[Jeffhs]

It seems to me the brightener could be defective (may have been for years, if it has been on the tube since the 1970s). Removing the brightener must have removed the short or whatever it was which was killing your vertical sweep if you now have a picture again, although if you lost both sweeps at once (but still had HV, which of course means the horizontal sweep must still be working) with the brightener in the circuit, that would seem to indicate the brightener itself is indeed defective.

Your TV also, obviously, has a weak CRT, if the set has had a brightener on the tube for who knows how long. However, before replacing the CRT (I don't know if 27" CRTs are still made today), I would try replacing the brightener since, as I mentioned, it may have an internal short which is killing the vertical sweep. If both sweeps work with the brightener out of circuit, that seems very likely.

Of course, if you are getting only a bright dot in the center of the screen, turn the TV off immediately, and keep it off until you find and correct the problem. Otherwise, the dot will burn itself into the phosphors in the center of the tube, similar to "ion burns" CRTs used to get years ago when the vertical sweep quits. Once this happens, of course, the tube will be ruined forever, as there is no way to repair or undo the damage vertical sweep failure will cause.