May 1, 2008 5:20 PM PDT

Report: Fastest AMD chips run with circuit-board fix

Posted by Brooke Crothers

Inexpensive circuit boards can work reliably with the fastest AMD quad-core Phenom processors when modifications are made, according to a report. This comes in the wake of mismatch issues between Phenom chips and select motherboards, as reported by Asia-based vendors.

Gigabyte AMD 780G-based motherboard

(Credit: Gigabyte)

The mismatch between high-end Phenom processors and lower-end motherboards became an issue when some Asia-based manufacturers attempted to plug in 9750 and 9850 Phenom processors into boards based on AMD's 780G chipset. The chipset is attractive to board makers because of its relatively high-performance integrated graphics. (A motherboard is the main circuit board in a PC.)

On Monday, AMD spokesman Jake Whitman said this to CNET's nanotech: the circuit's blog: "What people have done, mistakenly, is paired a 780G (chipset-based) motherboard with the higher frequency Phenom--the 125-watt Phenom."

AMD recommends using a higher-end 790 chipset-based motherboard.

Because of the higher thermal envelope of 125-watt Phenom chips, heat can cause stability issues on less-expensive motherboards, according to a report at tech Web site AnandTech. One of the problems is that some of the less-expensive boards claim support for 125-watt chips.

Against this backdrop, AnandTech demonstrated that motherboards with the 780G chipset will work reliably--with some modifications.

Boards were tested from Gigabyte, Jetway (PDF), ASRock, and Biostar. The tested boards from all four companies support the 125W processors.

"Each and every manufacturer, along with AMD, agreed that cooling the MOSFETS properly was critical to the successful operation of the board at stock or overclocked speeds with the 9850BE--and to some degree, the 6400+ X2," AnandTech said.

(A MOSFET, or metal-oxide-semiconductor field-effect transistor, handles voltage regulation on the motherboard.)

"This is based on the board manufacturer utilizing a properly developed power delivery system that is designed to handle the 125W TDP processors and in the future, the upcoming 140W TDP Phenoms."

AnandTech said it got around the problem by installing a second fan or a modified heatsink. "We installed a secondary 120mm fan that provided enough airflow over the board to ensure stable operation under our load scenarios."

Originally posted at Nanotech: The Circuits Blog

Brooke Crothers is a former editor at large at CNET News.com, and has been an editor for the Asian weekly Wall Street Journal and an analyst at IDC. He writes for the CNET Blog Network, and is not a current employee of CNET. Contact him at brooke_crothers@msn.com. Disclosure.