[Milsurplus] Align Mil radios if/filter -HP 8601A sweeper - output meter does not Zero

[John Hutchins]

Group -
8601A - output meter does not Zero

I have acquired 4 8601A 3 for parts. Attempting to get one to work with 
in spec.  I need this unit to align restored Mil-SW receivers with 
crystal filters.
I know nothing about operating the equipment at the moment.  Initial 
testing in CW mode shows on all, the output meter does not Zero.
Any Ideas on where to start?
Source for a OPS/service manual?

Thanks
Hutch