[R-390] R-390 Audio Gain

[Anthony Casorso]

Just some feedback on this problem. I was in the process of making some sensitivity measurements when this weird stuff started. I had the receiver sitting on a couple of pieces of 2x4 to keep the radio up off the bench and the bottom cover was off.  Based on Steve's comment about the electrolytic, I decided to tip the radio up on it's side. When I did that, I saw J620 a bit cocked. This is one of the two plugs going into the audio deck and is the one that carries the wires for the gain controls. I pushed it back into place and then took out C603 (the electrolytic that might allow cross coupling between the line and local audio circuits), C603 had some signs of leakage around the base but the caps check just fine for leakage on the cap checker at rated voltage. I ordered new ones anyway.
But, since putzing around in there, the problem has not reoccurred. I checked the grounds and they seem fine. In fact the gain pots are grounded whether or not J620 is plugged in. Looking at the schematic, I can't see how a loose J620 could cause the symptom. It's a mystery. Maybe the ground pin of C603 was making poor contact due to the small amount of leaked electrolyte. It didn't look like it got down to the pins but I'm reaching. The problem occurred several times after running for an hour or more over a period of several days. Nothing since I tipped it up and messed with it. It is still on it's side. Mazybe I should leave it like that :) ?
Tony


> From: stevehobensack at hotmail.com
> To: r-390 at mailman.qth.net
> Date: Tue, 1 May 2012 19:49:37 -0400
> Subject: Re: [R-390] R-390 Audio Gain
> 
> 
> I had a similar situation with the local gain. The volume wouldn't go quiet. Later I noticed that the line gain would silence the speaker and it wasn't even connected to a speaker. I found the problem with a bad (open) electrolytic cap in the audio deck. It was connected to the
> 6ak6 screens and common to them, the audio was mixing between the two audio output tubes.
> Steve N8YE
>  
> 
>  		 	   		  
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