A blown capacitor on a control board caused Tuesday morning's power outage for 4,000 customers in parts of Whitehorse and areas to the north, says Yukon Energy spokeswoman Janet Patterson.

Staff found the problem and replaced the card on the number four turbine at the Whitehorse Rapids Dam, she said today.

The turbine, the largest on the Whitehorse-Aishihik-Faro grid, was off-line for almost eight hours until the problem could be isolated and repairs made.

Power went out at 8:25 a.m. but all customers were back on in 20 minutes or fewer, and the fourth turbine was back on line at 4:05 p.m.

Once the problem was identified, it didn't take staff long to replace the card, she said.

Three diesel generators were fired up to fill the void, two of which were shut down shortly after 12 p.m. The third was taken off-line shortly after 3 p.m.

The card is used on a component called the exciter, which converts the turbine's spinning energy to electrical energy.

Electricity was knocked out to Riverdale, Porter Creek, subdivisions along the North Klondike Highway and a portion of Faro.

Tuesday's outage was the third in less than a week.