How to read the diagnostic LEDS on 2019 21.5" iMac

Question

iMac Intel 21.5" Retina 4K Display 2019

A2116 / 2019 / 3.6 GHz quad-core i3, 3.0 GHz 6-core i5, or 3.2 GHz 6-core i7 processor. Released March 19, 2019.

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Saul Mordaunt @saulmordau61894

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Опубликовано: 26 мая 2020 г.

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How to read the diagnostic LEDS on 2019 21.5" iMac

When reconnecting my Display after HDD upgrade I have no video. There appear to be 5 diagnostic leds 3 together then another 2 above. The top one is not lit but I’m not sure what this means…. These are images of the display connector which appears to be ok…

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Image showing solder joints added

30 мая 2020 г. из Saul Mordaunt

Hi Saul, did you fix this issue? I have exactly the same problem. 3 led’s on. 4’th is on but dimmed. 5th remains off. Curious to know if you have resolved it. Thanks, Ron

6 фев 2021 г. из Ronald Koppers

Same problem - how is it fixed?

30 мая 2023 г. из David Haight

Ich habe das selbe Problem. Hat jemand schon was gefunden?

4 окт 2024 г. из michael höppner

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Ответов (2)

Hi Saul, did you fix this issue? I have exactly the same problem. 3 led’s on. 4’th is on but dimmed. 5th remains off. Curious to know if you have resolved it. Thanks, Ron — Ronald Koppers

score 2 · Answer 1 · 2020-05-27T05:18:48-07:00

Here’s the breakdown of the onboard diagnostics for your system:

LED 1 - Power is available.

If no LED is visible:

Disconnect the power cord from the computer and wait 15 seconds to reset the power supply and LED status. Reconnect the power cord and check the LED status again.
Verify the AC source.
Verify that a known-good power cord is connected. Verify the cable connection between the AC inlet and the power supply.
Verify the cable connection between the power supply and the logic board.
Verify the power supply.

LED 1 + LED 2 - Power is available and the system is turned on.

If the second LED is not visible when the power button is pressed:

Verify that the power button is connected to the power supply.
Verify power button functionality.
Verify the cable connection between the power supply and the logic board.
Verify the power supply.
Verify the logic board.

LED 1 + LED 2 + LED 3 - Power is available, the system is turned on, and the GPU was found.

If the third LED is not visible after the system is turned on:

Verify whether the fan is running when turned on (reset SMC and NVRAM, verify backup battery voltage for proper startup). If the fan is not heard, go to the "No Startup" troubleshooting flow.

LED 1 + LED 2 + LED 3 + LED 4 - Power is available, the system is turned on, the logic board is communicating with the GPU, and the internal LCD was found.

If the fourth LED is not visible after the system is turned on:

Verify the embedded DisplayPort cable (eDP) connections between the LCD panel and the logic board.
Inspect the LCD display cables for cable damage.
Verify external video functionality and proceed according to the result:
- If an external display works, verify/replace the LCD panel.
- If an external display does not work, verify/replace the logic board.

LED 1 + LED 2 + LED 3 + LED 4 + LED 5 - Power is available, system is turned on, GPU is working, logic board is communicating with the LCD panel, and the LCD panel has turned on the LCD backlight.

If the fifth LED is not visible after the computer is turned on:

Verify the eDP cable and backlight cable connections between the LCD panel and the logic board.

Inspect the LCD display cables for cable damage.
Using a flashlight, check the following areas on the panel:
Look in the top left corner of the panel to see if there is a dim Apple logo (the Apple menu logo).
Look in the center of the panel to see if there is a login screen.
Look at the bottom of the panel to see if there is a Dock visible.
If the following items are visible, there maybe something wrong with the display cables or the logic board. Proceed to the next step.
Replace the LCD panel, check that all the LEDs are visible, and that the backlight functions. If the computer does not function after replacing the LCD panel, replace the logic board.

Interestingly LEDs 1to 4 come on whether I have the LCD connected or not?? Although LED 4 is noticeably less bright than the other 3 (whether or not the lcd is connected (with both cables) Any ideas? — Saul Mordaunt
A dim LED #4 is a problem! IT should be off with no display attached. Someone who works on these systems would be using a cable extension kit for testing which is why Apple lists out the full listing of diagnostic LED's as its assumed you have such a kit. If not you know why the last LED's are not lit as you clearly don't have the internal display connected.

Let's inspect the display connector. Take some sharp detailed images of the cable end (both sides) as well as face on as well as looking into the connector like the cable would enter. Post them here so we can see Adding images to an existing question — Dan
Thanks Dan. I greatly appreciate your taking the time to investigate this. Added to the question are photos of the connectors which appear to be undamaged to me. I simply opened up the machine to replace HDD and when reconnecting, the display, which had been working fine prior, was black... I was able to read the LED's with the display connected by peeking in the side! Also attached is an image of the LED's with no display connected ~ note the dim but illuminated 4th LED. BTW desktop appears normally on external monitor — Saul Mordaunt
Let's take one more pic I need to see the connector solder joints and the components just below the connector (along the right side looking from the front). — Dan