Diagnosing / repairing infrequent turntable RPM variance, very brief & infrequent speed / pitch changes-Technics SL-B1 Options

[Jenni28]

This Technics SL-B1 turntable - given by son - has very short (maybe 1 - 2 sec) & infrequent (1 or 2x / LP side??) changes in pitch - quite audible. It's one w/ a pitch / RPM adj wheel & strobe. Maybe this was a seriously cheap unit when new & basically P.O.C. No idea. Never had a pitch problem w/ the direct drive Dual that my son borrowed the cartridge from, but then, it wasn't decades old.

God knows how old this is (S.N. = 001 [kidding] - it's MS1116C161), & could be due to lubrication. Again, I'd expect it to occur more often.

The changes are over so quickly, can't look at the platter / strobe to see if shows anything changing. Have it hooked up to an UPS w/ AVR (automatic volt. regulator). Assuming that works, changes in speed shouldn't be due to voltage variations - but haven't checked voltage changes, much less monitored over 15 - 30 min period.

I believe it's belt driven (not had apart) & problem could be belt slipping, but I'd expect it to occur more often if it was. 99.9% of time, no audible pitch changes.

*** Have noticed the pitch adj (wheel) doesn't hold the speed constant. Could be # of reasons, incl. bad electronic components in rheostat. I used this type table in '70's, & most showed the markings fairly stable. Sure, there was slight variation back & forth, but not from markings dead still to moving at pretty good clip.

The strobe / markings on this Technics start to drift up / down from stationary, then maybe back to stationary for a few min. But I can't tell change in pitch when that happens. It's very touchy - a micro turn of the adj wheel may cause markings on platter to start spinning considerably. One's I used in '60's - '70's had much less sensitive adj wheels. ("You're livin' in the 60's, man!)

Haven't looked at the guts of adj wheel either - if it's mechanical variable rheostat or strictly electronic.
Any suggestions (toss it?)? Thanks.

[Jenni28]

Yes, eevan / Ivan, some persons from Europe sometimes pronounce his name ee-von (long 'e', as in green). I'm pretty sure they're variations of the same name, but not sure of the derivation or Evan.