HDMI Memory Effect (or HDMI device black listing)

Spend enough time around technology and you'll eventually come across a "weird situation". Unfortunately, the weirder it gets, the less you're likely to find help online (or anywhere else for that matter). Also, when you can't find much about an issue, you start to doubt yourself.

HDMI (High Definition Multimedia Interface) is a digital connection/signal standard that handles both video and audio signals through the one cable. (Although the original versions only carried video).

Digital signals have a lot of benefits, less noise/distortion, the signals are synchonised and managed at both ends (ensure relilable delivery) and you can transmit as many as 32 channels of Audio and some extremely high resolution video signals at speeds analogue devices could never hope to compete with.

That said, HDMI has protocols (rules) that negotiate and agree to what each device is capable of handling, then once the devices agree to work in a specific way, there's ongoing management ensure no "funny business" (signal manipulation, or copying) happens.

But what happens if the rules are broken?

There's a system called "High-Bandwitdh Digital Copy Protection" (HDCP for short) that works with all popular digital connection technologies (HDMI, DVI, and Display Port) which is supposed to prevent the copying of digital content. Normally if this isn't working you'd see a "HDCP non compliance" message instead of the video content... but this isn't what I'm experiencing either. Yet there's reports of it being reported as "No signal" on some devices. Which leads me to a rather frustrating set of experiences.

So let me tell you my tale...

I've had a Mac Mini, an A/V receiver, and a projector set up for years, and it worked well enough until I started to make some changes.

Originally the setup was as follows:

• 2014 Mac Mini (a base model that I've maxed out the RAM/SSD on)
• Anthem MRX 710 receiver (HDMI 1.4b capable with 4K passthrough)
• BenQ W3000, 1080p DLP projector.
• Two HDMI 1.4 cables, one between Mac and receiver, another between receiver and projector.

Everything was fine, the projector got old, the fan ever-more noisy, I took it apart several times, cleaned out the dust, and lubricated the bearings.. but replacing the fan wasn't an option because it was a proprietary model. In early 2024, I upgraded both the projector and Mac Mini, so now the system setup was:

• Mac Mini M2 Pro
• Same Anthem MRX710 AV recevier
• Shiny Optoma UHZ45 4K laser projector
• same HDMI cables as before.

It worked well for weeks.. then my cat got up on top of the shelf.. I didn't like that, and picked her off the shelf with all those power/HDMI cords.. she complained about being "man handled" and clawed at stuff to resist... pulling the Mac-receiver HDMI cord out of the receiver's HDMI port.

I didn't know it at the time, but this was the start to an entirely new problem that I'd never seen before... and I've seen a lot as an IT guy with decades of experiences.

Naturally, I started with the obvious stuff.

1. Shut everything down. Turned off at the wall... I know how capacitors can hold a charge.
   • Note:Assume it's been turned off at the wall for several minutes, sometimes over night when I "sleep on it" during the diagnostics described below.
2. Unplug and reconnect everything, checked everything once again.
3. Start everything back up.

Got absolutely no signal.

So I shut down, and swapped the cables out for different (known-working) ones... No luck. Receiver says "no signal".

So I tried a different input port on the receiver... still no signal. I tried all the ports... nothing.

I took the liberty at this stage to reset the receiver to factory defaults, even flashed the firmware... maybe there was a glitch? No luck.

Does the receiver even work?

So I plugged a bluray player in using the same HDMI cable... worked perfectly.. on every HDMI port on the receiver.

It's a relief... but what's going on?

So I plug the old 2014 Mac Mini in... works absolutely perfectly.

Maybe the new Mac Mini is damaged?

So I plugged the new Mini straight into the projector, (bypassing the receiver) using the Mac Mini's HDMI cable... works perfectly.. but now I don't have sound beyond the projectors, in-built speakers... After more testing, it worked perfectly on all three projector HDMI input ports.

So I take the liberty here to reduce the resolution from 4K to 1080p. Naturally it works on the direct link without the receiver.

I shut everything down and reconnect the receiver... "No signal" is displayed on the receiver's display once again, even at the reduced resolution.

Ok, it's not resolution dependent...

For a laugh, I installed the old projector again, it's only 1080P capable.. but works perfectly with the receiver and new projector.

I bought a USB-C to HDMI cable adaptor, plugged the new Mac Mini (USB-C end) into the receiver's (HDMI end)... and it worked for about an hour, then the signal died. (Imagine my frustration here). I tested the adaptor cable elsewhere (in case it's faulty) and it worked perfectly. Worked solidly for a month.

When I bought the USB-C to HDMI cable adaptor, I also bought new HDMI 2.x cables... they made no difference whatsoever.

