iMac kills CEC when connected to Vizio TV

Discussion in 'iMac' started by Makosuke, Jul 10, 2016.

  1. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Just ran across a weird problem with my 5K iMac, a miniDP to HDMI adapter, and CEC control on my Vizio P702ui-B3 (previous-generation P-series) TV. The relevant part of my home theater setup is this:

    iMac > miniDP-HDMI adapter > HDMI5 input on TV (HDMI 2.0 compatible input)
    TV <> Pioneer Receiver

    I have CEC enabled on the TV and the receiver, so the TV will feed audio back to the receiver via ARC (in addition to some control stuff). Works just fine.

    ...unless I plug the HDMI adapter into the iMac. The TV gets video and audio from the computer, as you would expect, but the TV's CEC connection with the stereo fails completely. The TV doesn't even detect the stereo, and it won't pass audio back to the receiver.

    I'm actually 90% sure I had this working at some point in the past, but it definitely isn't now, and I can't figure out why having something hooked up to one of the HDMI inputs on the TV would have any effect on the CEC connection to the receiver via a different input.

    I'm guessing that the iMac is trying to pass some CEC signals to the TV as well, but even if that's true it seems like the TV should detect both devices (or at least the iMac first), rather than none at all.

    Anybody had this happen to them? Suggestions? I kind of want to use the HDMI2.0 input on the TV for the computer instead of running the signal through the receiver, but it's obviously not an option if there's no sound passthrough available.
  2. blufrog macrumors member

    Dec 19, 2014
    I see the exact same thing! I have a Samsung TV that can see the BD player connected to my amp, as well as passing audio back to the amp via ARC.

    As soon as I plug in the iMac, everything disappears. I'm running OS X 10.11.5.

    My TV is HDMI 2.0, too. How can I get the Mac to output 4K at 60 Hz? It will only do 30 Hz (my iMac 5K is allegedly capable of it - Late 2014 model).
  3. Makosuke thread starter macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Glad it's not just my hardware. I haven't tried it under 10.11.6 yet, but I'm skeptical it will help.

    Annoyingly, in my case, I can't even run it directly to the receiver--my Pioneer, for whatever reason, does the constant flashing-to-black-screen thing, like it's losing the lock on the signal or something. Which is weird because plugged directly into the TV it's fine.

    As for the 4K/60, I have never read about someone successfully doing this under the MacOS. It's apparently possible using Windows running on Mac hardware, but the MacOS itself (at least the last time I researched it) didn't support the resolution.

    This may (probably will) change eventually, and it could be there's a hack to work around it, but let me know if you come up with anything.
  4. blufrog macrumors member

    Dec 19, 2014
    I get strange results when I plugged the iMac into the amp. At first, it worked, but at low resolution (1920x1080i).

    My amp is supposed to support 4K at 30 Hz, but when I tried to set it in the iMac, it went SIGNAL NOT COMPATIBLE.

    Now, I'm unable to use any resolution through the amp!

    When I press OPT + Display to show all resolutions, the iMac shows strange aspect ratios, and up to 7290x4000 resolution (or something silly) that just is not supported by either the amp or the TV! Very very strange! :(

    I'll keep digging to see what needs to be done to get the iMac outputting 4K at 60 Hz.
    --- Post Merged, Jul 23, 2016 ---
    I found this article which has some info:
    --- Post Merged, Jul 23, 2016 ---
    The only solution I can think of to the CEC problem regarding audio is to get a second Thunderbolt to HDMI cable and plug that in separately to the amplifier, and set it as audio output.

    Apparently no Mac supports CEC/Anynet+/etc..
  5. roadkill401 macrumors 6502


    Jan 11, 2015
    works perfectly fine with my Anthem Amp. Perhaps its a cheap amp that is having the problems.
  6. blufrog, Jul 31, 2016
    Last edited: Jul 31, 2016

    blufrog macrumors member

    Dec 19, 2014
    Hmm... this is very strange.

    In safe mode I see the CORRECT resolutions for the display. In normal mode, I apparently see SCALED resolutions for the display.

    In safe mode, I can correctly set the external display. In normal mode, regardless of setting, it forces the display to 4096x2160@24p. It does scale, but the actual resolution OS X is using is wrong, so the ends of the picture are cut off, and all resolutions listed are the wrong aspect ratio.

    It would appear then that the scaling being performed by the retina drivers are screwing with correct operation of the external display, by incorrectly detecting the maximum resolution and refresh rate of the display, and not allowing you to change the "physical" resolution.

    Is there somewhere I can edit the "real" resolution and refresh rate of the display, to force it to the correct resolution of 3840x2160@30p? If I can do this, it will work.

    Also a note for anyone looking to purchase a UHD TV: The Samsung JU6400, JU6440 and JU6445 are **NOT** able to support 4K @ 60 Hz despite what Samsung may tell you!!!!!! The TV may support HDMI 2.0 (unable to confirm) but these models are artificially limited! Needless to say, I'm not very happy at this discovery.

    This explains why Samsung are very evasive about the exact resolutions/refresh rates supported via HDMI for gaming.
    --- Post Merged, Jul 31, 2016 ---
    Read my last reply above - I think it is related.
  7. Makosuke thread starter macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    I assume you've already tried holding down the option key and clicking the "Scaled" radio button in the Displays pref pane--that usually gives you much more specific choices for an external monitor.

    If that doesn't cut it, you might try the well-known SwitchResX:

    Pretty sure it's the go-to choice for setting oddball resolutions or getting the right one when your hardware isn't auto detecting it correctly. Only problem is it's kinda pricy; searching on MacUpdate turns up at least a half dozen other alternatives, all cheaper, so you might poke around and see if any of those work for you.
  8. Irishman macrumors 68030

    Nov 2, 2006
    HDMI-CEC is - at best - a roll of the dice with a/v gear that it's designed to be compatible with. At worst, it creates problems that come and go, and makes normally smart people feel like idiots.

    Adding equipment that's not designed for it just makes your life a living hell.

    My suggestion? Turn it off on all your gear. There are other and better ways to do the things that you want to do.


  9. blufrog macrumors member

    Dec 19, 2014
    I was going to try SwitchResX later, but wanted to see if there were any "legitimate" ways to get it working first. Strange that it is OK in safe mode.
  10. Makosuke thread starter macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    That's the thing, though--I don't care much about CEC, but ARC is a necessity in my configuration, and the Mac-out is killing that, too--even with CEC off on everything.

    I need ARC in any case so I can play broadcast TV through my receiver instead of the TV's chintzy built-in speakers. The only workaround for that would be an external tuner, and I'd really rather not buy yet another box when I already have one built into the TV.

    If I plug the computer into the receiver, it doesn't work for whatever reason (I've tried two different cables)--flashes on and off. Buying a new receiver isn't an option--can't afford it, and this one otherwise works fine.

    So the only remaining option to get sound into the stereo and video into the TV is to run the computer to the TV and use ARC to get the sound back... except that doesn't work. At all.

    So the only "better ways" to do what I want to do that I can come up with are:

    1) Buy a new 7.1 receiver for several hundred dollars.
    2) Buy an external HDMI switcher and hope it solves the problem, even though the receiver has one built in.
    3) Buy a new TV for a couple grand and hope it works better.
    4) Run a two-cable kludge with HDMI video and an optical (or analog) cable carrying audio to the receiver directly, and unplug the computer if I want to watch broadcast TV.

    All of those are either expensive, add even more complexity to my HT system, kludgy, or multiples thereof.

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