iMac 4k 2019 not detecting external monitor

Question

Level 1

8 points

iMac 4k 2019 not detecting external monitor

I have an iMac 21 inch, 4k 2019 model.

It doesn't detect my Dell P2415Q (4k) monitor connected via HDMI through Apple USB-C connector. The same monitor (with the same cable and connector) works with my MacBook Pro and my iPad.

I've tried reseting the NVRAM - didn't help. Have restarted a few times, tried other connectors with no relief (even though all combinations work with my MacBook Pro and iPad).

A few deeper thoughts: Is it a limitation of the USB-C/thunderbolt port? I currently do not have a connector with legacy USB to check, unfortunately. Is it possible to check if the USB at least got signals of my monitor?

All help appreciated.

iMac 21.5″, macOS 11.1

Posted on Jan 12, 2021 12:36 AM

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Answer 1

rkaufmann87

Level 10

148,822 points

Jan 14, 2021 9:21 AM in response to srinathrads

Did you restart in Safe Mode?

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Answer 2

rkaufmann87

Level 10

148,822 points

Jan 14, 2021 8:35 AM in response to srinathrads

It appears you are using an adapter, however please note that not all adapters are built to the same quality. Please use a high quality one such as https://www.apple.com/shop/product/HKQ22ZM/A/belkin-usb-c-to-hdmi-adapter?fnode=53e256a1b970c62b98bf775f03d76cd756ad69eeef2c2843f014886bce16c555bfdc55830b07ee3a860e67d75c02b1aa5c54b001ce89bdb72fd20f55e1f97128eac06006a2db0a2fe3390a5513b7036b89827be3cf79d754dcfadc3730a6b147

However, before going to that expense. Please try resetting the NVRAM with all wired external peripherals disconnected (displays, external HD, printers, scanners etc...) and also please try restarting in Safe Mode.

NVRAM Reset & Safe Mode Reset instructions

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Answer 3

Jan 13, 2021 4:30 PM in response to srinathrads

Hello srinathrads,

Thanks for choosing the Apple Support Communities. If we understand correctly, you are unable to connect a monitor to your iMac. We can understand why you'd reach out for a solution.

Here is a resource that can help.

Get help with video issues on external displays connected to your Mac

Cheers!

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Answer 4

jdo_apple

Community Specialist

Jan 14, 2021 8:00 AM in response to srinathrads

Thanks for the reply srinathrads,

According to your specs, you would want to use an adaptor to connect an external display. Info on that can be found below.

iMac - Technical Specifications

Two Thunderbolt 3 (USB-C) ports with support for:

DisplayPort
Thunderbolt (up to 40Gb/s)
USB 3.1 Gen 2 (up to 10Gb/s)
Thunderbolt 2, HDMI, DVI, and VGA supported using adapters (sold separately)

Are you using any of these adaptors?

Cheers!

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Answer 5

srinathrads Author

Level 1

8 points

Jan 14, 2021 8:37 AM in response to jdo_apple

Hi @jdo_apple,

Thanks for your response. I am indeed using a Apple USB C adapter.

The model number is A2119, I believe it is called a Digital AV Multiport adapter - it consists of one USB B type, one HDMI and one USB C slot as inputs and connects to the iMac via USB C.

I tried a system_profiler command (somewhat like lsusb from Linux) I found on the internet to know that the adapter is indeed getting connected; the adapter worked for a USB B pen drive that I inserted in it as well.

Im really struggling without being able to use my new 4k external monitor :(

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Answer 6

srinathrads Author

Level 1

8 points

Jan 14, 2021 8:52 AM in response to rkaufmann87

Hi @rkaufmann87,

I’m using an Apple adapter. I’ve mentioned it’s details in another reply - it is an A2119 model. It will be concerning for me if Apple made products that don’t work as advertised.

Ive also reset the NVRAM, as mentioned with no luck.

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Answer 7

srinathrads Author

Level 1

8 points

Feb 1, 2021 3:52 AM in response to rkaufmann87

Unfortunately AppleCare (India) is a pseudo thing. They only ask for my iMac to be given to the store after which they will reinstall software (which I can do myself) and test with a monitor that the shop has. They will not even entertain my 4k monitor which works brilliantly well with my MacBook Pro. Obviously, I did not go ahead with it since a time machine restore, no matter how good, destroys quite a bit of my configuration (dot files).

I've tried it with other adapters as well - all of them seem to work with my MacBook Pro, but not my iMac :(. I just need to know if this is a software issue (in which case, I will go through the crazy path of cleaning my hard disks and starting fresh) or if this is a hardware issue. The same adapter works for the USB slot, just not the monitor...

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