Can anyone explain the 4 LED lights for troubleshooting?

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iMac Intel 21.5" EMC 2389

Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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asle @asle20060

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发帖于: 2015年8月20日

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Can anyone explain the 4 LED lights for troubleshooting?

imac 21" model no.A1311

Sorry for double posting my problem but I still have not seen a good answer to this. My iMac 21.5" late 2010 is booting only on external monitor. The internal is not recognized and is black. There is no crazy fan blowing and everything except the internal LCD is working.

There are 4 LEDs on the logic board by the LVDS connector

1 - lights up (power)

2- lights up

3- lights up (communicating with LCD?)

4- does not light up

The question is:

Should the LED 4 light up and then go off? I understand from what is posted here that if it is on all the time there is a problem with overheating.

If LED 4 is NOT at all lighting up, where do I start for troubleshooting?

I have changed the LVDS cable and inspected the LVDS connector on the logic board side which looks ok.

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oldturkey03 @oldturkey03 声誉积分: 782.1千 1.1千 893 2.3千 · Answer 1 · 2015-08-20T04:30:25-07:00

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oldturkey03 @oldturkey03

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asle," LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card

found, and internal LCD found.

If fourth LED is not visible after power on:

• Verify internal DisplayPort cable connections between LCD panel and logic board

• Inspect LCD display cables for cable damage

• Verify external video functionality, and according to result check the following items:

If external display works then verify/replace the LED backlight board

If external display works then verify/replace the LCD panel

If external display does not work verify/replace the logic board" sounds like a bad LCD

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Thanks @oldturkey03. So the LED 4 is not lighting up, meaning there is no communication with the LCD panel. So if I understand you correct, the GPU can still be ok - but there is no response from the LCD panel? The video card is checking for the LCD, no response, so it does not light up.

So It can be the LVDS cable (which I already replaced), - the LCD panel (which I really don't know where I can test it).

The backlight will not work if there is no detected LCD panel I guess.

I will go over all contacts again, LVDS cable.

由 asle 完成的 2015年8月21日

asle, that is the way it looks. LED 4 is the communication with the panel. Your computer seems to have trouble with that.

由 oldturkey03 完成的 2015年8月21日

I understand I have trouble with my LCD. I inspected the LVDS connector on the logic board and I can see no damage. Is there any way to check if my LCD is broken or do I just have to buy a new one to test it? I would like to find that out before buying a new LCD.

由 asle 完成的 2015年9月2日

You can prove the opposite here by plugging in an external monitor. If that shows the desktop then you've isolated it down to the LCD or the LVDS cable.

由 Dan 完成的 2015年9月2日

So if an external monitor is working then I can be assured it is not the graphics card that is damaged? Guess I will have to try to find a LCD panel for this one. They seem very expensive so I will have to balance that with the value of the iMac.

由 asle 完成的 2015年9月2日

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iMac Intel 21.5" EMC 2389

Can anyone explain the 4 LED lights for troubleshooting?

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