From: tim@bristolnj.com   
      
   On 6/28/2012 9:39 PM, Jack wrote:   
   > This is a great piece with one little problem. Often, when switching the   
   > unit on, the left channel is out, no sound. Turning the volume up always   
   > kicks it in. Often the volume has to be turned up severely to accomplish   
   > this so I tried doing it with the speakers switched off. Switch off   
   > speakers, turn volume up to max, turn volume down to min, switch   
   > speakers on, turn volume up a bit and the sound is back in both   
   > channels. In addition, after getting both channels to work, after 10 to   
   > 20 minutes, give or take 5, the left channel goes out again.   
   >   
   > This behavior lead me to suspect the volume switch, so I flooded it with   
   > switch cleaner and worked it, but to no avail. Problem persisted. Next I   
   > checked all the cold solder joints and found one that was loose. I hot   
   > soldered ALL the cold solder joints. Problem continued. Today I used   
   > some cables to switch the PRE OUT channels into the POWER IN channels,   
   > left to right and right to left. The next time the problem cropped up it   
   > was still in the left channel. This is telling me that the problem is in   
   > the left main amp section.   
   >   
   > Given the behavior described above I can only guess that a rise in   
   > voltage in the main amp produced by turning up the volume with the   
   > speakers turned off somehow corrects the condition causing this problem,   
   > but at the moment I don't know what this condition might be. I assume   
   > that with the speakers turned off there is not a lot of current flowing   
   > in the main amp when the volume is turned up, but that the voltage is   
   > increased. As I write this, a dawning suspicion presents itself and that   
   > is: the problem might be with a transistor, as they are voltage regulated.   
   >   
   > Next step is to open up the unit and do a visual inspection, hook it up   
   > to a pair of speakers and turn it on and attempt to compare voltages   
   > along the signal path of right and left channels of the main amp when   
   > the problem crops up.   
   >   
      
      
   My vote is for bad relay contacts on the speaker protection relay.  Try   
   tapping on the relay with an insulated rod, like a small stick while the   
   unit is on and the channel is out.  If tapping on the relay gets it to   
   come on, then clean or replace the relay.  You have to take the relay   
   apart to clean it properly.   
      
   	On the other hand, it could be other switches and controls being dirty.   
     Have you tried moving the speaker switches and tape monitor buttons   
   while the problem is there?   
      
   Regards,   
   Tim Schwartz   
   Bristol Electronics   
      
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