rocknroller
Active Member
Have this SX-525 with several sound issues:
1) Immediately when turning on, there is a fairly loud "pop" sound. A lot of older devices make a sound when turning on but it just seems to be a little louder then one/I might expect. Anything to check there?
2) If I turn the bass knob immediately after powering on, i get a loud (enough) rustling sound, reminiscent of a really dirty pot. However the pots have been cleaned (several times, as well as all the tape switches etc etc). The rustling is unaffected by the volume or balance (turn out these are earlier in the circuit path, see diagram) and the source audio selected doesn't matter. The control amp board has had all lytics replaced (and several on the main amp board that follows as well). But the kicker is this rustling is ONLY present for the first 5-6 seconds, then disappears and ONLY present if I rotate the bass knob. If I don't touch the knob for 5-6 seconds, there is no issue. I've repeated this test dozens of times. If I wait 6-7 seconds before turning the bass knob, all is fine. But if I don't, it rustles. A dirty pot wouldn't care about the timing so I don't believe that is the root cause. It's as if some component is either warming up or charging up and at that point the issue resolves itself. The problem is worse in the left channel then the right, but seems present in both.
3) Lastly, In debugging effort to #2 above, I sprayed the input selector rotary switch. When I did and switched to Phono I got a terribly loud howl on both channels - slightly different frequency pitches and a machine like rat-tat-tat sound, each channel at a slightly different speed. On the oscilloscope it looks like a really bad repeating square wave. Eventually this sound cleaned up on it's own but as it did the pitch keep rising, volume diminished until it disappeared altogether. The phono source was playing through this but the howl was present whether or not anything was connect. I could "shut it up" with a rca terminator plug. I thought maybe I has sprayed a nearby board and that had some effect so the next time I made sure to spray only the rotary switch - same thing. While this really falls in the "Dr it hurts when I do this - Ok don't do that" I'm curious if anyone has an explanation as to why that happens when I do that?
1) Immediately when turning on, there is a fairly loud "pop" sound. A lot of older devices make a sound when turning on but it just seems to be a little louder then one/I might expect. Anything to check there?
2) If I turn the bass knob immediately after powering on, i get a loud (enough) rustling sound, reminiscent of a really dirty pot. However the pots have been cleaned (several times, as well as all the tape switches etc etc). The rustling is unaffected by the volume or balance (turn out these are earlier in the circuit path, see diagram) and the source audio selected doesn't matter. The control amp board has had all lytics replaced (and several on the main amp board that follows as well). But the kicker is this rustling is ONLY present for the first 5-6 seconds, then disappears and ONLY present if I rotate the bass knob. If I don't touch the knob for 5-6 seconds, there is no issue. I've repeated this test dozens of times. If I wait 6-7 seconds before turning the bass knob, all is fine. But if I don't, it rustles. A dirty pot wouldn't care about the timing so I don't believe that is the root cause. It's as if some component is either warming up or charging up and at that point the issue resolves itself. The problem is worse in the left channel then the right, but seems present in both.
3) Lastly, In debugging effort to #2 above, I sprayed the input selector rotary switch. When I did and switched to Phono I got a terribly loud howl on both channels - slightly different frequency pitches and a machine like rat-tat-tat sound, each channel at a slightly different speed. On the oscilloscope it looks like a really bad repeating square wave. Eventually this sound cleaned up on it's own but as it did the pitch keep rising, volume diminished until it disappeared altogether. The phono source was playing through this but the howl was present whether or not anything was connect. I could "shut it up" with a rca terminator plug. I thought maybe I has sprayed a nearby board and that had some effect so the next time I made sure to spray only the rotary switch - same thing. While this really falls in the "Dr it hurts when I do this - Ok don't do that" I'm curious if anyone has an explanation as to why that happens when I do that?
