For some time we have a problem with noise and crackled sound from ALPS master att. on 651..Yesterday I took it out from master section, unsolder all wires, and disassemble all decks with ceramic plates...There are a lot of dirt inside on contacts and wiper...all contacts are cleaned with isopropyl alcohol,shaft is lubricated with silicone oil and all this is assembled and put inside 651, nice weekend job...after all, crackled sound is gone, noise is gone and now I have clean master att. which is like new!!!
Care must be taken with ceramic plates, resistive film is laser cutted on ceramic, and that resistive part do not clean with isopropyl alcohol, only gently wipe with dry hygienic stick...
Cheers!
Raf
Audioplatinum Service