[R-390] More On Low Audio Problem

[Cecil Acuff]

Fred,

    I went and got the real live R-390A manual to be sure there were no pin 
designation issues and there weren't.

My drawing shows no connection between pins 7 and 4 except through a 470K 
resistor isolating those two points in the circuitry. (R608)

Jumpering between pins 1 & 7, and 1 & 4, is doing the same thing just on 
opposite sides of R608....basically bypassing S-104 which appears to be 
where you problem is!

Cecil....
----- Original Message ----- 
From: "Frederick Bray" <fwbray at mminternet.com>
To: "Frederick Bray" <fwbray at mminternet.com>; <r-390 at mailman.qth.net>
Sent: Saturday, December 17, 2005 12:02 PM
Subject: Re: [R-390] More On Low Audio Problem


>I should have noted that it also works if I jumper terminals 1 and 4 of the 
>switch.  In the wide position terminal 7 connects to terminal 4. 
>Jumpering from 1 to 4 works regardless of whether the switch is in the wide 
>or sharp positions.
>
> TNX
>
>
>
>
> Frederick Bray wrote:
>
>> 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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