Note: This was originally posted on our Nectarine OZ site, but as it seems to have saved quite a few people from geek trauma, I figured it was worth re-posting here...
A couple of days ago I noticed Bek's gorgeous 24" iMac screen was suddenly looking fuzzy. Some of it seemed sharper than other bits, but some areas were definitely soft and slightly out of focus. Uh oh...
A bit of googling suggested it could be font-smoothing settings, but playing with that had little effect- except that I did notice that when I moved the cursor over the smoothing drop-down menu, the whole screen would shift a pixel or so to the left! Roll off, and it popped to the right.
I felt my heart stop for a couple of seconds. Not some horrific motherboard or video card failure, surely? We'd bought the iMac second hand at a great price from someone who was heading to a MacBook. I zipped off to Apple's warranty check, and sure enough, we've just moved out of the coverage period. Ah well, you takes your chances and you rolls the dice...
More googling suggested that resetting the SMU (System Management Unit- sometimes labeled the SMC or System Management Controller). It's a microcontroller chip on the logic board that controls all power functions, and is sometimes implicated in video/fan/sleep issues.
Well, that was a saga of trawling Apple's arcane Mac labelling system (is your iMac an early/mid/late model, or the 'ambient light' model, or...?) and cross-referencing that against the SMU resetting methods: remove all cables including power, wait a minute, replace power while holding down the start button- unless you've got the revised model, and then you don't hold down the start button- oh, wait, you've got that iMac, no it's different again!
Suffice to say, none of it made any difference.
With a heavy heart, I came close to calling a Mac store to book it in. Then I thought "No! I'm not done!"
Something had twigged in my mind: that single pixel shift when over the font smoothing menu. I moved the cursor to where that menu had been on screen- and it happened even without the menu there! Something swam out of the depths of my random Mac arcana- screen zooming.
And sure enough, a quick trip to System Preferences/Universal Access/Seeing showed that screen zooming was on. Turned it off and Shazam! - crystal sharp screen display again!
Somehow Bek had activated zooming- probably an accidental hot-key activation, as she's Queen of The Hot Keys in Flash/Photoshop/Illustrator et al. The zoom level must have been something like 101%- just enough that the interpolation lead to areas of fuzziness. And exactly enough zooming to mean that when you crossed the centre line of the screen, it panned to show the single pixel of lost screen real-estate! (Didn't happen if you moved the cursor vertically across the centre- the zoom that way must have been less than a pixel, and only the extra size of the horizontal dimension pushed it to a full pixel and panning).
So it's back to 24" nirvana, and a regular heartbeat again. Hopefully, this post can save someone else from Mac screen trauma too!