--A Fantastic Tale of Solving the Unsolvable--
Some years ago, a friend decided to buy his first personal computer in the World Wide Web era (he had been and continues to be an avid WebTV user). Due in part to my encouragement, he chose to buy a Macintosh. Careful shopping resulted in the purchase of a year-old iMac 333MHz. I accompanied him on the trip to purchase the iMac from a private individual - I performed some rudimentary tests upon the hardware and affirmed the used iMac's fitness.
If I hadn't witnessed this myself, I wouldn't have believed it. This is a computer diagnostician's horror story.
Not long afterward, the friend reported a problem: the cursor would intermittently freeze. Curiously, he discovered that in an unpredictable period of time (from minutes to hours), user control sometimes eventually returned. The symptoms appeared while he was running a variety of applications. The circumstances under which they appeared had no apparent commonality.
My friend's comment about this previous paragraph: "This caused incredible frustration with the iMac, even causing me to put it away and not touch it for about 3 months when I first tried to learn how to use it. It was my first Mac and after experience with bullet-proof DOS machines, a real disappointment until the problem was discovered."Some known issues of the time exacerbated our inability to solve his problem. For instance, Apple had identified a problem with slot-loading CD drives which caused system freezing and had released a firmware upgrade for the CD drive. This produced no helpful results.
Many diagnostic experiments were performed attempting to solve this problem:
- keyboard & mouse replacement
- RAM replacement
- formatted drive
- installed OS 8.5, 8.6, 9.1, 10.2
- firmware update per Apple
A couple of years passed, and this was always nagging at me: the problem I never solved; the friend's Mac that I couldn't fix; the friend's Mac I'd convinced him to buy and approved for his purchase.
Eventually, after formatting the iMac's internal drive and installing OS 10.2, the symptoms persisted. I gave up, assuming that the problem was hardware-related. Perhaps it was USB-circuit related - a motherboard swap as the likely fix.
Instead of replacing the motherboard (a decidedly unprofitable move, in the face of the changing state-of-the-art - and what would have been a disastrously unsuccessful move, given the final outcome), he decided to buy a new computer. I suggested an eMac. After some deliberation, he bought a brand-new eMac 700MHz.
Two weeks later, my phone rang.
Friend: "You'll never guess what's happening with my new eMac."We apparently didn't resolve the problem in that call. A few days later, when the friend experienced the problem again, he experimentally removed the surge suppressor from his computer, plugging directly into the wall outlet. He experienced NO further problems.
Me: "No way."
Me: "Are you using the new keyboard and mouse?"
Friend: "I'm using the keyboard and mouse that came with the new eMac."
Not only did he never see the problem again, but he fired up the old iMac and never saw the problem there again either. Re-installing the surge suppressor re-introduced the Temporary Frozen Cursor symptom. After running both machines for weeks with no symptoms, his conscience was clear enough that the iMac was completely fine that he eventually sold it for not much less than he purchased it two or three years earlier.
(NOTE: Surge suppressor model: “Surge2+”, model 30022, UL listed, bought at a Home Depot for about $10, with “$5000 equipment damage guarantee.” I don't recommend it.)If he hadn't purchased another brand-new computer which was identically vulnerable to whatever characteristic was introduced by the surge suppressor, we'd never have had a solution. I've told this tale within my circle of technically-adept friends, and not one of them would ever have suspected this possibility.
Having said that, I hope never to suspect a surge suppressor again. It's just too strange. I can't believe it's even possible. In all my years as a computer hobbyist and professional (since 1981), I've never seen anything like this. Especially that whatever the mechanism of failure was, it caused a 1999 iMac and a 2002 eMac (which probably have completely unrelated power-supply circuits) to temporarily stop responding to the USB bus, only to completely return to normal functionality in time - without crashing the computer.
I've posted this, not with the expectation that it will actually be the solution to anyone's symptoms (but by all means let me know if you encounter this), but because this was also a painful learning experience. I had been thorough in my diagnostics of his iMac. None of the hardware or software infrastructure which I was able to test on his computer were at fault. But my mind was closed to the possibility that something _past the plug on the AC power cord_ could be suspect. When you're a diagnostician, you tend to adopt a process of elimination. Mistakenly eliminating a part of a system without can lead down a an inappropriate logic path - and I know that. I will frequently review the eliminations I've already made, to check for careless logic errors. And yet, I never even included the AC power source in my mental logic tree.