[R-390] More On Low Audio Problem

[Cecil Acuff]

Of course another possibility is that the switch is inadvertently in the 
sharp position which would yield low, strange sounding audio as 
described....

Just a thought....

Cecil...
----- Original Message ----- 
From: "Cecil Acuff" <chacuff at cableone.net>
To: "Frederick Bray" <fwbray at mminternet.com>; <r-390 at mailman.qth.net>
Sent: Saturday, December 17, 2005 11:53 AM
Subject: Re: [R-390] More On Low Audio Problem


> 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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>
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