Multiple M1 iMac issues: lots of weirdness

Hey all, hope you’re doing well. I’m tearing my hair out here (and given I have the same haircut as Telly Savalas, that’s not a good thing).

Brief history: I purchased an M1 iMac June last year, a custom build in that it had 16GB of RAM. The only non-Apple software installed on it is WebEx, WhatsApp, Google Drive (), 1Password, MS Office, and Solitaire Til Dawn. () Google Drive was installed after these issues started so I doubt it’s that.

After about three weeks it started playing up. Issues were:

  1. Corruption of external USB discs, including having some become completely unusable even on other machines
  2. Sound and microphone randomly not working with both third party apps and Apple system software (solution is to reboot the Mac)
  3. Mac not waking up from energy saver display sleep (solution is to hard cycle the iMac)
  4. Mac randomly flashing a bright purple and rebooting (after much trial and error, I found that Safari windows in private mode seem to cause this)
  5. HDMI cables running from iMac to a monitor were burning hot to the touch at the remote connector after ~1 hour of use. Same cable and monitor running from a variety of other computers for multiple hours work fine with no hot HMDI connector
  6. Touch ID stopped working and the TouchID Preference item even disappeared from the Mac.

A lot of this appeared to be with power (1 and 5, maybe 4 until I figured out the cause, and maybe 3), and I tested the Mac on different circuits in my house, got one of those gadgets that measures voltage from the GPO (same issues on different circuits, no issues with voltage coming it, it was anywhere between 240V and 245V (I’m in AU, with 240V), but never any higher). I tried it for a while in a completely different house, and the issues persisted.

Apple were quite thorough in helping me troubleshoot: multiple reinstalls, zapping PRAM etc, going through the various startup diagnostic options, and even a chap from the States ringing me and walking me through all kinds of weird firmwarey stuff. Eventually Apple conceded that there did appear to be a fault with the unit and agreed to replace it. They noted that #2 was a known issue with products such as WebEx, but I had a screen recording showing where the Sound System Preference did not even recognize the inbuilt speaker and microphone and that got the Genius Bar people really scratching their heads.

So new unit arrived, and almost immediately the same issues occurred, with the exception of #6. I set up a completely fresh account which I used as my main account, and the issues persisted. So I switched back to my primary account. Summary of the issues in with the new iMac:

#1 now happens following a Poisson distribution in that things will be fine for a few weeks and then I will get multiple disc corruptions in a short space of time (3-5 days) [My mitigation: have an old Intel iMac which (mostly) can read the drives the M1 iMac refuses to mount, and copy from old physical discs. I’m doing a manual overnight backup of the external discs once per week so worst case scenario I’m only a week out, and the contents don’t really change that much anyway. I need the external drives as I move them between machines, including some which have no access to cloud services]
#2 still happens, including the absence of devices in Sound Preferences. [I’m now used to setting up WebEx sessions with clients 10 minutes before purely to test the sound and to reboot if necessary.]
#3 happens 1-2 times per week [no mitigation, but testing has shown if I leave the Energy Saver setting to off, the problem does not occur (I’ve turned this setting off for a 3 week period, and no issues)]
#4 no longer occurs because I no longer use private browsing in Safari (I tested incognito mode in Chrome for a while and it worked fine, then uninstalled Chrome)
#5 still happens. [My mitigation: I now have a tea towel I use to remove the HDMI cable from the monitor. My son suggested that I also try unplugging it from the Thunderbolt port on the iMac (which is not hot) and letting it cool down. I only use the second monitor in sessions with my clients where they are on one screen and I use a second screen to share / present].
#7 (only on the new iMac): Bluetooth is very flaky. Upon reboot, approximately 50% of the time I need to plug in the keyboard and mouse for it to work OK. The only way Bluetooth starts to work with keyboard and mouse is via another reboot (but there seems to be no pattern to this either). Intriguingly, it has no issues at all pairing with my Sony Bluetooth headphones. [My mitigation: use cabled peripherals if necessary]

It’s all getting very tiresome, and not the user experience one expects from Apple products.

