Computer turns on, chimes, but no display

Question

iMac Intel 21.5" EMC 2308

Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo 프로세서

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Warren Willey @warrenwilley

평판: 1

게시일: 2020년 4월 11일

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Computer turns on, chimes, but no display

Hello all,

I’m working on an iMac for a friend of mine and we’ve been trying to get this thing to work for the last couple of weeks with no luck.

Initially, the computer would turn on (fans would spin up but no chime, no display). We replaced the Pram battery with a new one and tried again but same result.

My friend purchased a refurbished logic board with CPU from Mac Parts Depot and we just installed and tried it again. This time the computer turns on, chimes, but no display. We also dont have any power from the USB ports as we attempted to connect a wired keyboard but it isn’t receiving any power.

I’m leaning towards a faulty GPU as it’s the only thing we haven’t replaced, but I’m also not having any luck finding these status LED’s that everyone talks about. Either that or none of the LEDs are illuminated.

Any help would be greatly appreciated.

Thank you.

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Dan @danj 평판: 478.9k Self employed contract worker 35 329 970 · Answer 1 · 2020-04-11T15:12:22-07:00

Look at the bottom right edge of the logic board for the tape covering them

Note: you read them to left to right straight down with the top of the display toward you!

Here’s a breakdown on what they mean:

LED #1 - Indicates that trickle voltage from power supply has been detected by logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when computer has been shut down or put to sleep. The LED will turn off only if AC power source is disconnected or power supply is faulty.

LED #2 - Indicates that logic board has detected power from power supply when computer is turned on. This LED will be ON when computer is turned on and power supply and voltage regulators are working correctly.

LED #3 - Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then video card might be installed incorrectly or need replacement. Note: LED #3 is not present on models with integrated graphics.

LED #4 - Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED 4 is ON and there is no image on display, then LCD panel, LED backlight board, or cables between might be installed incorrectly or need replacement.

Let us know what you discover.

Thank you for that Dan.

The 2 LEDs on the right are lit up once the computer is powered on. LEDs 3 and 4 do not come on. — Warren Willey
@Warren Willey - There are two versions of this system do you know if yours has an integrated GPU or a MXM board version? — Dan

iMac Intel 21.5" EMC 2308

Computer turns on, chimes, but no display

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