In summary, my findings for the HDMI connections are:

• New Mac Mini, receiver, and new projector combo fails. Regardless of ports or cables used.
• I can use the old (Intel) Mini with either projector attached through the receiver.
• I can use either Mac Mini with the old projector and receiver.
• I can use either Mini with either projector if I skip the receiver.
• The USB-C to HDMI adaptor worked momentarily, then stopped working on the M2. New cables don't make a difference.
• Every component/cable works in other situations.
• Resolution, refresh rates, cable, even adaptors hadn't made any difference.

At this stage, I was baffled. Any other source device worked fine, and the setup had worked originally.

I searched online for answers... I looked for ages... didn't find much of help.

I couldn't figure it out, so I literally plugged the projector into the Mac Mini directly, then connected my Fiio BTR5 (tiny but awesome headphone DAC) via bluetooth, then piped the stereo output into the receiver's analogue inputs.

It worked, I had 4K vidoe and a very nice 2 channel (stereo) sound.... which I then set the receiver to mix it up to Dolby at least. It wasn't ideal... (I like taking my DAC when out and about).. but it got the job done.

The "Hail Mary" (Or "May I have my DAC back?").

This setup went on for months, when I went out with my DAC, the sound was effectively dead (or awful), and I wasn't the only one using this setup. Cue household tension. I ended up buying Ren an upgraded DAC.

I had to travel for work, and so I grabbed new "travel hub" for my somewhat aged laptop.

I got back from work and it largely sat on the shelf... It's another USB-C hub that had an HDMI port... I saw this and thought:

"I'll give it a go"

..I honestly didn't have much hope.. it wasn't much different to the USB-C to HDMI adaptor cable had already failed, afterall.

Yet! It worked, and never failed! I didn't like tying my travel hub down to my home setup though... but our DACs were Free! (Don't say that aloud amongst strangers in Australia... "Daks" or "Dacks" are another term for trousers/shorts/even underpants). hehehe.

If you're interested, I bought my OWC "USB-C Travel Dock" from Macfixit.com.au. The link to the specific hub is:

https://www.macfixit.com.au/collections/usb-c-travel-docks/products/owc-usb-c-travel-dock-gen-2-space-gray

I was up and running again... but this is not the end of the story...

Several months went by, and I trawled the internet, thinking that I simply couldn't be alone with this ridiculous situation.

Then I found this:

https://www.cablechick.com.au/blog/no-signal-the-hdmi-memory-effect/

It described my phenomena perfectly.. and even suggested things to try.. (which if you've read this far, you'd know that I'd pretty much tried aready). It didn't solve my issue, but at least I knew I wasn't going completely mad. :-)

Fast forward to January 2025...

This, is where things get even weirder.

I'd been running off an M2 Mac Mini for my main area, and the old 2014 Mac Mini for the guest room/office. Unfortuantely, I was doing CAD work in one whenever the other was being used... and the AutoDesk team told me that Fusion stopped supporting the 2014 model. So I upgraded to a new Mac Mini M4 Pro.

Maybe my new M4 mini will work without the travel dock?

The M4 Mini... more surprises are in store:

I plugged the new M4 Mini into the AV receiver... nothing. Direct to the projector... worked fine.

AAAAAARGH!

So I plug that travel dock in, and it works perfectly, even at higher refresh rates on 4K.

The new M4 Mac mini is tiny compared to previous generations, so I get yet another "Hagabis" branded USB-C stand with various connectivity options (notably an additional 4K capable HDMI port). I was hoping to get my travel dock back. I plugged the cable into the USB-stand's HDMI port... and...

It worked! For about 2 days.. then stopped.

What the heck is going on?...

• If it's Apple silicone era Apple device.... the receiver+ new projector combination says "NOPE!"
• If it's a cheaper (sub $100 Australian) adaptor, it works for a short time, then get's permanently blocked by new projector and receiver, but each adaptor works perfectly everywhere else afterward.

• None of those original cables are involved
• Not even using ANY of the same ports
• Signals work fine in any other combination of hardware.
• Resolution still not a factor.
• Every other source device (Bluray players, Raspberry Pies, Prehistoric Windows laptop, etc), all work!

So I'm back to using the travel dock.

• I know that the whole HDMI chain impacts functionality (both up and downstream of the receiver in the middle). Changing the projector makes it work again.
• I suspect certain cheaper adaptors are close-ish to the chips in newer Apple devices. Older generations aren't blocked.
• It doesn't appear to be banning a single, specific device, but a series of chipsets or brand(s) of similar devices.
• The ports and cables all work fine in other setups.

I've read that if can use a display port (say between a computer and monitor) instead, that should solve the problem. However, most consumer A/V gear is centred around HDMI. Display ports aren't always available on cheaper computer monitors, either.

That said, it pays to check what ports each device has, and working with that.

If you have had similar experiences, please look at the Cable Chick link above, and comment there.

I hope this helps you... or at least stops you questioning your sanity when it comes to HDMI setups. If you're looking for adaptors to fix the issue, I highly recommend a quality Dock/Hub as they seem to be much more reliable. It's still cheaper than a new Mac/Receiver/Projector, that's for sure!

All the best!

Ham.