MILPITAS, Calif. -- There may be a ticking time-bomb in millions of Pentium motherboards. The problem boards--often low-cost or no-name brands--skimp on the number and quality of capacitors that are required to smooth out voltage spikes around the CPU, a U.S. electronics executive has charged. As a result, they don't meet Intel's power specifications and are subject to unexpected failures that could trash data and files of unsuspecting consumers.

"Your processor locking up may not be [caused by] your software--it could be cheap power-supply components on your motherboard," said the executive, Bob Dobkin, a vice president at Linear Technology Corp. (Milpitas, Calif.). "This is potentially a bigger problem than the Intel Pentium floating-point bug because there are millions of computers that could go bad."

The root of the problem is that it's far tougher to design a board with Pentium and higher CPUs than it was to use the earlier-generation 286, 386 and 486 chips. The reason is the more-stringent voltage and current requirements of today's 32-bit CPUs.

The problem only gets worse with new MMX-technology chips like Pentium II (code-named Klamath), which will be formally unveiled on May 7. Pentium II, for example, requires voltages that vary from 2.1 to 3.5 V, and currents that can go from 300 mA to 8, 10 or 12 A, and back again in a single clock cycle.

Dobkin is hardly a disinterested observer -- his company makes motherboard voltage-regulator ICs -- but his views were echoed by other industry sources.

"This is very true, especially with Klamath," said Larry Barber, president of motherboard maker Tyan Computer Corp. (Milpitas, Calif.). "Klamath has an extremely strong surge when it kicks in."

"What we have found is [that] there is a cutting down on the number of caps--the amount of decoupling that's used," said Yogesh Mittal, an engineer at American Megatrends Inc. Some 40 to 50 decoupling capacitors are required for a Pentium Pro CPU alone, he said.

"With higher CPU clock frequencies, boards are more susceptible to spikes," said Shanker Munshani, president and chief executive of Micronics Computers Inc. (Fremont, Calif.). "But high-quality tantalum capacitors cost 11 cents to 29 cents. If you use several hundred caps on a board for decoupling, it adds up pretty quickly."

As a result, some board makers skimp and use electrolytic capacitors instead of tantalums. High-quality electrolytics, such as those made by Sanyo-Oscon, are available. However, some cost-cutting vendors use cheap electrolytics that cost only a couple of cents each, Munshani said.

According to Dobkin, in a test of seven randomly chosen boards, five were out of spec. For example, a Soyo Computer Inc. model Triton/P54C PCI Mainboard exceeded the 3.4-to-3.6 V CPU supply-voltage range (3.5-V nominal) by approximately 50 percent. (Soyo's U.S. office didn't return calls seeking comment. The parent company, in Taiwan, could not be reached at press time.)

The Soyo board had 11 capacitors. A $99.99 board from EFA, which was another poor performer in Dobkin's test, had 21 capacitors. In contrast, a Tyan Computer motherboard, which passed with flying colors, had 54 on-board caps.

"The problem with low-cost electrolytic caps is they age," said Dobkin. "And when they age, their ESR [effective series resistance] drops. These caps are sitting close to the processor, where they get heat, which makes it worse.

"What happens is, you run your PC for a year or two, these caps dry out, and all of a sudden your PC locks up," Dobkin continued. "On a power-cycle transient, the voltage gets outside of the range for the processor to operate properly and you flip some bits inside and the microprocessor will lock up. It will often look like a software failure, but it's not."

Indeed, the lowly capacitor has a big impact on how well a board works. "It all depends on how long you want your motherboard to last," said Chris Kelly, a components engineer at Intel's operations in Hillsboro, Ore. "Heat is the biggest problem -- it drys out your capacitors. The actual electrolytes will start to dry out. This reduces the ESR. And if the ESR drops, the overall heat that has to be dissipated by the field-effect transistors driving the processor has to increase. So it's a cascade function."

The solution, Kelly said, is to "use more caps, in parallel, on the board so that the ESR you start out with is much more than you need, so that three years down the road you're still OK."

One way for OEMs to check that boards are within spec is with an Intel power validator, a piece of hardware that sells for approximately $1,000.

For its part, Intel "overspecs and overcaps its designs" to avoid any potential problems, he said.

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