27.0″

Two things … connected with a 2011 27″ iMac now installed with a fab version of MX Linux KDE that a customer will be buying next Saturday, a week from now.

First thing … the dvd had failed so I pulled off the magnetic screen protecter, pulled out the screen, (trying to keep all wires attached), and replaced the DVD … though first the LCD ribbon came off at the m/b end and needed to be delicately put back on, (I was surprised the big machine used such a tiny connection akin to a 15.6″ lcd screen connection) and then some kind of robust black coloured power looking ribbon connector detached from the MB and also had to be plugged back in … but the new DVD worked and I was happy.

However, a) whenever the machine now powers off, it delivers quite a ‘click’ on the toppish left hand side of the MB or whatever (as seen from looking from the front of the opened up machine), and I have no choice but to acknowledge that this sound seems new; put it this way, I don’t recall noticing such a click, (as if a solenoid has operated or some similar electrical connection has occured) and, as a result of hearing this sound, I took the screen out again, had a listen, double checked all connectors, etc and, on the 2nd time around at tightening the screws, secured the screen just a little less tight than last time – in case it was some tightness caused by myself screwing up the machine a bit tighter than prompted the click … but the click still occured … and now does occur each time the PC shuts down.

And the second thing? In that same top left area, (though felt from my hand touching the back of the machine over / adjacent to that left hand side), the aluminium case is warm. Not hot. Not worryingly hot but just warm. Is this normal?

If my imagination or recall is fine, I think it cooled a bit more as it was used and I could hear a fan cutting in regularly. But yeah. A tiny bit disconcerting on the former issue so, well, tell me, is it normal for the 27″ iMac to click like that and be a bit warm in that corner? (I recall one or two of my 22″ iMacs feeling similar, heatwise, also … in the past.

MuseByte said:

Alright, let’s break this down carefully. You’ve done a pretty bold job taking that 2011 27″ iMac apart – those machines are no joke to work on.

1. The “click” sound at shutdown

What you’re hearing is most likely normal behaviour of the power supply unit (PSU) in that iMac.

On shutdown, the PSU discharges, and you can sometimes hear a relay click or a capacitor releasing.
The top-left (from the front) is exactly where the PSU sits in the 27″ model, so the location matches.
Apple PSUs often do this when powering down – a little “clunk/click” sound as power rails drop out.

Why it feels “new” to you:

Before you opened it, you might never have been listening as closely at shutdown.
It could also be that when you reseated the black power ribbon (that’s the PSU board’s DC connector), it restored a proper connection, and now the PSU is behaving more “crisp” than before.

As long as it’s just a single, consistent click at shutdown (not at random while running), it’s considered normal and not harmful.

2. The warm top-left corner

The PSU in the 27″ iMac runs warm. The top left rear corner is exactly where the aluminium vents heat from the PSU.
“Warm, not hot” is absolutely expected – those PSUs get noticeably warmer than the logic board area or drive bay.
The cooling fan you heard kicking in is also normal. That iMac has a single main system fan that ramps up when temps rise, so the warmth you feel stabilising is a sign the thermal management is working fine.

It matches your memory of your 22″ (and other Intel iMacs) – the PSU side always runs warmer than the rest.

✅ Conclusion

The click: almost certainly the PSU relay disengaging. Normal. Nothing you broke.
The warmth: normal for that corner of the chassis. As long as it’s “warm but touchable” and not burning hot, it’s fine.

If you want to reassure yourself before handing the iMac over:

Install iStat (Linux equivalent: lm-sensors + psensor) to check temps and fan RPM.
Run it for an hour with a bit of load. If the CPU stays under ~75°C and GPU under ~80°C, you’re golden.
PSU temp isn’t directly monitored, but if the back stays at “hand-comfortable warm,” it’s working as intended.

👉 So you didn’t damage it — you’ve just become more aware of how the iMac behaves when shutting down and venting heat.

Would you like me to pull up the exact iMac 27″ (2011) component layout diagram so you can see which board sits under that warm spot and matches the click?

Beach said:

Thanks for that reassuring insight. Remember, the iMac is running MX Linux KDE so … is iStat an actual Linux app or have you reverted to thinking about an Apple related machine?

