[R-390] question

[Tim Shoppa]

Saying the stage involved is easy in this case: there's a tunable IF
(including switch contacts, mixer, 17Mc osc, and more switch
contacts) that exists below 8Mc but not above 8Mc. This tunable
IF is in the middle rear of the RF deck with the 17Mc osc
can in the extreme right rear.

If it "goes completely out and then comes back on" can
be split up at least 4 ways:

  If it "comes back on" below 8Mc as a result of twiddling the MC knob,
  it's probably switch contacts deep in the RF deck and might
  be fixed by cleaning these up, or (more likely) realigning
  the bandswitch mechanism.

  If it "comes back on" below 8Mc after a while with no knob
  twiddling, maybe the 17Mc osc has a hard time starting.

  If it "comes back on" below 8Mc as a result of AGC recovery
  time, then you might have drastically low sensitivity below
  8Mc, which might be a misaligned IF section or even the
  IF slugs not moving in and out or just a crappy tube or
  something under the IF deck. (I've also seen some funky
  self-oscillations in some IF stages that can seriously whack
  out auto AGC while being completely inaudible to the ear).

  If it only "comes back on" by tuning Mc knob at or above 8Mc,
  then it's not an intermittent but solidly down, and could be
  anywhere in that IF stage or its switches.

There are test points on the top of the RF deck and you
can also check the 17Mc osc with a loop of wire hooked to
a scope, placed around the vicinity of the 17Mc osc.

Tim.

>>> <radio52 at sbcglobal.net> 6/27/2007 11:19 PM >>>
I'm new to this list. I have a Collins R-390A that receives
very well from 8Mhz on up... but from 7Mhz on down the
receive goes completly out and then comes back on. Anyone
have some clues where I should start to look on solving
this problem? I am not to tech savy 

Thanks 
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