CAPE CANAVERAL - A faulty electronics box will be replaced on one of shuttle Discovery's solid rocket boosters, but the work won't delay NASA plans to launch its second post-Columbia flight July 1.

Technicians will do the job at Kennedy Space Center's Launch Complex 39B. NASA has more than a week of extra time in the processing schedule leading up to the opening of a window that extends through July 19.

"We're taking weekends off. That's how well the flow is going at the pad," said Kyle Herring, a spokesman for NASA's Johnson Space Center in Houston.

During routine testing last week, engineers testing the booster's power distribution system noted an unexpected power shift from a prime to a backup circuit. It wasn't clear what prompted the shift.

NASA engineers now think the culprit is a faulty integrated electronics unit, a device that serves as the primary communications link between the booster and shuttle orbiter computers.

Each booster is equipped with two of the electronics boxes. They provide control electronics for the booster during launch, ascent and separation as well as booster splashdown and recovery.

The faulty unit will be replaced in the coming weeks while other prelaunch work continues.

Technicians have swapped the electronics boxes during at least two previous launch campaigns.

An STS-43 launch attempt in 1991 was delayed a day to replace one of the units.

The boxes on both boosters were replaced at the pad prior to the STS-96 launch in 1999.

• NASA Clears Foam Debris Issue for Next Shuttle Flight
• STS-121 at the Pad: NASA's Discovery Shuttle Reaches Launch Site
• STS-121 Astronauts Train Hard for Shuttle Launch
• Shuttle Discovery Moves Closer Towards July Launch
• NASA Forgoes Fuel Tank Test for Next Shuttle Launch
• Return to Flight: NASA's Road to STS-121

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