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Author Topic: HDMI signal drops and reconnects (Mac) - DC plz help!!1  (Read 2211 times)

nosh

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HDMI signal drops and reconnects (Mac) - DC plz help!!1
« on: October 01, 2015, 11:30:50 AM »
I run a Mac Mini connected to two displays. The first is a DVI monitor (connected via a Thunderbolt to DVI adapter) and the second is a TV, directly hooked up to the HDMI out. I mirror the display to the TV to watch movies. The TV conked off a week back and was replaced.


The problem I'm facing after changing TV sets is, when I'm using the TV with the cable box or Playstation, the computer monitor starts blinking every few seconds, a solid black screen, similar to what one sees when changing resolution.

The blinking occurs twice about a second apart, every 15-20 seconds.
Observing the display options menu, I noticed that immediately after the first blink, the menu item for the TV disappears (because the Mac can't see it) there's another blink soon after when the TV gets detected and appears on the menu. It stays that way for 15-20 seconds and then the process repeats.


I've googled around and am at a total loss, I don't even know if the culprit is the Mac or the TV.
I've played around with the power consumption options on the TV, disabled mirroring, selected the "Use as separate display" option on the Mac - none of it made any difference.

When the display is being mirrored, it doesn't blink at all, steady on both ends, so I assume the HDMI cable (10 meters) is ok. Should I opt for a 5 meter high speed cable? Totally out of ideas, the only thing that works for sure right now is to pull out the HDMI cable from the Mac every time I'm not mirroring the display but that's a pain.

Edit: If I'm using the TV for Playstation or cable and power it off (standby), the monitor keeps blinking even when the TV is on standby.

Shades

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #1 on: October 03, 2015, 08:34:00 AM »
First some generics regarding cables:
Keeping cables as short as possible is always a good strategy. After all, the longer any cable is, the more chance you have it picks up interference.
After that, keep cables that carry mains separated from cables that carry data (again, interference).
Make sure that cables aren't strained in any way, internal shielding becomes compromised and generates a lot of interference on these strains in the best case scenario. Worst case scenario is a potential fire hazard.

Over-provisioning a cable might be a good thing too. if your devices have an output of a certain resolution at a certain frequency, it is a good thing to use a cable between these devices that supports certain resolution+n and certain frequency+n.

About your situation:
From your description I gather that the Mac is the problem. It gets confused when a device is connected on its HDMI port that doesn't want the signal.

If possible, swap the TV and the monitor on the Mac. Does this change the behavior?
Check for irregular behavior between versions of HDMI standards (Wikipedia). After all, there are only 6 of those standards by now. So you might need to replace the HDMI cable anyway to better match the HDMI version(s) your devices are using.

mouser

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #2 on: October 03, 2015, 01:16:32 PM »
I have had similar strange behavior with displayport and hdmi.. there was no solution.

nosh

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #3 on: October 03, 2015, 05:51:09 PM »
Shades, the mac worked just fine with the previous TV, same settings, same cable.

Swapping the devices would require me to buy two separate adapters - one HDMI to DVI (or VGA) and a Thunderbolt to HDMI, doesn't really seem worth it.

What I ended up doing was getting an HDCP compliant 3-1 switch, it's arriving in a couple of days.

An explanation from someone who replied on another forum:
Quote
The solution for some with handshake issues was to stick a little box between the Mac and HDTV or AVR that retains the correct EDID information, fooling the Mac into thinking it still is actively connected to the display. The Gefen HDMI Detective was a popular model, here's one at Amazon that might work:

http://www.amazon.co...TMD...6Y/ref=sr_1_1?

I ordered a generic pigtail switch (before I read that reply) and not the item mentioned above. If it solves the problem, great. If not, I could use the switch to change to a null output when I'm not mirroring. If that fails too (like the box not allowing me to switch to a null output when there's a live one present) I could just manually plug the cable in and out of the switch rather than the TV or mac, till a better solution comes along.

Replacing the cable seems like the next viable option. And it's also been suggested that I put an Apple TV as an intermediary.

Thanks for the input, Shades and mouser.  :up:

mouser

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #4 on: October 03, 2015, 05:56:30 PM »
that's a clever idea -- let us know if it works.
-jesse

nosh

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #5 on: October 03, 2015, 06:06:59 PM »
Sure thing.

Shades

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #6 on: October 04, 2015, 11:36:11 AM »
My switch device comment was made in the hope that you didn't have to spent time and/or money on (a) converter(s).

There are 6 versions of the HDMI protocol and, generally speaking, it isn't hard for me to imagine that if you connect a device that sends out data using HDMI 2.0 to a device that only supports HDMI 1.1, there might be some unexpected idiosyncratic behavior on either the HDMI 2.0 device or the HDMI 1.1 device. Although backwards compatibility is implied, that does not make this necessarily true for every use case in combination with different hardware from different brands.

The answer from the other forum makes actually a lot of sense. In the days of PS/2 keyboards and mouses, you needed a special kind of KVM switch that maintained those connections, even if you selected another computer. Reconnecting to a PS/2 port after the computer was turned on and expecting everything to work was not a given and could even cause the reconnected computer to freeze.

Why the history lesson? Simply to indicate that these kind of problems are not unheard of and are actually of all era's. While the area's of application vary significantly, the (idea behind the) solution is practically the same.

4wd

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #7 on: October 04, 2015, 08:11:31 PM »
I have the same problem with a tablet when connecting to TVs via mini-HDMI -> HDMI, the TV blanks every 10-15 seconds as it tries to resync with the tablet.

Nothing can be done about it other than find a TV it doesn't happen with - as Shades mentioned, unintended consequences arise from using differing versions of the standards.

nosh

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #8 on: October 23, 2015, 03:15:55 AM »
Update:

The pigtail switch did not work

I then got this powered switch, which does work:
"Kinivo 301BN Premium 3 port High speed HDMI switch with IR wireless remote and AC Power adapter"
Kinivo-310BN-HDMI-Switch.jpgHDMI signal drops and reconnects (Mac) - DC plz help!!1

It didn't work right away, the signal didn't pass through the old HDMI cable. I had to upgrade my HDMI cable to:
"BlueRigger High Speed HDMI Cable with Ethernet - CL3 Rated for In-wall Installation - Supports 3D and Audio Return",


It's not necessary to manually switch to a null output (the device doesn't even allow it) or to power off the device when I'm using the TV for something other than mirroring the computer, the switch took care of the handshake problem and works flawlessly, no drop in video quality either. 

Thanks again to everyone who chimed in.

Edit: It just occurred to me that I hadn't tried using just the upgraded cable, without the switch. It f***** works! There's no need for the switch at all, upgrading the cable was all that was required. lol
« Last Edit: October 23, 2015, 03:32:20 AM by nosh »

mouser

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #9 on: October 23, 2015, 06:45:28 AM »
thank you for the report! useful information for the rest of us. let us know if it holds up.

nosh

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Re: HDMI signal drops and reconnects (Mac) - DC plz help!!1
« Reply #10 on: October 23, 2015, 09:00:05 AM »
I expect it to - since it's just the upgraded cable directly linking the mac to the TV (no switch involved) :)