Apologies for the long preamble, but I’ve got two questions for the folks here:

  1. Does anyone have any ideas what could be causing any of these issues? I mean if someone has a silver bullet for all of them, great, but even solving one of them would be a help!
  2. I can understand getting a complete lemon as a one-off, but two in a row like this seems weird. Searching online and I can’t find anything on any of these symptoms except the WebEx sound issue, so I was wondering if anyone in the TidBITS community had experienced any of the above issues.

My day job provides me with a HP laptop which is very impressive and I’m at the point now of, for the first time since 1992 (when I moved from my Amiga 2000 to a Mac) of not having an Apple computer as my main computer, and picking up the same model HP laptop and docking station. I’d really not like to go down this path, but if I can’t solve at least three of the above, I will have to do it (if only for my own sanity).

Help me TidBits community, you’re now my only hope!



Bizarre collection.

Just a quick check - did you change out the charger as well?


Wow. Have you considered an exorcism? :ghost:

It really does sound like you had a defective unit to start, and it’s not inconceivable that you got another one.

The only thing that jumps out at me is your discussion of power. An easy test that would be worthwhile no matter what would be to get an uninterruptible power supply and attach the Mac to it. That will condition the incoming power to eliminate all spikes and drops. It’s a Hail Mary, but every desktop Mac should have a UPS anyway.

What does Apple Diagnostics have to say about your replacement M1?

Good question Tommy, and thanks for taking the time to consider my situation.

I did ask Apple if that was possible, but given that the initial issues occurred whilst Melbourne was in a lockdown it wasn’t possible to do that. The new iMac has a completely new power brick, so I don’t think it was that.

Hi Simon, thanks for your question.

On both the original and the new iMac, Diagnostics comes up clean as a whistle when I run it.

I do have “Tubular Bells” in my iTunes library. Do you think I should remove it? :stuck_out_tongue_winking_eye:

That’s an interesting idea and one I will explore. I’m in a new (< 2.5 year old) house and we did specify power filtering as part of the electrics, but I guess it can’t hurt to grab an external UPS and give that a try. I should also note that so far I’ve spent an additional AUD1,000 on things such as replacement discs (for those that are fried), fancy USB hubs, power meters, etc, so this iMac is starting to feel a bit like a Nigerian mail scam in reverse! Nonetheless will go out and grab a UPS this weekend, give it a hot and report back here.

Thanks for your ideas and thoughts; happy to receive more :slight_smile:


I’m coming along late, so perhaps the situation has changed. But a few things from your posts that stuck out to me…

You tested at a completely different house, and the issues persisted. So the cause isn’t a problem with the power at your regular house. And I doubt two houses would have the same unusual power problem. So I think a UPS would be unlikely to resolve the list of issues.

Connector on second monitor being too hot to touch sounds very bad to me. (I was taught that “too hot to touch” was a simple way to communicate about and distinguish “eh just warm” from “this is very wrong” for consumer hardware.) I wonder if this could be the root cause of the other issues. For example, this part of the system might be consuming too much power, stressing the power supply and causing the rest of the system to be supplied with inadequate power. Also I think a high bandwidth connection to a monitor is capable of generating wireless interference if the signals leak - so this might be a cause of Bluetooth issues also.

You mention only using the second monitor in sessions with clients, but I can’t tell if you unplug it. I wonder if you could leave the monitor entirely unplugged for a week say, and see if the issues are reduced?

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I agree. There’s a serious hardware problem somewhere here. Data cables should not ever get “burning hot to the touch”. They should never be moving enough current to heat up beyond heat conducted from attached equipment. If they get that hot, especially if it’s hotter than the connected device, then there’s far far too much current flowing through that cable - probably a short circuit in the connector at the source of the heat.

