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Old 06-12-2017, 05:56 AM   #41
YulCmr
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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 ! Did you try to reflow the faulty chip ? I've quite the same problem.

With plugging the screen I got :
-> Green Led, Orange led, Green (flickering) slowly changing to orange.
-> No Backlight
-> Power supply Ok

Before this, it was difficult to start it up (Had to plug/unplug it multiple times). Sometimes, the screen went black for 1/2sec and back on.

The radiator of the chip you describe is warm after few minutes plugged in.

It definitely seems to be the faulty part, with HDMI connected to my laptop, the screen is recognized just when I plug it, and when the 2nd green led lights up (which seem's to be a bug because of a malfunction of the CPU of the screen) it is no more.

Hope it can help someone to find a solution ...

(Sorry If there're some mistakes, I'm french)
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Old 06-12-2017, 07:16 AM   #42
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hi YulCmr,

Yes, I reflowed the chip. But it didn't work. After cooling down the chip, the problem occurred again.

When the heatsink is cold, the monitor didn't start up in my case. Even the power led didn't light up. When you blow some hot air on the heatsink, the monitor will power up.

It's a structural problem in this monitor type and it's really annoying when manufacturers use these BGA chips in combination with lead free solder.

I am afraid your monitor is beyond repair...
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Old 06-20-2017, 01:34 PM   #43
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hi,
all finaly arrived, i change

IC601 1203P60 measured voltage between VCC and GNC 5-10V it oscilating
IC651 L6561 measured voltage between VCC and GNC 1,12V - should be around 11V???

on big capacitor is 320V stable on cables from power board used blue for ground

red 5,5 - 6,5V
yellow 5,5 - 6,5V
green 5,5 - 6,5V

screen is dark also buttons is dark, no any response any ideas?
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Old 06-20-2017, 02:35 PM   #44
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Can you post some photos? did you checl the SMD components on the other side of the board?
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Old 06-20-2017, 03:35 PM   #45
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Default Re: Dell 2408WFPb / 2408WFP - No Power

no damage visible..

forgot mention I also changed IC701 to TL431I and IC603 to MCR100-8

some pictures there:
https://www.dropbox.com/s/iya39bkzzh...32304.jpg?dl=0
https://www.dropbox.com/s/dy6wnqv5zu...32229.jpg?dl=0
https://www.dropbox.com/s/9z34pnlaxc...32634.jpg?dl=0
https://www.dropbox.com/s/xe8ef54ntyw609d/IMG_20170620_232516.jpg?dl=0
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Old 06-20-2017, 04:54 PM   #46
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

You should also check all the SMD (zener) diodes. There could be one in short circuit. What output voltage do you measure?
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Old 06-21-2017, 01:05 AM   #47
locki
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Default Re: Dell 2408WFPb / 2408WFP - No Power

this is from power board to another board CN701 connector but i am not sure where i should get ground

red 5,5 - 6,5V
yellow 5,5 - 6,5V
green 5,5 - 6,5V
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Old 06-21-2017, 01:36 AM   #48
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

When you put this board back in the monitor and fix it with the srews, then you can use the chassis for COLD ground. When you measure the other lines of CN701 with the positive lead of your voltage meter, then at least the of the lines must be around 24V. I don't know the exact value, because it's some months ago I researched this monitor.

When you don't measure this value, then something is still wrong in the primary part or secondary part of your power supply. Are all smd diodes ok (the small red parts on the other side of the board)?
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Old 06-21-2017, 03:54 AM   #49
locki
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Default Re: Dell 2408WFPb / 2408WFP - No Power

physically looked ok, also measured them and If i remember everywhere was voltage drop around 0,45-0,55V (just multimeter test) on them but i will check it when it is powered on and also zener diode voltage
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Old 06-21-2017, 04:23 AM   #50
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

ok, and try to look for shorted components. These components look physically ok too...
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Old 06-21-2017, 08:32 AM   #51
locki
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Default Re: Dell 2408WFPb / 2408WFP - No Power

D601 is damaged.. in one direction from +- measured 2200 ohms oposite -+4770 ohm... i will replace it .. it should be LL4148 types in schematic for Dell_2407_WFP_power_supply_Rev_A11_schematic_diagr am.pdf then i try measure and tshoote more
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Old 06-21-2017, 09:10 AM   #52
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Did you desolder the part first? Otherwise, the measurement can be influenced by other parts...
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Old 06-21-2017, 10:03 AM   #53
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Default Re: Dell 2408WFPb / 2408WFP - No Power

sure
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Old 06-21-2017, 01:45 PM   #54
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Default Re: Dell 2408WFPb / 2408WFP - No Power

it looks like power supply running, i can hear some little noise from 1203P60
i can measure voltages on CN701 connector ...

