iMac and TV aren't detecting via Mini Displayport and HDMI

Discussion in 'iMac' started by urbankaos, Sep 7, 2011.

  1. urbankaos macrumors newbie

    Sep 7, 2011
    I have an iMac, 21.5" (late 2009 model) running OS X Lion, 10.7.1
    I have a Mini Display Port to HDMI Adapter
    I have a 4 metre HDMI to HDMI Cable

    Plugged the Mini Display Port into my iMac:

    Plugged the HDMI into it:

    Then plugged the other HDMI end into my TV:

    Switched the channel onto the HDMI 1 which the Cables plugged into
    (also tried HDMI 2) went on my iMac to detect displays, but nothing...

    what am I doing wrong?
    (first time doing this obviously)

    All plugged in but when clicking on 'Detect Displays' it just does nothing, nothing happens... and on my LG TV it just says 'No Signal' :-/

    My TV picks up the HDMI because when all is plugged in, the HDMI tab on my TV is highlighted (to click onto) but when the HDMI it taken out of the Adapter, the HDMI tab goes grey... so the TV knows the HDMI is plugged into something to use, but the iMac isn't detecting the TV, and the TV just shows 'No Signal' on the Screen....

    Im wondering could there be something wrong with the Adapter itself? but then again if something was wrong with it... the TV wouldnt know that it's actually plugged into something for the HDMI 'tab' to become highlighted....

    Or could it be OS X Lion? or the HDMI Cable, or the TV?
    I have no clue, any help would be appreciated.
  2. xkmxkmxlmx macrumors 6502a


    Apr 28, 2011
    Do you have another HDMI cable to try it out with?

    Have you tried it in a different HDMI in port on your TV?

    On some TVs, I have heard of a setting that you have to enable when trying to hook up a computer. I wonder if yours might need it.

    The fact that your mac is not picking up the signal. That might mean it is just a connection problem (either the adapter, the HDMI cable or the port on the TV itself - my HDMI 1 and 2 ports "burned out" on my last TV).

    So the fact that your TV is reading that *something* is plugged into it, but it is not getting a full signal so it displays nothing. THe Mac can't tell that it is plugged into anything, so I am betting it is on the cable/mac end.

    The only thing to suggest is keep trying with different configurations.
  3. urbankaos thread starter macrumors newbie

    Sep 7, 2011
    I haven't got another HDMI Cable no,
    but I wouldn't of though it would be the Cable or Adapter as the TV actually knows when the HDMI Cable is plugged into the Adapter.

    and i've got 2 HDMI Ports, and i've tried them both.

    and i've looked through my TV Settings, nothing on there at all about Computers, just basic things like the Screen type, Cinema, Sport etc, the Sound and so on.

    and the TV is practically brand new, had it about 2 weeks ago, never used the HDMI ports before but it's a brand new TV, and I wouldn't of thought anything would be wrong with the Adapter or Cable as the TV knows when they're plugged in, if they were not working then the TV wouldn't know.

    it's a little confusing......
  4. urbankaos thread starter macrumors newbie

    Sep 7, 2011
    I did see on alot of Websites that since upgrading to Lion, their whole 'hooking their Macs to TVs stopped working', would this be something to look into more? would upgrading to Lion affect that in any way?
  5. xkmxkmxlmx macrumors 6502a


    Apr 28, 2011
    Like I said though (and I might have been a bit confusing, I posted right when I woke up lol), teh TV might detect that it has an HDMI cable inserted even if the source is not outputting or there is trouble with one of the connections.

    For instance, I had an HDMI cable that I was using with my PS3 go bad on me. The screen just went black, but the TV and PS3 both knew that there was some sort of connection.

