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Downed TV channels could soon return; WGBH will briefly be off the air

Public television station WGBH will briefly stop broadcasting over the air on Tuesday afternoon, in a bid to restore service at three other local TV stations that have been down since Sunday night.

Over-the-air broadcasts from CBS Corp. stations WBZ-TV Channel 4 and WSBK-TV Channel 38, ABC network affiliate WCVB-TV Channel 5, and PBS station WGBX-TV Channel 44 shut down at about 8 p.m. Sunday. All four stations share the same antenna, located atop a 1,200-foot tower in Needham.

WCVB-TV quickly resumed broadcasting through a backup antenna, but the other three stations have stayed off the air. The outage has had no effect on the great majority of viewers, because the stations continue to feed their signals to cable and satellite TV providers, who serve about 98 percent of viewers in the Boston area.

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Paul Pabis, director of broadcast operations and engineering for WBZ and WSBK, said the outage is apparently due to a breakdown in a “five-way power divider,’’ an electronic component that separates the signals from multiple stations before feeding them to the antenna. Fixing the problem will require a complete shutdown of the antenna. But it’s a two-stage antenna, and part of it is still being used to broadcast PBS station WGBH.

Engineers for the affected stations think they’ve found a solution. They plan to briefly shut down WGBH at 1 p.m. Tuesday, then move its signal to the backup antenna being used by WCVB. Then WCVB, WSBK, WBZ, and WGBX will all begin broadcasting from the WGBH antenna.

“In theory, it’s a good plan,’’ said Pabis, and will get all the stations back on air quickly.

Next, each station will install a temporary antenna on the tower. After that, the WGBH antenna will be completely shut down. The power divider can then be repaired.

Pabis praised his fellow TV station engineers, saying they’ve worked together closely to get everybody back on the air as soon as possible.

“We’re a fairly closely knit group so we work together,’’ Pabis said.

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