50x 34401a ?? wow
it depends on the serial numbers, old one ... have the non available vfd driver ic .... unless you put a cloned vfd, you wont be sure if it is the ic of the vfd itself
and more recent, have other vfd driver chip that can be found or subbed, and too this cloned vfd can be found ... prices have gone up
you must be very careful if you remove the lcd and put a new one, legs can be much longer and may kick on the front panel and you may damage it while sliding it into place
and yes check all voltages going on the vfd / front pcb
and one more advise, you can not switch old vfd driver board into the more recent one, and the other way, the display firmware is not the same
if i recall < 7 display fw is the old vfd ic and >7 is the newer ... others members may chime in
you have to find Keysight notes about the SN ...