The fact that that cable and monitor don’t get hot with other computers doesn’t necessarily mean they are OK. It may be that other computers aren’t using all of the pins on the cable. If the short circuit is crossing wires that are not used, then they won’t get hot.

Have you tried a different HDMI cable and/or display?

Hi Ashley and thanks for your input. I worded my original question ambiguously! The monitor is in rarely, and I have had weeks at a time without the second monitor experiencing the same issues…

Have tried a different display, but not cable (this iMac is the only one where I am going USB-C to HDMI). That’s a good, cheap, suggestion and I’ll grab another cable when I am next at Officeworks.

However, @ace @Simon @tommy you may all be interested in this as well… for the last week and a bit I have turned off Energy Saver, left the computer running and can report:

  1. No issues waking up from the screen saver. Suggests that there is something funky going on with Energy Saver and reactivating the screen (wish I’d tried this with the original M1 iMac but I have a strong suspicion that this would have been the same with the original one;
  2. The bluetooth issue has disappeared;
  3. (This is the weird one) The WebEx issue has also stopped happening. Have tested it with Zoom as well, and can report it’s all good.

Machine has been up for 8 days since I turned off Energy Saver, with multiple uses of WebEx and Zoom and no drop of sound. In the past when I turned off Energy Saver on the first iMac, the sound issue persisted. Be interesting to see how long this lasts… (I have had one more external disc corruption however.)

I’m not fully happy with this workaround: I’d much rather be using EnergySaver to preserve the monitor life and not use as much power. Additionally, the iMac is in the guest bedroom and we have guests coming next week, so I will need to power it down to allow them to sleep.

Thanks again for the thoughts; I’d love to continue the discussion if it doesn’t bore people! :slight_smile:


Please do keep posting until you reach a resolution!

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I used to do mac repair at apple authorized retailers. Way back when, we had a customer who was having external SCSI hard drive failures. Through multiple attempts, eventually testing his entire computer setup, we were unable to reproduce his problems. We finally scheduled an onsite service. My co-worker went to his house, sat down at his computer, looked out the window and saw a very large multi-element ham radio antenna on his neighbors house. Turns out, every time the neighbor keyed his mike, it would make the drive fail. I don’t think any FCC class device is designed to shield against a short wave 300 watt linear amp at that distance.

The moral is, You can’t rule out external interference as a possibility.

Or, your hot display cable could be caused by some kind of ground loop, so first verify that all the devices are running off the same power strip.


OK, it’s now been well over a month since I turned off Energy Saver, and have reached the conclusion that it is the root cause of my issues. I’ve had ~ 10 days in one office, and the rest of the time has been at home. The report is the same at both locations (ie the below descriptions are valid at both places I have been trying it):

  1. Corruption of external USB discs has stopped. They will suddenly be ejected for no good reason, and I get a warning about not unplugging them. The iMac will not recognize them again until I have gone through the process of plugging them into another Mac, ejecting them properly and plugging them in again to the M1 iMac. I’ve bought a new powered USB hub, so we will see if that makes a difference. But, importantly, they are not corrupting. This issue happened once at the office and twice at home over the ~ 5 weeks since the last report;
  2. Sound and microphone randomly not working with both third party apps and Apple system software. Problem completely disappeared once Energy Saver was turned off.
  3. Mac not waking up from energy saver display sleep. Problem completely disappeared once Energy Saver was turned off.
  4. Mac randomly flashing a bright purple and rebooting (after much trial and error, I found that Safari windows in private mode seem to cause this). Am now happily spending lengthy periods of time in Safari Private mode with no issues at either location. Problem completely disappeared once Energy Saver was turned off.
  5. HDMI cables running from iMac to a monitor were burning hot to the touch at the remote connector after ~1 hour of use. Same cable and monitor running from a variety of other computers for multiple hours work fine with no hot HMDI connector. Still happening. Have tried three difference cables, on two different monitors at both locations, plus a pure HDMI cable with a HDMI <-> Thunderbolt dongle. Still hot at the remote end, not hot at the iMac end. Any random selection of cable and monitor plugged into another iMac has no hot HDMI cable.
  6. Touch ID stopped working and the TouchID Preference item even disappeared from the Mac. This has been all fine since I got the replacement iMac.
  7. Bluetooth not being recognized for keyboard and mouse. Problem completely disappeared once Energy Saver was turned off.

