Diagnosing Black Screen LCD - Working iMac

Question

iMac Intel 27" EMC 2429

Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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mod_builder @mod_builder

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Опубликовано: 9 мар 2020 г.

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Diagnosing Black Screen LCD - Working iMac

I would like to diagnose the iMac 2011 which I got from a friend.

The iMac seems to be working as I hear the chime at startup. The display appear to be black. I did the following:

Checked display in a dark room : - nothing
Shine a light to the display :- no picture
Checked inverter of the LCD with voltmeter ": work fine

Now from here there are different possibilities as follows:

Broken LVDS connector at the logic board
Broken LED strip inside LCD
Bad LVDS connector cable
God know what exactly

So I want to begin with LVDS connector at the logic board. Where can I find the schematic of output pins and corresponding volts LVDS sends out to LVDS cable? Can this be checked with volt meter when iMac is on?

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mayer @mayer

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Опубликовано: 9 мар 2020 г.

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First is to know the history on this model.

Check on the bottom of your stand and see if your machines serial number ends in one of these:

DHJQ, DHJW, DL8Q, DNGH, DNJ9, or DMW8

DPM1, DPM2, DPNV, DNY0, DRVP, DY6F, F610
If so your problem most likely will be a defective GPU.
Hook it up to an external monitor to confirm.

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Yes it ends in DHJW. I had same 2011 iMac before with defective GPU. In that case the screen turned on and showed vertical lines all over. Here the screen doesnt turn on. Maybe its missing a GPU. Could that be the case? Also I have iMac 2010's GPU lying around. Will that be compatible with this model?

9 мар 2020 г. из mod_builder

When a GPU fails you can get all kinds of different screen indication according to what part fails first, including a black screen. So you first diagnostic step should be hooking up an external monitor (a HDMI TV will work also). Also, what are the diagnostic LEDs on the logic board telling you?

9 мар 2020 г. из mayer

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Yes it ends in DHJW. I had same 2011 iMac before with defective GPU. In that case the screen turned on and showed vertical lines all over. Here the screen doesnt turn on. Maybe its missing a GPU. Could that be the case? Also I have iMac 2010's GPU lying around. Will that be compatible with this model? — mod_builder
When a GPU fails you can get all kinds of different screen indication according to what part fails first, including a black screen. So you first diagnostic step should be hooking up an external monitor (a HDMI TV will work also). Also, what are the diagnostic LEDs on the logic board telling you? — mayer

iMac Intel 27" EMC 2429

Diagnosing Black Screen LCD - Working iMac

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