75' long hdmi cable will not work on iMac or MacBook Pro

archiefromhowe wrote:

I bought this cable (4K Fiber Optic HDMI Cable 75FT Long, Unidirectional 2.0 High-Speed HDMI Braided Cord).

I wonder if this is the problem.

The Mac might be expecting the ability to hear back from the monitor – to identify the monitor and its capabilities. Obviously that isn't going to happen if the connection is unidirectional.

Even if the Mac was willing to put up with a unidirectional connection, you could plug the cable in backwards with the "source" plug plugged into the monitor, and the "display" plug plugged into the computer. Then nothing that the computer tried to send to the display would reach the display – the cable's "display" end would drop the data on the floor.

hcsitas wrote:

Anything over 3’ is pushing your luck with Macs. No dice, sorry.

Since this is an "active fiber optic cable," the rules might be a little different.

The Mac doesn't have to drive a signal over 25' of copper wire. It just has to drive a signal to the transceiver that is built into the end of the cable. The transceivers at either end need to be rated for whatever type and length of optical cable is available, but assuming that

• The transceivers do not draw too much power from the computer and the monitor
• Neither the computer nor the monitor expects to draw power from the other
• The transceivers support whatever version(s) of HDMI the computer and monitor speak

the 25' length of the optical cable is not necessarily a disqualifying factor.

Hmmm… archiefromhowe, that’s about the max theoretical limit for HDMI… maybe you need an active adapter as well ( see link)

https://www.amazon.ca/CLUB-3D-CAC-2504-Type-Active/dp/B078TTHWT3… other than doing a reset smc/pmu and zapping pram 3 times on startup, I got nothing… https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html

john B

I think you may be on to something here.

IIRC the macOS tries to account for DRM when sending some vids to a monitor, and if the monitor is non-compliant then the signal doesn't go.

As you posted, being the OPs cable is stated unidirectional, then no monitor could communicate its DRM compliance back to the Mac.

Have you tried a different USB-C to HDMI adapter? Does it work with another HDMI device like a monitor?

If you look at the "similar questions" below, there are several folks with your issue.

I am going to guess that the Mac is not sending the correct info back to the Mac.

They don’t, and it’s IMO that’s gonna change. Use Apple TV & Airplay, works beautifully and way better than long cable runs.

This is a user helping users with tech questions, we are not apple and apple do not read your posts here

think few users here may have dabbled with so long hdmi cables

If you wish to reach out to apple then try  Get Support (apple.com),  Contact - Official Apple Support

Or provide them with feedback Product Feedback - Apple

Similar issue here. Using MacBook Air, have 5m (196 inches) long hdmi cable, works with smaller 24" display, but doesn't work with bigger 27". Bigger display work with shorter standard length cable.. this is very strange.. tried with several displays, different brands.

saturnus2000 wrote:

Similar issue here. Using MacBook Air, have 5m (196 inches) long hdmi cable, works with smaller 24" display, but doesn't work with bigger 27". Bigger display work with shorter standard length cable.. this is very strange.. tried with several displays, different brands.

Sounds like you're using a passive copper cable – a different beast from the active fiber-optic cable that the OP was trying to use.

Could be that the length and/or quality of your cable are marginal for the greater bandwidth demands that driving the 27" display is placing on it:

24" monitors typically have resolutions of 1920x1080 or 1920x1200.

27" monitors typically have resolutions of 2560x1440 or 3840x2160.

Anything over 3’ is pushing your luck with Macs. No dice, sorry.

Yes, Windows (and Linux) PCs and a Mac are computers. That is where the similarity ends, and just because your cabling solution works on the former is no assurance it will work on the latter.

"Should" is an emotional response. That do what they do.