Thunderbolt port not working with Thunderbolt monitor

Question

Thunderbolt port not working with Thunderbolt monitor

My iMac (Retina 5K, 27-inch, Late 2015 Sierra OS) stopped displaying my 27" Thunderbolt monitor. It was working fin a few days ago, and seems to correlate with the last software update. The thunderbolt monitor works on my MacBook Pro, so it works fine AND an old dell monitor will work on my thunderbolt port with adaptor. Why isn't my thunderbolt monitor not working on my iMac? I have reset SMC and did the Command-Option-P-R many times with no luck. Any other ideas? Thanks.

iMac 27", macOS 10.12

Posted on May 27, 2019 9:44 AM

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Answer 1

May 31, 2019 3:48 AM in response to garlandphotography

Just out of curiosity, do you have an extra Thunderbolt cable?

If you do, try this, connect the Thunderbolt cable to the open port

on the Thunderbolt Display. Then plug that into the iMac and see if

that works. I actually use my TB display that way now.

Reason, it could still be the built in cable. Tolerances are pretty tight on that

connection so if they are a little off, due to wear or whatever, they can be

finicky. The built in cable on my TB display has no problem plugging into

my iMac but is quite picky on inserting it "just right" on my MacBook Pro.

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Answer 2

rkaufmann87

Level 10

148,470 points

May 27, 2019 12:14 PM in response to garlandphotography

Try another Thunderbolt cable.

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Answer 3

May 28, 2019 3:48 AM in response to garlandphotography

You didn't say whether you tried it in both Thunderbolt ports?

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Answer 4

May 30, 2019 1:12 PM in response to woodmeister50

Yes tried both. Both work attached to a VGA adapter connected to an old Dell monitor. Again, both ports work with adapter, thunderbolt monitor works on my macbook pro. The Thunderbolt monitor will not work on my imac mentioned above.

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Answer 5

Jun 1, 2019 7:21 AM in response to woodmeister50

Thanks for the reply. The thunderbolt cable is built into the

thunderbolt monitor, I really didn't want to have to but a thunderbolt

to thunderbolt cable, especially since it was working fine for at least a

year and works with macbook pro, and there is no guarantee the purchase of a thunderbolt to

thunderbolt cable will work. I will purchase one as a last resort, just

hoping to get an answer without spending.

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Answer 6

May 27, 2019 1:54 PM in response to rkaufmann87

Thanks but the thunderbolt is built into the monitor and the cable works on my MacBook Pro, so I know the cable is good, it just stopped working on my iMac.

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Thunderbolt port not working with Thunderbolt monitor

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