I’ve also got one of those voltage measurement doo-hickeys and the voltage, current, etc are all within +/- 5% of what the power company should be supplying.

Just for fun, I turned on Energy Saver last week for two days (that was the plan, ended up being one day), and in that time I had the iMac not wake up from sleep, random reboots with the purple flash, and a disc ejection (although not corruption). And I lost my sound devices again. Even though I was going to run this experiment for two days, I decided after less than a day that the grief (and risk to the external HDDs) wasn’t worth it, and turned Energy Saver off again.

I am calling this one resolved for now with a known workaround of turning off Energy Saver. It’s not ideal at all, and a mate of mine here in Oz suggested that it may be because of some weirdness in a PDU in the Mac (maybe on the USB bus), but it seems weird that I would get two bad units and not have reports that the problem is more widespread.

@tommy @ace @Simon @ashley @Shamino @gingerbeardman @icho thank you all for the time you’ve taken to consider this weirdest of issues. I’m going to keep trucking along without using Energy Saver in order to keep the Mac running smoothly. And hopefully if anyone reading this is experiencing strange issues on their M1 iMac, try turning off Energy Saver… who knows!



Happy you’re happy with the workaround!

That would drive me insane.

I just got an M1 so will watch out for this.

I’m glad you found a solution, and I thank you for posting it.

Sorry to be dense, but when I search for Energy in System Preferences, it directs me to Battery, where there is no simple on-off switch. Are you referring to Screen Saver? If so, do you put the computer to sleep manually, or leave the display on? If you are referring to something else, what? Thanks.

My MBA M1 has a habit of turning the external display black for a few seconds three or four times per month, and I’d like to try your solution. (In case it triggers a thought with someone, I do not use the internal and external displays at the same time. I would guess that 70% of the time, it’s the external display. I’m running macOS 11.6.5 Big Sur, but expect to install 11.6.7 this week.)

I’m not exactly happy with the workaround… more grudgingly accepting. Really surprised that it has come to this TBH. Have appreciated your ideas!


This is the item in the system preferences I’m talking about

In Monterey, Energy Saver (top) appears only on desktop Macs, whereas on laptop Macs, you’ll get a Battery preference pane instead (bottom).

I think what @paule means with “turning Energy Saver off” is setting it so the Mac never sleeps, which is controlled by “Prevent your Mac from automatically sleeping when the display is off.” That’s in the Power Adapter screen of either Energy Saver or Battery.

To clarify, I adjusted slider so that the display is turned off after “Never”

I created a black image which is used as the screensaver, which comes on after 30 minutes.

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FWIW and “submitted for your consideration”

I found a situation where some USB2 hard drives connected through a USB3 powered hub would disconnect when my M1 Mini went to sleep. Putting these devices on a USB2 hub seemed to make the disconnects go away.

Thanks, @ace. (In Big Sur, I don’t see “Prevent your Mac […]” in the Battery section, but you have answered the question.)

Thanks. In summary, your screen saver kicks in after 30 minutes (displaying a black screen), but the screen never turns off and the Mac never goes to sleep. I think I’ve got it now.

I’m wondering again about this, about power.

Looking through, my understanding is that:

  1. Apple replaced the entire machine, including the power brick, but the issues persisted on the replacement.

  2. You’ve set the replacement machine up in two entirely different buildings - at an office for 10 days, and at home, and the same issues are present at both locations.

Do you perhaps have a mains power strip, and/or extension lead, which you’ve used with both machines, and carried to the office?