Four Greater Boston TV stations are racing to repair a mysterious malfunction that knocked them off the air on Sunday night.
The affected stations are CBS affiliates WBZ-TV Channel 4 and WSBK-TV Channel 38; ABC affiliate WCVB-TV Channel 5; and PBS station WGBX-TV Channel 44. Over-the-air broadcast signals for all four stations were cut off at about 8 p.m. Sunday, due to an electronic fault that still hadn’t been diagnosed as of Monday afternoon.
“We have crews on the tower at the moment trying to isolate exactly where the problem is and repair it,” said Paul Pabis, director of broadcast operations and engineering for WBZ and WSBK.
Most TV viewers aren’t missing anything. The stations continue to transmit over cable TV and satellite services, which are used by about 98 percent of viewers in the Greater Boston area, according to data from the Television Bureau of Advertising. Pabis estimated that 93 percent of WBZ’s viewers use such pay-TV services and have not been affected by the outage.
While WBZ, WSBK, and WGBX are still off the air, WCVB has resumed broadcasting at lower power through an auxiliary antenna.
Pabis said the the four affected stations share the same antenna and transmission line. He said that a transmission line failure is the most probable cause of the problem. “Transmission line failure is pretty common,” he said. “Copper lines tend to burn out pretty often.”
But Pabis added, “I can’t remember the last time it happened to us.”
The line in question is a rigid, copper-sheathed coaxial cable that runs up the 1,200-foot-tall tower in Needham which hosts the antenna. A second line is in place, but must be connected to the antenna by workers who make the long climb up the tower. Pabis said that on their first trip up the tower — about a half-hour climb — repair workers discovered that they didn’t have the correct part to connect the auxiliary line to the antenna. “They had to come all the way back down, get that piece, and bring it up,” Pabis said.
Pabis said it’s unlikely that the antenna itself is malfunctioning. But if it is, repairs will take much longer, because an antenna must be custom-made to transmit the signals from all four stations. “That would take quite some time,” he said.
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