WHEN the air-conditioning went out one day last summer, Norm Bailey's computer shut down mysteriously.
Panicked, he and his colleagues at a General Dynamics lab opened up the computer case. Their finding: The machine's main chip, a 486-class microprocessor, had overheated.
As sales of 486-class computers go through the roof, a few computer users and vendors are raising new concerns that the chips run too hot. In some cases, computers have overheated, shutting down temporarily or, in extreme cases, corrupting data or the magnetic disks that store it.
Such occurrences appear rare. Intel Corporation, which makes the 486 chips, says it has had no complaints about overheating. But with summer just around the corner, some users and vendors are urging caution.
"Our customers want a reliable machine," says Jeff Alessi, chief engineer of Compu-Electronics. "Any integrated circuit that runs cooler is going to last longer." So the company, a small assembler of personal computers in Lincoln-wood, Ill., puts a device to diffuse heat on each one of its 486 systems running at 50 megahertz (MHz).
"I believe you're going to have a severe problem," says Mr. Bailey, president of PCubid Computer Technology in Sacramento, Calif. " `Severe' might be just 1 percent of the population, but how would you like to be Hartford Insurance running a `mission critical' application and something happens?" Overheated chips
The faster the chips run, the hotter they get. Intel's fastest 486 chips - the 33 MHz, 50 MHz, and a new variant called a DX2 - run close to their maximum operating speed. How close is hard to say. Intel pegs the official operating limit at right around 185 degrees Fahrenheit.
Lew Pacely, Intel's product-line manager for 486 chips, says the chips sometimes run higher than that - up to an estimated 194 degrees. But, he adds, Intel has built a margin of safety into its official limit. (Mr. Pacely will not say what that margin is.)
"It's definitely a solvable problem," he says, as long as computer companies build in devices that adequately cool down the chips. "I've heard absolutely zero" about the overheating problem, he says.
Apparently Pacely has never talked to Dan Daniels.
"The 50 MHz? It'll usually die within 30 minutes" without a cooling device, says Mr. Daniels, director of operations for Bay Engineering Company. The Coos Bay, Ore., company had several 50-MHz 486 workstations fail last December. Now it includes a heat sink on every 50-MHz 486 it sells.
The most popular way to cool personal computers is to install a fan - or even two fans. Computer experts suggest consumers ensure that fans are aimed at the processor and that the computer case is not tightly packed.
After his 486 computer overheated last year, Bailey, a General Dynamics engineer, built his own solution. It is a heat sink - a small finned contraption that cools the processor by conducting and dispersing its heat. Heat sink becomes popular
The solution proved so popular among colleagues that Bailey left his job last month to sell his gadget full time. His Sacramento, Calif., company has heard from more than 500 people with overheated 486 computers.
One of them is Woon Low, manager of Proven Technology, a small personal-computer vendor in Sacramento, Calif. Five of his 486-class computers overheated and stopped working. The conditions were extreme: the computer ran networks round-the-clock next to big disk drives (which generate even more heat than 486 chips.)
So two months ago, he installed Bailey's PCubid heat sinks. The file servers have not overheated since.
In its Jan. 20 issue, InfoWorld reported that several 50-MHz 486 machines it tested overheated. The industry publication concluded the machines used the first run of Intel chips, which the company recalled last summer. These first-run chips should no longer be on the market.
Some manufacturers have solved the overheating problem, Bailey says. Hewlett-Packard Company includes its own heat sink, for example. Others, such as Gateway 2000 Inc., have not, Bailey adds. Still others have not seen any problems but are playing it safe anyway. Craig Dwayne of PC Pros/Touche in Darien, Ill., installs a heat sink in every 50-MHz 486 he sells. "For $20, it's just not worth having those frustrations," he says.