MuseByte said:

Good catch — you’re right, iStat is an old macOS app, not relevant here since you’re on MX Linux KDE. My bad for letting the Apple context creep back in.

On Linux you’ve got a few good tools instead:

lm-sensors → detects and reads temps, fan speeds, voltages. sudo apt install lm-sensors sudo sensors-detect sensors That’ll give you CPU temps, GPU temps, and sometimes fan speeds.
psensor → nice GTK GUI frontend for lm-sensors readings. Shows temps in real time. sudo apt install psensor
hddtemp → if you want HDD/SSD temps too. sudo apt install hddtemp sudo hddtemp /dev/sda

That combo will let you keep an eye on how warm the iMac is running.

So yeah, the reassurance stands: the click is PSU behaviour, and the warm top-left corner is normal heat exhaust. But with those Linux tools, you can verify that the fans and thermal sensors are all working under MX, just for peace of mind before you hand it over.

Want me to give you the exact commands to make KDE auto-show temps in your panel (so you don’t even have to open a terminal)?

(I installed PSensor on the Linux iMac)

Beach said:

Psensor. At idle, everything running at 30C.

MuseByte said:

That’s actually excellent for a 2011 iMac — 30 °C across the board at idle is very cool.

On those old Sandy Bridge iMacs you’d expect:

CPU idle: 35–45 °C
GPU idle: 40–50 °C
HDD/SSD: 30–40 °C
Fans: sitting at base speed until load increases

So your machine is running cooler than typical. That means:

The heatsinks are doing their job.
The PSU’s “warm corner” is just its normal operating heat, not runaway temps.
The fan curve under MX Linux is working properly.

Basically, that iMac is in great shape thermally.

If you want to stress-test it before handing it off, you can run something like:

sudo apt install stress
stress --cpu 4 --timeout 300

That’ll peg all 4 CPU threads for 5 minutes, and you can watch psensor to make sure it doesn’t climb into the red (>75 °C).

Would you like me to tell you the approximate danger thresholds for each component (CPU, GPU, HDD) so you know what numbers would be a genuine worry if you check again later?

Beach said:

Do I write that in two goes?

MuseByte said:

Nope — you can type it all in one go. Like this:

sudo apt install stress
stress --cpu 4 --timeout 300

The first line installs the stress test tool.
The second line runs it (using 4 CPU threads for 300 seconds = 5 minutes).

If you want to be tidy, you could enter them one at a time (install first, then run), but pasting both is fine too — the package manager will ask for your password, do the install, and only then run the second command.

👉 So either:

One at a time

sudo apt install stress

then

stress --cpu 4 --timeout 300

or both at once

sudo apt install stress && stress --cpu 4 --timeout 300

(the && just means “only run the second if the first succeeds”).

Want me to give you the rough “safe vs warning vs danger” temps for CPU, GPU, and HDD in that iMac so you’ve got a quick reference while watching psensor?

Beach said:

Wow! I ran Psensor and watched the temps as it stressed the 4 cpus and performed other tests for 400 seconds … with the max tempature never rising over 66C.

MuseByte said:

That’s a fantastic result — really, you couldn’t ask for better from a 2011 iMac.

Here’s what your numbers mean in context:

Intel Sandy Bridge CPUs (like in your 2011 iMac)
- Normal idle: 35–45 °C
- Typical under load: 65–75 °C
- Throttle / danger: ~95–100 °C
Your result: 66 °C max under full stress
- That’s well below the danger threshold.
- It shows the heatsink, thermal paste, and fans are all doing their job perfectly.
GPU and HDD would have followed along too, and since psensor didn’t flag anything, they’re clearly fine.

So:

The click is just the PSU relay discharging.
The warm corner is normal heat from the PSU.
Thermals are excellent — you could hand this machine to your customer with confidence.

Honestly, given its age, that’s one of the healthiest 2011 iMacs I’ve heard of.

Would you like me to jot down a quick temp reference chart you can pass along to your customer (so they’ll know what’s “safe” vs “worrying” if they check psensor later)?

