I pulled my 1978 Sansui BA2000 power amp out of the attic recently and fired it up after about 10 years of inactivity. Surprisingly it came to life and sounds superb at normal to high volume levels but during low passages and/or with the power amp's volumes turned down the sound will completely drop out (output meters drop too) until a louder passage occurs or I turn up the power amp's volume controls and then the volume pops right back up. It's happening to both channels but to the left much more often.
I plan to open it up and trace the audio with a scope but thought I'd ask in case someone recognizes the symptoms. I guess it could be as simple as the volume pots need some Deoxit.
Thanks in advance,
Rob
I plan to open it up and trace the audio with a scope but thought I'd ask in case someone recognizes the symptoms. I guess it could be as simple as the volume pots need some Deoxit.
Thanks in advance,
Rob
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Sansui BA-2000 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
Nope, Deoxit or chemicals won't fix this sort of problem unless there is some scratchiness in operation that is common to both channels. At around 35 years of age and regardless of whether its used or not, the electrolytic caps in there will be causing most problems. If they haven't already been replaced, you could even see this on a multimeter if you had the schematic and some understanding of how to proceed.
It's not a very complex or large circuit to work on, so a routine replacement of all the electrolytic caps (usually standing upright and always marked with polarity) is probably a good procedure whether it is the major cause of this problem or not. Use good quality, commercial quality parts like Panasonic FR, FM for small values and TSHA for the main (largest) ones. Others like Rubycon, Nichicon, United Chemicon also make good equivalents. If suitable ones are available as genuine parts at a realistic price, use them.
Nope, Deoxit or chemicals won't fix this sort of problem unless there is some scratchiness in operation that is common to both channels. At around 35 years of age and regardless of whether its used or not, the electrolytic caps in there will be causing most problems. If they haven't already been replaced, you could even see this on a multimeter if you had the schematic and some understanding of how to proceed.
It's not a very complex or large circuit to work on, so a routine replacement of all the electrolytic caps (usually standing upright and always marked with polarity) is probably a good procedure whether it is the major cause of this problem or not. Use good quality, commercial quality parts like Panasonic FR, FM for small values and TSHA for the main (largest) ones. Others like Rubycon, Nichicon, United Chemicon also make good equivalents. If suitable ones are available as genuine parts at a realistic price, use them.
Sounds like the protection relay has developed nice oxide layers on its contacts while in storage. If a compatible type should still be available you can replace it, otherwise these things tend to be fairly easy to open once unsoldered and can then be cleaned with contact cleaner and maybe some paper or similar. Avoid scratching the surface with sandpaper or worse.
After a decade on the attic, the smaller electrolytics also deserve a look though.
After a decade on the attic, the smaller electrolytics also deserve a look though.
Thanks guys. I do plan to replace all the caps and clean all the connections in the signal path. I'll take a close look at the protection relay too.
^ As sgrossklass describes above. Relays are a prime candidate. Run some paper soaked in iso through the contacts.
What happens is that the louder passages actually pass enough current to temporarily punch through the oxide layer.
What happens is that the louder passages actually pass enough current to temporarily punch through the oxide layer.
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