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Thunderbolt to HDMI does not detect TV on Yosemite

I am having the same problem as a lot of people with Yosemite and and connecting to a TV/external monitor via thunderbolt to HDMI but have found a sort of a solution or at least a bit more info that might lead to someone having a eureka moment. I have a Mac Book Pro, my partner a Mac Book Air. I bought a thunderbolt to HDMI cable from eBay so my partner could plug her Air into the TV. When the cable arrived, it would not detect our LG TV from either computer. So a bit of playing around and this is what I found.


  • I plugged the cable from my MBP direct to the HDMI port on the TV and nothing, no signal detected.
  • I also tried from the MBP to the HDMI port on the amplifier of the surround sound system and again nothing.
  • However, if I plug the cable from my MBP directly to the TV HDMI and select that corresponding HDMI port on the TV initially still nothing. But if I then plug a normal hdmi-to-hdmi cable from my amplifier to the Mac Pro's HDMI port, suddenly the thunderbolt cable works and the Display Preferences sees the LGTV. I checked that the correct hdmi port was selected on the TV for the direct connection and I could even turn off my amplifier to make sure that I was not seeing the wrong signal and it still worked as long as the hdmi-to-hdmi was still connected at both ends. However, if I then unplug the HDMI cable from MBP or the amp, the thunderbolt port stops working as well and the TV displays "no signal detected".

It seems that there needs to be either a base signal or an earthing through the MacBook Pro's HDMI port for it to switch into an external monitor mode that will detect a thunderbolt to HDMI connection. This is sort of fine for my MBP as I had nothing working before but it seems a bit pointless having the HDMI cable plugged in as well as I might as well just use this in the first place. However, as my partner's Air only has a thunderbolt port and no HDMI port it still doesn't work with her MAC.

Hopefully someone will see this and have a brainwave.

MacBook Pro with Retina display, OS X Yosemite (10.10.1)

Posted on Dec 3, 2014 1:00 PM

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17 replies

Feb 7, 2017 3:58 AM in response to whereisbondy

Same problem here. New to Apple products and in fairness to them, I find HDMI testing at the best of times. I've bought a thunderbolt to HDMI adapter cable and tried it on 2 TVs with 2 different MacBook Airs. Nothing nowhere nohow. Blamed the cable and the nice seller sent another one. Same thing with one of the macbooks. Will try the other later in the week. Based on some suggestions here, I wonder would it be an idea to connect the macbook to the charger giving a certain "earthing" I'm relieved that others have this problem. A real pain.

Dec 3, 2014 2:06 PM in response to whereisbondy

A bit more playing around and I found that as above with the thunderbolt to HDMI plugged into the TV and a hdmi-to-hdmi plugged into the amp, with the amp turned off, I could get the thunderbolt to HDMI working. When I then went to the Display in System Preferences and the Arrangement pane, it was showing three displays, one for the MBP screen, one for the LG TV and one for the amp HDMI port (even though it was turned off). When I then unplugged the HDMI cable from the MBP the arrangement screen was no longer available as it only recognised the MBP screen. This was the same regardless of whether I was mirroring the displayed or had them as three separate displays.

Dec 5, 2014 9:14 PM in response to cherubsta1

No, I haven't got any further in getting it working. I was hoping that perhaps an Apple support person would see it and suggest something but I'm not sure if this is how these forums work.


I did read another post though that said that if you launch System Preferences and select Display, you can then press the option key and the Detect Displays button appear. I tried this just with the Thunderbolt to HDMI/TV connected but again it would not detect this connection.

Jan 6, 2015 3:02 PM in response to cherubsta1

Hi everyone,


I'm having this super-annoying Yosemite-can't-see-my-display-even-though-it's-RIGHT-THERE issue as well. I've trawled all the forums (as I'm sure you all have) and none of the solutions worked for me, so I'm going to try installing Mavericks on a partition and see what happens. I'll post an update here.


My computer:

MacBook Pro 2012

OS X Yosemite 10.10.1

Can't detect a BenQ monitor

Mini DisplayPort to HDMI cable.

Jan 24, 2015 12:52 PM in response to skomer09

I just received my DisplayPort to HDMI cable from Amazon. I connected my MacBook to the TV, but the MacBook does not detect an external display. The cable is a bit loose when I plug it into the DisplayPort. It's very easy to wiggle around. I'm thinking it's a defective cable, so I've started the return process with Amazon, but if anybody can offer suggestions, I would appreciate it.

Jul 12, 2015 9:31 PM in response to whereisbondy

To whereisbondy:

According to an Apple rep I called today about this same issue (MBP T Bolt or HDMI ports didn't find LG TV display), it's caused by resolution incompatibility.


If your amp amplifies video signals, that may be resolving resolution incompatibilities.


Did you try connecting your MBP HDMI to amp HDMI to TV HDMI? (without any T Bolt connected)


Also, did you try connecting your MBP or your partners MBAir TBolt to amp HDMI + amp HDMI to TV HDMI?

If that works, then you may have solved the riddle - and then I DEFINITELY want the brand/model info on your amp! (Cheaper than replacing my LG TV!)


ALSO, I have non-Apple cable & adapter & they worked MBP HDMI -Samsung TV HDMI, but T Bolts didn't connect & LG still won't connect no matter what.

Jul 12, 2015 9:54 PM in response to skomer09

To Skomer09:


Did you try installing Mavericks on a separate partition yet? If so, did it work? If not, it may be due to a security update.


My old 2008 MBP MiniDisplay Port to HDMI worked w/ my LG TV for years.


I swapped out the old 500GB hard drive for a 1 TB that I later upgraded to Yosemite & that's when the problems started.


I recently sold the 2008 MBP & before I did, I re-swapped back to the old hard drive w/ Mavericks - & it worked w/ my LG TV again!


My other MBPs both have Yosemite & neither work w/ my LG TV.


Today, an Apple rep had me test my MBP HDMI w/ a Samsung TV HDMI & that worked. Then he told me it's a resolution incompatibility issue.


Another post I read mentioned a security update for some thunder-something-or-other virus (ThunderBOLT?) is what caused the incompatibility issues.


If a Mavericks partition doesn't solve the problem, it may be that the update affects all OS X versions?


Another post suggested using Time Machine to go back to a date when your monitor worked - I'm guessing that would work if the incompatibility is due to a security update. But that might mean losing a lot of data.


And if you backed up recent data & then used Time Machine to go back to a past date, would restoring recent data also restore the unwanted security update?

Thunderbolt to HDMI does not detect TV on Yosemite

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