Apple LED Cinema Display 24" (A1267)

[Chungalin]

This nice 1920x1200 monitor has dead backlight. Image correctly formed on LCD but no backlight. His owner says that last days it was working it got unusually hot in the lower side.

Once opened, I detect a short mosfet (540N ?) and a short diode, plus a perforated IC [U0815] (cannot read its name as the perforation is precisely there). I don't have schematics (Apple service manual considers that nobody will repair it at component level) but I assume that [U0815] is a controller for 3 power LED drivers, one for each LED strip at the panel (LCD panel LM240WU6(SD)(A1), with 3 LED strips). Shorted mosfet and diode belong to a single power driver circuit.

I attach image with interesting spots. Damaged driver circuit is the middle one (transistor disconnected and diode already stripped).

Since [U0815] is irreplaceable to me, I'm forced to replace logic board, BUT, I'm afraid that there's something at middle LED strip that caused this failure to the driver and controller, so changing logic board would be a poor long term investment...

And then the question: how can I cheaply test each LED strip to be sure that they're OK before buying a new board? According to panel datasheet each strip needs about 60V and 350mA.

Update: after finding this identical case, I get to know that controller is a HV9982. He doesn't explain if the repair was successful. Actually, he didn't even say that he was repairing this kind of monitor!

[Porto]

Re: Apple LED Cinema Display 24" (A1267)

If your lab power bench can't reach 60v DC, maybe you can build a small circuit which inputs Mains voltage, rectify that AC to DC voltage and lower the voltage with a few 2W resistors.

I have a power supply of some monitor here which does exactly that to get the voltage from 230v DC to 90v DC; they used 3 resistors in serie to get the voltage down in steps, thus not using one big resistor, maybe for heat dissipation reason or something.

Or create something with a step-up transformer.

[budm]

Re: Apple LED Cinema Display 24" (A1267)

You should check the resistance between the chassis and each pin of that LED connector (connector not connected to the board) to see if any one of those wires going to the LED strips inside is shorted to the chassis or not.
If I remember it correctly those 3 Power MOSFETs are for the Boost converter to create the drive Voltage for the LED strings.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[Chungalin]

Re: Apple LED Cinema Display 24" (A1267)

If your lab power bench can't reach 60v DC, maybe you can build a small circuit which inputs Mains voltage, rectify that AC to DC voltage and lower the voltage with a few 2W resistors.

Or create something with a step-up transformer.

I don't think it's that easy. My lab power supply just reaches 20V. But I think that when dealing with LEDs, the important point is current, not voltage. Without intensity control, I'll damage LED strips.

Budm, I already checked for shorts. I don't detect anything in the range of 20MΩ, not even between any pin and chassis, or between any pin and each other.

[Agent24]

Re: Apple LED Cinema Display 24" (A1267)

Both. You need enough voltage to overcome the forward voltage drop of the LEDs, but also something to limit the current too.

[Chungalin]

Re: Apple LED Cinema Display 24" (A1267)

I think that my best chance is to try replacing HV9982 and then I'll have two functional LED drivers (the middle one is bad). This will allow me to test each LED strip independently and detect anomalies (overheating, low light level, etc.).

[budm]

Re: Apple LED Cinema Display 24" (A1267)

It will probably go into safety shutdown if any one of the 3 is not on, so you may only see the LEDs flash on for seconds. Probably should look at the IC spec to see how it functions.

[cheebster]

Re: Apple LED Cinema Display 24" (A1267)

Any news on this one ?

[Chungalin]

Re: Apple LED Cinema Display 24" (A1267)

Since I couldn't dessolder HV9982 with my tools, we ordered a new Logic Board (PN# 661-4823).

Replaced, monitor works fine. Lower part of LCD panel (where the LEDs are) is getting pretty hot, but I don't know what is "normal". There's a temp sensor sticked right there, so it's expected to be a hotspot. Time will tell...

[stewart710]

Re: Apple LED Cinema Display 24" (A1267)

Hi, sorry to resurrect an old thread, but I have nearly the same issue but my HV9982 doesn't look damaged at all and instead of the middle led driver circuit being affected, my problem is only with the one nearest the HV9982 at the top of the picture. The obviously burnt out components are two schottky diodes marked 238C 2100b. Marking is Secos? https://cdn.badcaps-static.com/pdfs/...cbc964e3eb.pdf

and one mosfet marked 540N 88KEG. I tested them and they are definitely shorted closed now.


These are the replacement parts I was about to order from Digikey, does anyone know if they are good replacements for the 24" Apple Cinema Display LED 2008?
IRF540NSTRLPBFCT-ND
https://cdn.badcaps-static.com/pdfs/...3d1f973e5c.pdf

SS2H10-E3/5BTGICT-ND
https://cdn.badcaps-static.com/pdfs/...94309672b8.pdf

Thanks.

[Toad555]

Hi, Is this still in progress for you Stewart?

I'm trying to repair the same screen.
Are you seeing any voltage to the LED strips at all?
If so what?

Hi, sorry to resurrect an old thread, but I have nearly the same issue but my HV9982 doesn't look damaged at all and instead of the middle led driver circuit being affected, my problem is only with the one nearest the HV9982 at the top of the picture. The obviously burnt out components are two schottky diodes marked 238C 2100b. Marking is Secos? https://cdn.badcaps-static.com/pdfs/...cbc964e3eb.pdf

and one mosfet marked 540N 88KEG. I tested them and they are definitely shorted closed now.


These are the replacement parts I was about to order from Digikey, does anyone know if they are good replacements for the 24" Apple Cinema Display LED 2008?
IRF540NSTRLPBFCT-ND
https://cdn.badcaps-static.com/pdfs/...3d1f973e5c.pdf

SS2H10-E3/5BTGICT-ND
https://cdn.badcaps-static.com/pdfs/...94309672b8.pdf

Thanks.

[zielog]

Re: Apple LED Cinema Display 24" (A1267)

Hello, I'm new to this forum. I've also got the problem you are describing. I checked the voltage at the LED driver connector. The voltage is 24.5 V. In the LG display spec it says that the voltage is above 60 V. Can any one say that the voltage is with a working display?