Power board schematic request: Dell P2412Hb

[ngth82]

Hello all -

I have a request: does anyone have a power board schematic for a Dell P2412Hb monitor?

I got this monitor for free back in May(?) 2016. The monitor backlight turns off every now and then. I've checked the caps and they don't appear to be the issue.

Sometime in mid summer, i replaced the stock LED strip with an aftermarket LED strip and backlight and have it wired to the +30V that the display generates. The aftermarket driver board has an enable pin, and that is stuck to a 3.3V line that i found. The side effect of doing that is the screen goes all white when the display is supposed to be "off" (e.g in low power mode). The monitor works great other than the white screen.

Right now, i'm looking for the service manual (and schematics, if those are floating around) so i can figure out how the stock LED strip gets controlled. Perhaps I can use the control pin to control my aftermarket LED driver board. (OR, i suppose i can debug the stock circuit better if i had the schematics )

Thanks in advance,
Thomas

PS: sorry for any ramblings -- it's almost midnight and i'm tired.

[budm]

Re: Power board schematic request: Dell P2412Hb

How about some good clear pictures how all the board? Just have to look for the BLON signal pin from the main board.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Hi Budm -

That's the main problem I have -- there is no silk screen indicating BL_ON (or similar). I'll remove the PCBs from the monitor chassis and take a few pics.

[budm]

Re: Power board schematic request: Dell P2412Hb

Just let me see good clear pictures of the board especially the power supply board top and bottom side.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Just let me see good clear pictures of the board especially the power supply board.

Please see the attached top and bottom side pic of the power supply board.


The red, black and yellow wires go off to the aftermarket driver board. Red is +30V, black is GND, the two yellow lines (the control lines) are +3.3V on PIN1 of connetor CN701.


Thanks!

[budm]

Re: Power board schematic request: Dell P2412Hb

Let me see the bottom side too. How many wires are on that connectors that goes to the main board? All the pins have wires connected, right? We just have to look for the pin that has less than 1V when monitor is Off, and more than 3vdc when monitor is on.
Your new LED driver board uses active high signal, right?

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Let me see the bottom side too. How many wires are on that connectors that goes to the main board? All the pins have wires connected, right? We just have to look for the pin that has less than 1V when monitor is Off, and more than 3vdc when monitor is on.
Your new LED driver board uses active high signal, right?

Hi budm -

Please see my previous post. I revised it to include the top and bottom side pics right after posting the topside.

Correct, the LED driver board is active high. Let me poke around that 15 pin connector and see if I can come across any other pin that fits the bill.

Thanks!
-Thomas

[budm]

Re: Power board schematic request: Dell P2412Hb

What are those two yellow wires for? How did you figure how they are connected to that pin of the connector?

[ngth82]

Re: Power board schematic request: Dell P2412Hb

The two yellow wires are the active high control signals for the external LED driver board (and looking at the external controller board, they are routed to the same net). It's some cheapo board that I bought off of eBay and it was shipped from Hong Kong. it works, but i wasn't expecting much.

I found my mistake. I was off by one pin -- I currently have it soldered to PIN 1. It should be PIN 2 which has coincident timing with the stock LED driver turning on.

PIN 1 turns on a few hundred milliseconds faster than PIN2 and is always on after you hit the power button on the monitor. Looks like PIN 2 is the BL_ON signal.

Let me go change the wiring and i'll report back.

Thanks!

[budm]

Re: Power board schematic request: Dell P2412Hb

Hmm, I wonder why they need two wires, I would think one will be for on-off, and one for dimming control.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Hmm, I wonder why they need two wires, I would think one will be for on-off, and one for dimming control.

Looks to me it's a poorly designed board. The controller is a DF6113. According to the datasheet, there is a DIM function on that controller, but it's not pinned out to the connector.

In any case - I moved the two yellow wires over to PIN2. The monitor is working great! I don't need the DIM function in anycase since the replacement kit is a little dimmer than the original LED strip. I'm just happy the free display works

Thank you!

-Thomas

[budm]

Re: Power board schematic request: Dell P2412Hb

Glad to hear you figured it out.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Thank you as well!

[RchUncleSkeleton]

Re: Power board schematic request: Dell P2412Hb

I'm having the same issue with this monitor where the backlight will randomly turn off, especially when detecting a signal, like changing users, powering on the PC, or powering on the monitor itself.

I have taken the monitor apart and checked both the video board and the power board, but the caps seem to be fine. Granted I do not have a multimeter to test properly and even then, I'd have to remove each cap to test it out of circuit.

