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Old 04-23-2018, 03:35 PM   #1
dcdcc
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Default Dell U2413 turning off

I recently bought a used Dell U2413 monitor. All is going well until after a few days, the monitor started to shut down on its own. This would happen 30mins to an hour after turning it on -- the behavior is like it's pulled from the AC plug -- no power LED, and pressing the power button does not work. It would then take a few minutes for it to turn back on on its own. Sometimes, it would shut off again within 5mins after turning back on. I noticed that the room temperatt
ure contributes to the issue. When used in a cold room/environment, the monitor works fine. Also, the monitor has four usb ports, with power coming form the main power supply circuit, and one of the ports outputs "1.5Amax" and "supports BC 1.2 compliance charging devices" as stated form the manual. As part of my trouble shooting, once the monitor turns off, I plug a usb device on each port to check for power. All three ports have power, even with the monitos' power LED out, but when I plug a device to the "1.5A" usb port, the monitor somehow turns back on, and shuts off as soon as I unplug the usb device from the said port.

I've taken a look at the power supply board and no visible signs of burnt components, bad solder joints, or bulging capacitors. Though, I've read that some caps may still be going bad even without showing physical symptoms.

Do you guys have an idea what component could be at fault here? I'm slowly leaning towards replacing all caps, but I'm still having doubts as I don't have concrete proof yet.
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Old 04-23-2018, 08:14 PM   #2
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Default Re: Dell U2413 turning off

Took a couple of images of the disassembly and board, for those looking for references, or who might encounter the same issues:

The caps are a mixture of CapXon, Sus'con, and Elite caps, not sure if they're reliable though.
Attached Images
File Type: jpg IMG_1093.jpg (424.3 KB, 4 views)
File Type: jpg IMG_1099.jpg (305.8 KB, 4 views)
File Type: jpg IMG_1105.jpg (484.3 KB, 6 views)
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File Type: jpg IMG_1120.jpg (618.1 KB, 9 views)
File Type: jpg IMG_1121.jpg (699.4 KB, 6 views)
File Type: jpg IMG_1122.jpg (726.7 KB, 7 views)
File Type: jpg IMG_1126.jpg (304.6 KB, 6 views)
File Type: jpg IMG_1128.jpg (361.8 KB, 6 views)
File Type: jpg IMG_1129.jpg (375.7 KB, 4 views)
File Type: jpg IMG_1130.jpg (338.1 KB, 5 views)
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Old 04-23-2018, 09:50 PM   #3
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Default Re: Dell U2413 turning off

I also uploaded a video to show the issue:
https://youtu.be/rC2FBfbaFmI

(I can't seem to edit my previous posts)
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Old 04-24-2018, 07:12 AM   #4
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Default Re: Dell U2413 turning off

Try again after disconnecting the USB daughter board.
Also if possible, measure voltage on all pins of the power supply connector while the monitor is off, while it is on, and after it has shut down by itself.

I don't think there is any service manual/schematics available for this one and I don't see any labelling on the power supply connector so you'll have to compare between working and non-working state.
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Old 04-24-2018, 07:26 AM   #5
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Default Re: Dell U2413 turning off

Quote:
Originally Posted by piernov View Post
Try again after disconnecting the USB daughter board.
Also if possible, measure voltage on all pins of the power supply connector while the monitor is off, while it is on, and after it has shut down by itself.

I don't think there is any service manual/schematics available for this one and I don't see any labelling on the power supply connector so you'll have to compare between working and non-working state.
I tried disconnecting the side usb board -- no luck. I've yet to check the power supply pins, though it sucks that there's no labelling on the board.
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Old 04-24-2018, 10:04 AM   #6
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Default Re: Dell U2413 turning off

Can we see good clear straight shot high res pictures of the whole top and bottom side of the power supply board?
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Basic LCD TV and Monitor troubleshooting guides.
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Inverter testing using old CFL:
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Old 04-26-2018, 02:48 AM   #7
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Default Re: Dell U2413 turning off

Quote:
Originally Posted by budm View Post
Can we see good clear straight shot high res pictures of the whole top and bottom side of the power supply board?
You can check the images I've attached below. Hope this helps
Attached Images
File Type: jpg IMG_1146.jpg (849.5 KB, 10 views)
File Type: jpg IMG_1145.jpg (856.2 KB, 5 views)
File Type: jpg IMG_1137.jpg (639.3 KB, 6 views)
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Old 04-26-2018, 01:44 PM   #8
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Default Re: Dell U2413 turning off

