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Old 20th December 2011, 11:15 AM   #11
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Old 24th February 2017, 08:13 PM   #12
ungie is offline ungie  Canada
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I'm bumping this old thread in case there are still some SFP-1 users around, and the schematics are already here for viewing. I have had an SFP-1 in my main system for nearly 15 years now and it has been rock solid, until a couple of weeks ago. I have always used the MC input and have never switched it to MM. Recently I have been hearing a random popping and crackling in the left channel only. My first thought was a bad tube as the ones in the unit have been there for over a decade. I tried re-seating all of the tubes, no change in the noise. I then swapped the left and right channel tubes, but the noise still remained in the left channel. Strange. I then cleaned the MC/MM internal switches on both channels, cleaned the tube sockets and pins, but there is still noise in the left channel. Now I'm thinking it's not likely a tube issue. To confirm this I switch both channels to MM mode and there is no noise. OK, on to the MC FET stage for the left channel. I first replaced the B+ supply resistor that drops to the B+ to ~10V, no change. I then swapped out the J310 FET with a new replacement, still no change. Now I'm confused as to what the issue could be. I touched up all of the solder joints in that section and it did not help. Now I'm down to replacing all of the resistors in that stage, but before I do I'd like some guidance as to what might be the cause. Is it in any way possible it could still be a tube issue, even though they are quiet in MM mode? The MC signal goes through the same stages, so I'm not sure how that could be.

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