[NLRS] HP 431B question

[Charlie Betz]

I hope someone on the reflector has experience with this power meter and 
can answer a question.

I was given an HP431B power meter and 478A head for evaluation to see if 
I was interested in buying it.  The head is supposed to be good.

I plugged the 478A head into the power meter and powered the meter up.  
I have nothing connected to the N connector on the power head, i.e. the 
input is open.  As such, the meter pegs full scale on every position of 
the range switch other than the NULL position.    If I unplug the head 
from the cable the meter reads zero on all positions of the range 
switch.  What I am wondering is whether or not  this is indicitive of a 
blown power head?  I suspect it is, but I really have no experience with 
one of these meters, so I really don't know.

Charlie, N0AKC