Check the Voltages when missing and when it does not work, see marked pictures.
The DC Voltage measured between the two legs of the main filter cap in the host side should be around 380 ~ 400VDC when monitor is turned on.
Attached Images
File Type: jpg Power supply function block.jpg (2.56 MB, 16 views)
File Type: jpg Power supply outputs.jpg (1.82 MB, 8 views)
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Old 04-26-2018, 08:31 PM   #9
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Default Re: Dell U2413 turning off

So I powered up the LCD with its guts open, plugged in to a video source -- been waiting for it to turn itself off to check voltages, but it's been an hour and a half and it's still running fine. Man, this thing won't let me troubleshoot.

@budm -- voltage from the main filter cap was steady at 427VDC

Last edited by dcdcc; 04-26-2018 at 08:35 PM..
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Old 04-26-2018, 09:37 PM   #10
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Default Re: Dell U2413 turning off

427V DC, that is on the high side, may be you should check the batteries of your meter to make sure they are OK. I would expect the OVP circuit to kick in at that high PFC Voltage.
You measure right between the two legs, not from chassis GND, correct?

Last edited by budm; 04-26-2018 at 09:39 PM..
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Old 04-26-2018, 09:45 PM   #11
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Default Re: Dell U2413 turning off

Quote:
Originally Posted by budm View Post
427V DC, that is on the high side, may be you should check the batteries of your meter to make sure they are OK. I would expect the OVP circuit to kick in at that high PFC Voltage.
You measure right between the two legs, not from chassis GND, correct?

Yes, between the two cap legs.

PS. What do you mean by OVP circuit? Thanks

Last edited by dcdcc; 04-26-2018 at 09:56 PM..
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Old 04-26-2018, 09:56 PM   #12
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Default Re: Dell U2413 turning off

'OVP' = Over Voltage Protection.
Most PFC will have Low and High Voltage protection.
So at this points you need to test all those Voltages I already marked for you in the pictures. I hope you did take the Voltage readings on those points I made for you when it is working as I suggested.
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Old 04-26-2018, 11:02 PM   #13
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Default Re: Dell U2413 turning off

Update: After it turned off, I immediately put on a fan pointed towards an SB20100 (Schottky Diode, according to its datasheet, within the "main switched power supply" circuit, with its own heatsink) and just after a few seconds, the monitor turned back on.

Last edited by dcdcc; 04-26-2018 at 11:05 PM..
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Old 04-27-2018, 12:06 AM   #14
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Default Re: Dell U2413 turning off

PS1 is stable at 5.37VDC. I can't get an accurate reading for PS2 (was hovering around 2.9mV) and PS3 (hovering around 1.5mV), and now the LCD panel is not working, but the buttons do light up, and the output of the main filter cap is now only at 348VDC.

Last edited by dcdcc; 04-27-2018 at 12:41 AM..
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Old 04-27-2018, 09:21 AM   #15
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Default Re: Dell U2413 turning off

PS1 is the standby power supply, it is working that is why you are getting the button to light up.
PS2, PS3 are the main switched power supplies that require the PFC Voltage to run, but since the PFC Boosted Voltage is low so PS2/3 stay in the shutdown mode.
At this point we need to verify if the PS-ON is present or not or we can verify to see the PFC Controller IC is getting the switched Vcc to run or not.
If you look at the picture of the top side, I marked the PFC IC, we need to the P/N as printed on the top of the IC, report what ALL the prints on top of the IC, so we can look up the spec. sheet for it.
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Old 04-27-2018, 04:36 PM   #16
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Default Re: Dell U2413 turning off

It's K15A60U
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Old 04-27-2018, 08:25 PM   #17
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Default Re: Dell U2413 turning off

Quote:
Originally Posted by dcdcc View Post
It's K15A60U
That is not it.
It is the black kind of square device with 8 pins on it.
https://www.badcaps.net/forum/attach...8&d=1524771853
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Old 05-18-2018, 06:37 PM   #18
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Default Re: Dell U2413 turning off

Quote:
Originally Posted by budm View Post
That is not it.
It is the black kind of square device with 8 pins on it.
https://www.badcaps.net/forum/attach...8&d=1524771853
apologies for the late response. Been caught up at work..

The IC says:
1608B
PRCM
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