power supply. I've checked several components.
I had no more ideas and as a desperate measure I make a re-flow of this control board.
I've removed the heat dissipators and with a hot air gun I made a re-flow of the main chips.
It was a surprise for me that this fixed the issue!

Hope this helps you.

Regards

Roberto

Roberto, thanks for the idea. Did you reflow the power supply board with the big brown cap, or the next board with the video input jacks? I might try this.

[dbrubeck]

Re: Dell 2408WFPb will not power up

I'd like to narrow down the problem by ruling in or out the power supply board (with the big brown cap). I plugged in the power, then measured the voltages on the outbound power cable (upper right on the power board photo). Power light will not turn on, but I got:

Black to
Brown 0
Red 23.5 DC
Orange 0
Yellow 23.5 DC
Green 23.5 DC
Blue 0
Purple 0
Grey 0

Does anyone know if this indicates whether the power supply is working?

I'm thinking the next step is to buy a heat gun and try to reflow the main chips on the logic board.

[respenica]

Re: Dell 2408WFPb will not power up

Roberto, thanks for the idea. Did you reflow the power supply board with the big brown cap, or the next board with the video input jacks? I might try this.

I reflow the control/logic board. Note that this reflow repairs are not very reliable. Later the same problem can appear again. It already happen to me.
Note that the power supply did not had any problem.

[budm]

Re: Dell 2408WFPb will not power up

I'd like to narrow down the problem by ruling in or out the power supply board (with the big brown cap). I plugged in the power, then measured the voltages on the outbound power cable (upper right on the power board photo). Power light will not turn on, but I got:

Black to
Brown 0
Red 23.5 DC
Orange 0
Yellow 23.5 DC
Green 23.5 DC
Blue 0
Purple 0
Grey 0

Does anyone know if this indicates whether the power supply is working?
It is just the 24V power supply, so it is running, other Voltages are generated by other boards.

I'm thinking the next step is to buy a heat gun and try to reflow the main chips on the logic board.

Black wire is not GND wire! Use the chassis GND for your meter.
https://www.badcaps.net/forum/showth...t=18189&page=3

[Relayer]

Re: Dell 2408WFPb will not power up

Hello dbrubeck,
You really need to check the main filter capacitor for ESR as well as its capacitance.
You should also check any high value resistors for them going high. Check the fusible (safety) resistors as well to see if any have gone high or open circuit.
Regards,
Relayer

[dbrubeck]

Re: Dell 2408WFPb will not power up

All,
From carefully reading the other thread, I was able to narrow down the problem.

https://www.badcaps.net/forum/showpo...8&postcount=34

By heating the big chip on the logic board to around 125 degrees (by blowing heat onto the heatsink, and measuring with an IR thermometer), I was able to get the monitor to turn on normally. After the chip cooled down, it would not turn on.

I expect that by leaving the monitor in standby, there will be enough heat generated to keep this chip warm and therefore allow the monitor to function indefinitely.

If the monitor gets turned off and cools, I should be able to use a hairdryer to boot the monitor by heating up the insides to ~125.

Let's close this thread and move further discussion into the other Dell 2408 thread.

Thanks!