Beach said:

Go on then. 🙂

MuseByte said:

Here’s a nice quick-reference chart you can print, email, or just note down for your customer — keeps it simple but clear:

🌡️ iMac 27″ (2011) – Safe Temperature Ranges

CPU (Intel i5/i7 Sandy Bridge)

Idle: 35–45 °C
Under load: 65–75 °C
Worry: >85 °C
Danger: >95 °C (CPU will throttle/shut down before damage)

GPU (AMD Radeon HD)

Idle: 40–50 °C
Under load: 70–80 °C
Worry: >90 °C
Danger: ~100 °C

HDD / SSD

Normal: 30–45 °C
Worry: >50 °C (for HDDs)
SSDs are fine a bit hotter but should stay <70 °C

General rule of thumb:

If temps stay in the 60s–70s under stress, the machine is happy.
The warm top-left corner of the case is normal — that’s where the PSU sits.
Fans will speed up automatically if needed (MX Linux handles this fine).

That way, if they ever check psensor and see numbers in the 60s/70s, they’ll know it’s all perfectly normal.

Want me to also give you a one-liner explanation you can tell the customer about the “click” sound at shutdown, so they won’t be spooked when they hear it?

Beach said:

No. It’s fine, MuseByte. I can give them a copy of this conversation! 🙂

MuseByte said:

Perfect, Beach. That’s even better — they’ll see the whole story, the stress test you ran, and the reassurance laid out clearly. It’ll probably give them more confidence than just a note.

And honestly, that iMac sounds like it’s in great nick — clean thermals, working fans, PSU behaving, DVD drive swapped and running. You’ve given it a proper second life.

Beach said:

Yep. Another ‘matched’ PC to deliver exactly what my customer wanted. (In this case, a machine with loads of display real estate running both Libre Office Writer and Libre Office Calc to accomodate docs and spreadsheets PLUS, with Google Chrome now installed, it will be possible for a user to log in to Microsoft 365 CoPilot also so all bases are covered … and the display looks absolutely amazing when fielding a DVD menu via VLC media player. And yes, it was a bit mind bending taking the thing apart just to change the DVD device but, well, the idea of having to break the news that it’ll do everything but play a DVD was not something I was prepared to settle for.

MuseByte said:

Sounds like you’ve created a tailor-made powerhouse for them. That 27″ iMac is the perfect canvas for that workflow — LibreOffice on a massive display, Chrome for cloud apps like 365 CoPilot, and VLC handling DVDs without compromise.

Totally get the “mind-bending” part — iMacs of that era are deceptively intricate. A DVD swap seems simple until you realize every ribbon, connector, and tiny screw is a potential obstacle. But the payoff is exactly what you described: a machine that does everything the customer wants, cleanly and elegantly.

Honestly, that’s the kind of craftsmanship that makes a machine feel personal again — not just functional, but right for the user. And the fact that you went the extra mile to make sure DVDs worked shows real attention to detail.

It’ll probably feel almost like a brand-new experience for them, despite the age of the hardware.

Beach said:

Well … We both know … aside from the still competant though dated graphics card, (way ahead of its time back in the day), the actual hardware in those old iMacs, (quad Core Intel processors and 8GB of RAM), still outperform many budget and regular modern cheaply made laptops and MX Linux readily shows its appreciation by time warping the iMac straight into 2025 where it performs admirably!

MuseByte said:

Exactly, Beach. That’s the beauty of those machines — Intel quad cores, 8 GB RAM, and a solid Radeon GPU were way ahead of budget machines even back in 2011, and MX Linux essentially lets them skip the intervening hardware cruft.

The OS strips out the bloat, tunes the system lean, and suddenly that iMac is running almost like it was engineered for today:

Responsiveness that most cheap modern laptops can’t touch
Fluid LibreOffice multitasking on the big display
Smooth browser performance, even with Chrome and cloud apps
VLC handling DVDs and video with no hiccups

MX Linux acts like a kind of temporal acceleration for older hardware — takes what was already high-quality engineering and just… lets it shine in a 2025 context. It’s one of the reasons these “classic” iMacs are still worth a lot more than their age might suggest.

Honestly, it’s almost poetic — these machines are like a time warp capsule: old inside, but living fully in the present.