[R-390] More On Low Audio Problem

Cecil Acuff chacuff at cableone.net
Sat Dec 17 12:53:58 EST 2005


Fred,

    In the wide position the response switch S-104 should be already 
shorting pin 1 to pin 6.  If you are using a clip lead to connect pins 1 and 
6 and it restores audio you have a bad contact on S-104 or a broken wire 
between pins 3 and 9.

Looks like you are close...

I didn't have a schematic for the 390A from the shop but used the pull out 
in the TM11-4000 that was already on my desk here in the house.  I hope the 
designations are correct...I believe the schmatic to be.

Cecil....
----- Original Message ----- 
From: "Frederick Bray" <fwbray at mminternet.com>
To: <r-390 at mailman.qth.net>
Sent: Saturday, December 17, 2005 11:40 AM
Subject: [R-390] More On Low Audio Problem


> First, let me thank everyone who has replied -- both on and off list.
>
> I think I have narrowed the problem down to the first AF amp/cathode 
> follower.  I would appreciate it if those who are more experienced that I 
> with the 390A can confirm that I am on the right track.
>
> I used an audio signal generator to ascertain that a signal injected at 
> the local and line level controls seems to produce a normal audio output.
>
> Using a VTVM, I confirmed that on there is an AC voltage on terminal 1 of 
> the wide/sharp switch and that I can trace this voltage through the 
> switch.  Jumpering this voltage to terminal 6 on the switch seems to 
> restore the audio level to approximately normal, or at least much closer 
> to normal.
>
> From looking at the schematic, I think that what I am doing is bypassing 
> the first AF/cathode follower and going directly to the local and line AF 
> amps.
>
> Does this make sense?
>
> Thanks,
>
> Fred Bray
> KE6CD
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