This has been well documented on other sites, such as AVS Forums and fybush.com.
Basically the transmitting upper master antenna for channels 4,5, 38 and 44 digital had a piece of RF equipment became damaged Easter night forcing the stations off the air. Channel 2, which uses the lower master antenna was not affected. (Both are broadband master antennas. The lower antenna handled the analog signals of 38 and 44, along with digital 2 (RF 19).)
About 500 feet up the tower, a very small low powered backup antenna existed for WCVB RF 20. A couple of days later, WGBH relinquished their master antenna for the combined signal to be moved to the lower master antenna. WGBH's signal was then moved to the WCVB standby antenna. Two weeks later, two new UHF smaller master standby antennas were temporarily hung on the upper mast to keep the stations on the air. The top mount antenna had to be removed (from 1300 feet in the air, mind you) and brought down to be shipped back to the Dielectric factory in Maine for repair. The antenna is currently been removed, and should be replaced in about two months.
Channels 7, 25, 56, 62, 68 are not affected and all operate from other towers in the same general area.