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Repair guides for displays (or monitors) for computers or other devices with video output.

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Dell S2421NX Monitor not showing any signs of power.

Randomly the other day I woke up to a monitor with a black screen. Neither the power indicator light or the screens backlight come on when plugged into power. I’ve tried switching power cables to known working ones and switching outlets. Windows still recognizes that a new monitor has been plugged. I have 2 of theses monitors and the other one works just fine. I’m hoping there’s just a fuse or something I need to replace.

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Hi @dragoid22

It could be just the fuse, but if it has failed then usually there's a reason why as fuses normally don't fail of their own accord.

Below is an image showing the location of the main AC input fuse on the power board of the display.

It is a T3.15A 250V sub miniature slow blow fuse (supplier example only).

You could try replacing the fuse but don't be surprised if it blows again as soon as the power is connected or shortly afterwards. (buy 2-3 fuses, just in case)

If this happens you would need to check the power board for any obvious component damage or dry joints on the soldering side (heat marks?) that may be causing this to happen and if nothing is obvious the schematic for the board would need to be found to work out what the problem is. I couldn't find it, you may have better luck.

In the end it may be easier, given the price of the power board in the link above, to simply replace it. Search for Dell S2421NX power board to find suppliers that suit you best.

Here is the Dell S2421NX simplified service manual that shows how to disassemble it so that you can remove/check/repair or replace the power board.

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(click on image)

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How could I test to see if the power board is the issue, the fuse has continuity. So I don’t think it’s the issue.

da

@dragoid22

Without the schematics I would only be guessing but check if there are any DC voltages on any of the wires going from the power board to the mainboard.

Would suspect that they shouldn't be >40V but set the DMM for 200V DC anyway just to be sure.

Also they shouldn't be <3V DC either.

You may have some where is shows 0.1-1.0V possibly.

Check forany obvious component damage on the power board i.e. leaky blown capacitors or heat stressed components etc. Also check the underside of the board for any dry joint connections

Other than that it's just guesswork unless you want to trace the incoming power through the rectifiers and then on through the switching transformer etc to the output to the mainboard.

Hot side of the board is dangerous so be careful. There's a white border line drawn on the board showing the hot and cold sides of the circuit i.e. hot = AC and high DC volts, cold = low DC volts

da

I have swapped out the power board with one from another monitor I have and I don’t think it’s the issue upon swapping out the main board everything works so it seems like that’s the issue

da

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Dragoid22 sarà eternamente grato.
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