-september.org> 8f6e2952   
   From: zekor@comcast.net   
      
   Jack <@noway.com> wrote:   
   > 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.   
   >   
   > When the left channel drops out I can bring it back by pushing down from   
   > the top with a chopstick on the circuit board that contains the input   
   > selector buttons. I can then make it go out again by pushing up from the   
   > bottom on the same circuit board. After doing this several times, the   
   > channel comes back to stay... until it goes out again, which could be in   
   > the next ten minutes or ten hours. Also, pressing the input selector   
   > buttons at random also brings back the left channel. The puzzling   
   > behavior comes in when I switch channels at the PRE OUT/POWER IN jacks.   
   > If the problem is in the push button switches, the dropped channel   
   > should change from left to right, since the switches are upstream from   
   > the aforementioned jacks, but this does not happen. The dropped channel   
   > continues to be the left channel. I just don't understand how this could be.   
      
   I hope you got all switches sprayed by now. Vibration, pushing, heat, cold.   
   You use all and try to narrow it down.   
      
   Greg   
      
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