AVCOM PSA-65C poor sensitivity

[FO4MM]

Hi to all,

First, I'm not an RF geek but i think that i have an idea of what could be wrong with this S.A.
Even connecting an exterior discone into its RF input , the FM commercial spectrum is very weak (knowing that a scanner or another S.A. is giving good signals with the discone)
I would suspect a problem into the front end of this test instrument (although it works, but....)

Anybody have has similar experience with this avcom ?

Thank you

By the way : it is a real pain to find its manual on the net !!!