grey 3,24V
purple 3,2V
blue 0
green 23,17V
yellow 23,17V
orange 0
red 23,17V
brown 0,712V
NC
black 3,24V


problem was in R613 . I damaged it when i solder it .. infinite R measured

i can turn it on, and i can see low backlight but not menu etc ... so i probably fixed my power supply to state like before my mistake and short circuit ...

Last edited by locki; 06-21-2017 at 02:09 PM..
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Old 06-23-2017, 02:17 AM   #55
YulCmr
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Default Re: Dell 2408WFPb / 2408WFP - No Power

eaarnoudse,

I asked for an X-Ray photography of the BGA chip at my work. I will update this thread as soon as I can got it. I hope I'll be able to see some failed solder balls.
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Old 06-23-2017, 03:54 AM   #56
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by eaarnoudse View Post
Hi YulCmr,

manufacturers use these BGA chips in combination with lead free solder.

I am afraid your monitor is beyond repair...
I had same problem, during cold morning i must sometime few times turn of and on againt to correct initialize ... so probably i have same issue
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Old 07-03-2017, 06:18 AM   #57
YulCmr
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hi !

Back from the X-ray photography. No big deal. Every solder ball seems nice and good. Soooo .... the problem is elsewhere. I get it back today, I'll have a look to the board under a microscope.

Is it really impossible to get a service manual for this screen ? I can't find one, even a non-free version.
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Old 11-16-2017, 01:51 AM   #58
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by retiredcaps View Post
1) What is the DC voltage across that small cap (right of IC652)? Is it stable or fluctuating?

2) IC601 is likely your SMPS chip.

a) What is the part number?
b) Find the datasheet.
c) Is there DC voltage on the Vcc pin?
d) Is it stable or fluctuating?

3) I assume you have mains x 1.414 DC voltage across the large filter cap? That is 120 V AC x 1.414 roughly 165 V DC?
Good day, I had same power issue with my Dell, I opened it and this is the results. After a nice clean now the led on the power button on the bezel is ON another time, when before didn't light on.

1) Anyway, in the small caps at the right of IC652 I have voltage, fluctuating, from about 0.300v. to -0.100v.

2) the SMPS chip has this part number 1203P60. There is voltage on Vcc pin and it's fluctuating from 12.5v to 14.5v about. When I click on power button the voltage here is stable 14.5v.

PS: Here in Italy we have 220-230V. AC from the power supply line.
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Old 11-16-2017, 02:04 AM   #59
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Hi YulCmr and Locki. I read your last posts now. It's good to know that the solder balls on the BGA chip are ok after the x-ray photography, so reflowing this chip will be wasting your time... I am pretty sure now that the chip itself is faulty internally. Maybe one of the pins is internally broken. When you heat up the heatsink (and so the chip), the monitor will power on. After cooling down, the problem will be back!!!

There are more Dell monitor types that use similar chips on their mainboards and I have seen the same problem on these boards. Dell doesn't supply parts and when you try to contact them, they will never respond on your messages or call you back. It's pretty frustrating. That's why I recommend my customers nowadays to avoid buying a Dell monitor....
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Old 11-16-2017, 02:07 AM   #60
eaarnoudse
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Default Re: Dell 2408WFPb / 2408WFP - No Power

Quote:
Originally Posted by Biessea View Post
Good day, I had same power issue with my Dell, I opened it and this is the results. After a nice clean now the led on the power button on the bezel is ON another time, when before didn't light on.

1) Anyway, in the small caps at the right of IC652 I have voltage, fluctuating, from about 0.300v. to -0.100v.

2) the SMPS chip has this part number 1203P60. There is voltage on Vcc pin and it's fluctuating from 12.5v to 14.5v about. When I click on power button the voltage here is stable 14.5v.

PS: Here in Italy we have 220-230V. AC from the power supply line.
Hi Biessea,

try to heat up the heatsink on the mainboard and see whether the monitor powers on. I think you have the same problem as other forum members here.

Never buy a Dell monitor again
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