[R-390] new member, R390A, no signal when first powered on, works after 10min but RF cutting in and out

[weekspat at imonmail.com]

Hi,

I got a Motorola R390A, signal corps unit last year.  Have recapped,
and fixed most problems, but I've got one nasty intermittent one.
 Seems like the RF signal is not getting to the RF AMP and or
conveter or thru it, so I think I've got no signal to the IF section.
 Then after some time it starts making some popping sounds and
shortly after that "pops" on with normal reception.  Happens on all
bands.  I'm wondering if those mini BNCs are to blame.  Any hints ?
 The problem sort of " comes and goes" so its hard to nail down
thanks, Pat Weeks