    Quite possible, yes. I have not had any problems at all with my setup though (Lion to 2011 Vizio). I would suggest just ordering a cheap HDMI cable at monoprice and see if that is the issue.
  6. urbankaos thread starter macrumors newbie

    Sep 7, 2011
    Well the Adapter and Cable were both cheap ones from eBay,
    about £4.99 and £5.95

    I've just ordered a branded set now from Neet,
    so going to try them, if they dont work either then obv its the TV or the iMac.
  7. urbankaos thread starter macrumors newbie

    Sep 7, 2011
    I've got my new Neet wires...

    when plugging in the Neet Adapter and Cable, the TV didnt pick up a HDMI connection,
    so i've plugged in the cheap Adapter I bought first with the Neet HDMI Cable and the TV picks up a connection, and the iMac flashes Blue a couple of times,
    but still No Signal on the TV.
  8. xkmxkmxlmx macrumors 6502a


    Apr 28, 2011
    What are you trying to play and what are you using to play it.

    What does the TV look like?

    Are you trying to "mirror" your display or use it as a second monitor.

    The blue screen is normal. Did it happen when you tried it with your initial cable setup (when you first asked about it)? It would indicate that at least your mac is picking up the second display.

    What does it say under display preferences? Can you see your TV there? Is there any weird option that is checked/unchecked?

    What cables are you using exactly?

    I use this setup and it works perfectly:

    and this adapter

    They have worked like a charm with two different imacs, a mbp and a mba.
  9. urbankaos thread starter macrumors newbie

    Sep 7, 2011
    Hey, I got it working now :)

    purchased the NEET Adapter and Cable, didnt work...
    had a replacement Adapter today, plugged it in and BAM!!!
    the iMac picked up the TV, everythings working fine :)

    my only issue is that I want the display on my TV to be like my iMac,
    regarding size, but when I change it on my TV Settings, it changes it on my iMac aswell and its stretched, is there no way I can have my iMac normal, and have the display on my TV similar but not crap quality?
  10. xkmxkmxlmx macrumors 6502a


    Apr 28, 2011
    Again, I ask, how are you outputting? Are you mirroring your screens or are you using it as a secondary?

    This is also where that "computer" setting might come in handy. Mine doesn't have it, but I do have to set how I want it to display on my TV in display preferences. For instance, my tv is 1080p, but my mac wants to force it as 720p. So I go into display prefs, find the TV and then change the res.
  11. michial macrumors 6502a


    Sep 15, 2009
    I just replaced my hp laptop which I used everyday to watch movies by plugging my hdmi into it and my panasonic plasma hdtv. It worked perfectly. I just bought a new 21.5 iMac a few days ago and a mini display to hdmi adapter from apple store and plugged the same hdmi in and it doesn't work.

    the iMac recognizes the tv brand and all in the display prefs but the iMac isn't displayed on the panny tv. I know all the cables work and the iMac recognizes it so I am not sure what is going on. I heard you have to shut off both devices first and then turn them on in a certain order is that true? Any help is appreciated.
  12. xraydoc macrumors demi-god


    Oct 9, 2005
    System Preferences -> Displays -> Arrangement -> uncheck Mirroring
  13. paganima macrumors newbie

    Apr 20, 2014
    urbankaos, could you please say what is brand of your adapter that works fine?
  14. LittleRedRiding macrumors newbie

    Feb 8, 2010
    I'm having a similar problem. My electricity ran out (i'm on a meter, it happens all the time) and when everything came back on my TV would no longer display my iMac screen. The Mac and TV know that there is an HDMI connection as when I unplug it is says 'No Cable Connection' but when plugged in the Mac flickers and the TV changes to 'No Signal'. When go to System Preferences>Displays I am just met with the iMac screen brightness options.
  15. karma3 macrumors newbie

    Dec 20, 2015
    Michial, I am having exactly the same problem you had. I have a laptop that works perfectly with my Pan. Plasma. When I hook-up my iMac through the same cords, nothing. Just a black screen on the TV. The computer recognizes the TV and my external display works fine with my iMac. Did you ever resolve your issue?

Share This Page