Hey Frosty,
A couple of possible reasons for white (powdery?) residue on your heads.
Both are caused by the tape.
One is binder hydrolysis. Some tape formulations (IIRC Agfa/BASF) produce a white substance when the binder breaks down.
It would be accompanied by tape squeal and the machine might stop too.
The other is mold.
Bad stuff if you have a collection that you want to keep in good shape.
Not only does the mold produce spores which spread the infection to tape that are played on this machine, but they will cause drop outs and the mold will eventually ruin the tape itself.
Try and track down the offending tape(s), toss them, and clean your machine like never before.
Luckily cassettes are much better at keeping stuff like spores contained.
