From: @noway.com   
      
   Jack wrote:   
   > Mark Zacharias wrote:   
   >> "Jack" <@noway.com> wrote in message news:ju1pmu$l85$1@dont-email.me...   
   >>> Jack wrote:   
   >>>> Mark Zacharias wrote:   
   >>>>> "Jack" <@noway.com> wrote in message news:jtqirc$g96$1@dont-email.me...   
   >>>>>> Mark Zacharias wrote:   
   >>>>>>> "Jack" <@noway.com> wrote in message   
   >>>>>>> news:jtnp3c$dcf$1@dont-email.me...   
   >>>>>>>> Jack wrote:   
   >>>>>>>>> After a week of playing with no problems, the right channel went   
   >>>>>>>>> out.   
   >>>>>>>>> It   
   >>>>>>>>> was the left channel previously. I was dismayed until I remembered   
   >>>>>>>>> that,   
   >>>>>>>>> when I reseated the output trannies, I switch them, left for right.   
   >>>>>>>>> I   
   >>>>>>>>> was further heartened when that same trick of switching off the   
   >>>>>>>>> speakers   
   >>>>>>>>> and turning the volume up to max brought the sound back. Since there   
   >>>>>>>>> are   
   >>>>>>>>> a pair of outputs in each channel, switching one of them again and   
   >>>>>>>>> waiting to see which channel goes out next should tell me which   
   >>>>>>>>> tranny   
   >>>>>>>>> is bad.   
   >>>>>>>> After switching back one pair of the output transistors, the PNP's,   
   >>>>>>>> NEC   
   >>>>>>>> B539A's, the problem stayed in the right channel, so I replaced the   
   >>>>>>>> right channel NPN, an NEC D287A with an NTE284. It's playing fine at   
   >>>>>>>> the   
   >>>>>>>> moment. I will button it up and consider it fixed until it tells me   
   >>>>>>>> it   
   >>>>>>>> isn't.   
   >>>>>>>>   
   >>>>>>>> Jack   
   >>>>>>> If you have not cleaned the relay contacts yet - you are wasting your   
   >>>>>>> time.   
   >>>>>>>   
   >>>>>>> Mark Z.   
   >>>>>> I cleaned the relays a couple of years ago when I tried to tackle this   
   >>>>>> the first time. Buffed the contacts with 1200 grit wet/dry sandpaper.   
   >>>>>> This time I tested the relays by bridging them when the bad channel was   
   >>>>>> out. didn't help. It wasn't the relay. The problem followed the NPN   
   >>>>>> output transistor when a swapped them left to right and right to left.   
   >>>>> OK, but 1200 grit...Wow. The coating on the contacts must not be too   
   >>>>> good   
   >>>>> anymore...   
   >>>>>   
   >>>>> I've used 6000 grit in the past and even that was too much.   
   >>>>>   
   >>>>> I'm not sure swapping the transistor really revealed the nature of the   
   >>>>> problem. As I'm sure you have seen, often we do something, it seems to   
   >>>>> fix   
   >>>>> the problem, then re-occurs later.   
   >>>>>   
   >>>>> You may very well have both channels cutting out at differnt times.   
   >>>>>   
   >>>>> I'm getting in on this late... have you cleaned the front panel   
   >>>>> push-button   
   >>>>> controls? They were NOTORIOUS for cutting out on this model.   
   >>>>>   
   >>>>> Mark Z.   
   >>>>>   
   >>>> Mark,   
   >>>>   
   >>>> The problem returned while playing an FM station. I clicked the Phono-1   
   >>>> button and then the FM button again and the channel came right back.   
   >>>> Something new to delve into.   
   >>> When the left channel went out again, applying slight pressure to the   
   >>> push button circuit board brought it back. I also noticed that when the   
   >>> channel was out, touching the metal prong in back that connects the   
   >>> preamp to the main amp for that channel produced a 60hz hum.   
   >>   
   >> Yeah - definitely spray some De-Oxit into those puchbutton switches.   
   >> Fortunately on that model, the rear of the switches are open and accessible   
   >> easily. Tilt up the rear of the unit and spray the stuff into the rear of   
   >> each switch, and work them in and out.   
   >>   
   >> Mark Z.   
   >>   
   >   
   >   
   > I did as you suggested, Mark. It took a while, as I was convinced, due   
   > to erroneous thinking on my part, that the problem was in the main amp   
   > section. I expected the bad channel to switch from left to right on the   
   > balance knob when I switched channels at the "pre amp out" "main amp in"   
   > RCA jacks in the back. It took me a whaile to see things correctly. At   
   > this point I switched channels between the push button input selector   
   > board and the tape monitor board to further isolate where the problem   
   > is, because after treating all the switches and pots, the problem   
   > presented itself again as diminished volume in the same left channel. I   
   > suspect that if the problem remains in the left channel, then the tape   
   > monitor switches are suspect. If the problem changes channel then the   
   > push button switches are suspect. This time I hope my thinking is right   
   > on this.   
      
      
   Well... after switching channels between the push button input selector   
   board and the tape monitor board, the bad channel switches from left to   
   right. This indicates to me that push button switches are the problem.   
   However, when I use the tape playback inputs on the back of the unit and   
   flip the appropriate tape monitor flip switch, the problem continues.   
   The tape monitor switch switches on the tape playback jacks and switches   
   off all input from the pushbutton switches. I will have to look at the   
   schematics and try to puzzle out this behavior.   
      
   --- SoupGate-Win32 v1.05   
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