Power board schematic request: Dell P2412Hb

[delvorak]

Re: Power board schematic request: Dell P2412Hb

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.

I got the new strip on Saturday, and it fixed it! I installed it in the monitor that only ever flashed (the second monitor from my above post), and once I got it reassembled, the monitor worked perfectly.

I ordered another one for my other monitor.

What i don't understand is why my backlight works for about a week on the first monitor before it stops, but if I unplug it for a while it works again for about a week.

Scott

[delvorak]

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

I'm no where close to an expert. Or novice. However in my adventures tearing down the two monitors I have, it sounds like the LCD itself isn't working in your monitor. The only thing I can suggest doing is ensuring that all of the internal connections are firmly connected. I've heard of an instance where a connection was loose.

If it isn't a connection, I'm guessing it isn't fixable unless you are an electrical engineer.

[ngth82]

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

Can you post pictures of the monitor? And also of the internals? In my adventures, i got a white screen when i hooked up the replacement backlight to the wrong location (so it would essentially be on instead of turning off when the backlight should be off) -- see the original post i made at the top of this thread.

Perhaps someone modified the screen already?

[muskin]

Re: Power board schematic request: Dell P2412Hb

ngth82, I'm working a full week this week. I get off in 2 days. I will open it up and posts some pictures.
Thanks for the reply.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

I ended up purchasing a new LED strip for $25 (shipped). I got the new strip popped back into place. The monitor works for now... time will tell i guess. The LED strip that @delvorak pointed to a few posts ago is slightly different from the one that was originally inside the monitor -- different in a good way (for once).

The original strip has 4-pad SMT LEDs and maybe 20 mil traces from the + to the - pads. Two pads served no functional purpose. The board is maybe ~40 mils thick so it's fairly flexible.

The new strip consists of 2-pad SMT LEDs. The + and the - pads are good 250mil wide copper features that provide a solid anchor.

Time will tell.

[muskin]

Re: Power board schematic request: Dell P2412Hb

I did not notice any signs of bad caps. Any idea what I should check. Screen comes on but is completely white. With the monitor cables disconnected you do not see the dell monitor screen.



Thanks
Barry

[delvorak]

Re: Power board schematic request: Dell P2412Hb

I ended up purchasing a new LED strip for $25 (shipped). I got the new strip popped back into place. The monitor works for now... time will tell i guess. The LED strip that @delvorak pointed to a few posts ago is slightly different from the one that was originally inside the monitor -- different in a good way (for once).

The original strip has 4-pad SMT LEDs and maybe 20 mil traces from the + to the - pads. Two pads served no functional purpose. The board is maybe ~40 mils thick so it's fairly flexible.

The new strip consists of 2-pad SMT LEDs. The + and the - pads are good 250mil wide copper features that provide a solid anchor.

Time will tell.

I replaced the LED strip in the second monitor, it's now up and running correctly.

Glad to hear that the new strips are slightly better than the old ones.. maybe they won't die as quickly?

[muskin]

Re: Power board schematic request: Dell P2412Hb

The logic board also sends the 5vd or 12vdc power for the T-CON board, if the voltage is not there, you
will see white/grey glowing screen only.
Not much repair you can do on the logic board unless you have the full service manual and surface
mount repair station.

so it might be the logic board..

[muskin]

Re: Power board schematic request: Dell P2412Hb

Dead T-CON bd, blown fuse. Get glowing screen only.

[muskin]

Re: Power board schematic request: Dell P2412Hb

just things im reading from the basic lcd monitor troubleshooting

[Longbow]

Re: Power board schematic request: Dell P2412Hb

You are dealing with the aging of the led's themselves here. Examination under a microscope will show that the SMD construction slowly deteriorates due to heat. The internal bonding wire can actually move around, causing the LED to work sometimes and go out on others. Since the LED's are in a string, one LED malfunction shuts off all of them. It is tempting to think of LED's as having indefinite life spans, but when they are run hot the lifetimes get rather short. In addition, the light output decreases significantly with time. This problem is seen accross all kinds of appliances that use LED backlighting.

[ngth82]

Re: Power board schematic request: Dell P2412Hb

You are dealing with the aging of the led's themselves here. Examination under a microscope will show that the SMD construction slowly deteriorates due to heat. The internal bonding wire can actually move around, causing the LED to work sometimes and go out on others. Since the LED's are in a string, one LED malfunction shuts off all of them. It is tempting to think of LED's as having indefinite life spans, but when they are run hot the lifetimes get rather short. In addition, the light output decreases significantly with time. This problem is seen accross all kinds of appliances that use LED backlighting.

Well said!

[shomi75]

Re: Power board schematic request: Dell P2412Hb

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

You should leave DIM on pin1 and ENABLE on pin2. If you put it like this , DIM function work just inverse