Usually when the monitor is on, it will stay on without issue, so long as the PC is not restarted or switched to another user, causing the monitor to try to redetect the signal. Recently, it started just turning off while the system was on and not doing anything, even though the monitor was not going to sleep, since the blue power light was still on.

Any ideas what the actual issue might be? Could it be the dimming circuit causing this?

I do know that it is possible for caps to fail without showing signs, so I guess this is a possibility.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

I'm having the same issue with this monitor where the backlight will randomly turn off, especially when detecting a signal, like changing users, powering on the PC, or powering on the monitor itself.

I have taken the monitor apart and checked both the video board and the power board, but the caps seem to be fine. Granted I do not have a multimeter to test properly and even then, I'd have to remove each cap to test it out of circuit.

Usually when the monitor is on, it will stay on without issue, so long as the PC is not restarted or switched to another user, causing the monitor to try to redetect the signal. Recently, it started just turning off while the system was on and not doing anything, even though the monitor was not going to sleep, since the blue power light was still on.

Any ideas what the actual issue might be? Could it be the dimming circuit causing this?

I do know that it is possible for caps to fail without showing signs, so I guess this is a possibility.

Hey there, those are the same original symptoms for the monitor that I have. I did not end up debugging the backlight circuit as it was just much easier to purchase a replacement LED strip and inverter board. I still have the original LED strip and cables in case I ever find the time to debug it though.

[delvorak]

Re: Power board schematic request: Dell P2412Hb

I'm having the same issue with this monitor where the backlight will randomly turn off, especially when detecting a signal, like changing users, powering on the PC, or powering on the monitor itself.

I have taken the monitor apart and checked both the video board and the power board, but the caps seem to be fine. Granted I do not have a multimeter to test properly and even then, I'd have to remove each cap to test it out of circuit.

Usually when the monitor is on, it will stay on without issue, so long as the PC is not restarted or switched to another user, causing the monitor to try to redetect the signal. Recently, it started just turning off while the system was on and not doing anything, even though the monitor was not going to sleep, since the blue power light was still on.

Any ideas what the actual issue might be? Could it be the dimming circuit causing this?

I do know that it is possible for caps to fail without showing signs, so I guess this is a possibility.

I now have two P2412Hb's that are having backlight problems. The first one acts like yours, sometimes the backlight works, sometimes it doesn't. The second one, the backlight will just flash when you turn it on, but it never stays on.

On the first one, I replaced every single capacitor on the power board, and half of them on the LCD driver board, to no avail.

It seems like the longer the monitor is powered up, the less likely the backlight is to come on.

On the second monitor, the one where it never comes on, I tried swapping out the two boards from the first into the second. Backlight still never comes on. Swapping the electronics from the second to the first, first still behaves the same, it sometimes comes on.

This leads me to conclude that the actual problem is the LED's themselves, NOT the electronics.

I ordered this replacement LED strip:

https://www.amazon.com/gp/product/B00YCTX6HO

Once I get it and test it, I'll let you guys know if it fixes the problem or not.

Scott

[delvorak]

Re: Power board schematic request: Dell P2412Hb

Quick side note: On the second monitor, the one where the backlight only flashes, I actually tested every single LED (all 70 of them) with 3.3v, and every single one worked. So if it does end up being the LED's... I have no idea why.

[muskin]

Re: Power board schematic request: Dell P2412Hb

Hi,

I just got the same monitor for free. When it is plugged in it only shows a white back ground. The built in diagnosis does not run with all the cables disconnected, just a white screen. I have not opened it up yet. I was wondering what could be some of the things to check.

Thanks

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Hey delvorak/Scott -

Did you get your replacement LED strip?

On mine, the original LED strip works fine. I can hook it up to the lab bench supply and it runs like a champ for hours. The problem appears to be with the power supply that feeds it.

I'll see if I can take the monitor apart again and update folks. The number of responses to this thread has re-upped my curiosity. It would be really nice to get the original LED strip back into the monitor.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

Hey delvorak/Scott -

Did you get your replacement LED strip?

On mine, the original LED strip works fine. I can hook it up to the lab bench supply and it runs like a champ for hours. The problem appears to be with the power supply that feeds it.

I'll see if I can take the monitor apart again and update folks. The number of responses to this thread has re-upped my curiosity. It would be really nice to get the original LED strip back into the monitor.

Curiosity over took the best of me after i posted the the last response. I still have the original LED strip -- it has been sitting on the lab bench. I decided to hook it up and see what would happen. From what i can tell, the strip is powered from 60V on the two middle pins and is comprised of four segments.

If i press on the strip, certain areas cause one or two segments to go dim or off. I'll take a look under a microscope and see if there are bad solder joints. delvorak may be on to something.