The "zipper" has been "down" a few times in its history.
3 January 1981, New York (NY) Times, pg. R2:
He said the revolving news or "zipper" sign will be reinstated, and that its annual operating cost of over $300,000 will be shared by several companies.
28 December 1982, New York (NY) Times, pg. B3:
The "zipper sign," which started flashing news messages in 1920, is to run the New Year's Eve countdown and then return to full serice in February.
11 December 1994, New York (NY) Times, pg. 60:
The zipper is the moving illuminated bulletin board that began carrying headlines around the triangular building at 42d Street and Broadway on Nov. 6, 1928.
The New York Times...sent headlines flashing around the tower between 1928 and 1963. (...) After The Times stopped operating the zipper, it went dark for 27 months. (...) The zipper went dark again between 1977 and 1986,
30 December 1994, New York (NY) Times, pg. B3:
Times Sq. Flash: ***ZIPPER SAVED***
Back in the early 50’s, I was with a group of Boy Scouts who had a tour of the office that contained the “control center” for the “Zipper” sign.
No electronics in those days, it was all mechanical. A long, conveyor machine with hundreds of metal fingers sticking up through a long, horizontal track. The conveyor passed 5x7” sheets of bakelite (before plastics) with metal letters attached to each, over the metal fingers. Each finger was directly wired to a bulb on the zipper sign outside, forming a letter in lights that circled the building
as the metal letter moved along the fingers inside.
Did anyone else see that machine? Let’s talk.