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Diagnosing / repairing infrequent turntable RPM variance, very brief & infrequent speed / pitch changes-Technics SL-B1
Jenni28
post Jan 23 2011, 23:58
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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.
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DVDdoug
post Jan 24 2011, 20:15
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That's a strange symptom.

QUOTE
It's very touchy - a micro turn of the adj wheel may cause markings on platter to start spinning considerably...

...Haven't looked at the guts of adj wheel either - if it's mechanical variable rheostat or strictly electronic.
This could be the source of the problem. It's probably a Potentiometer (rheostat). A noisy/dirty pot can usually be repaired with some Tuner/Control Cleaner. Sometimes, just working the pot back-and-forth several times can help, but it's best to use some control cleaner. (i.e. If you've ever had a noisy "scratchy" volume control, this could be the same kind of problem.)

Otherwise, the belt is probably the most common "failure" or "wear" item. And/or the lube in the bearings may have become gummy. I assume the "B" means "belt". I had a SL-D1 which was direct drive, and I still have an SL-D3 direct drive.
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Posts in this topic
- Jenni28   Diagnosing / repairing infrequent turntable RPM variance   Jan 23 2011, 23:58
- - DVDdoug   That's a strange symptom. QUOTE It's ve...   Jan 24 2011, 20:15
- - Jenni28   Thanks. Yes, it's belt. Anyone know where I...   Jan 24 2011, 21:46
|- - DonP   QUOTE (Jenni28 @ Jan 24 2011, 15:46) You ...   Jan 24 2011, 23:05
- - DVDdoug   Another option is to transfer the cartridge to the...   Jan 24 2011, 23:35
- - Jenni28   QUOTE If it uses an idler pulley, then it's no...   Jan 25 2011, 01:50
|- - Glenn Gundlach   You mis-understand the concept of 'direct driv...   Jan 25 2011, 04:39
|- - DonP   QUOTE (Glenn Gundlach @ Jan 24 2011, 22:3...   Jan 25 2011, 13:41
|- - stephan_g   Old thread, I know. QUOTE (Glenn Gundlach @ J...   May 29 2011, 01:29
- - Jenni28   Glenn - I didn't misunderstand the direct driv...   Jan 25 2011, 17:25
|- - cliveb   Apologies for coming in late - I've been away ...   Jan 30 2011, 11:18
- - Jenni28   Thanks Clive, for the link. I wasn't familiar...   Jan 30 2011, 19:04
|- - eevan   QUOTE (Jenni28 @ Jan 30 2011, 19:04) You ...   Jan 30 2011, 21:04
|- - Jenni28   QUOTE (eevan @ Jan 30 2011, 14:04) Use a ...   Jan 31 2011, 15:29
|- - eevan   QUOTE (Jenni28 @ Jan 31 2011, 15:29) Whic...   Feb 1 2011, 22:42
- - Jenni28   Yes, eevan / Ivan, some persons from Europe someti...   Feb 2 2011, 02:49
- - Arnold B. Krueger   QUOTE (Jenni28 @ Jan 23 2011, 17:58) This...   Feb 2 2011, 13:42
|- - Glenn Gundlach   QUOTE (Arnold B. Krueger @ Feb 2 2011, 04...   May 29 2011, 05:46
- - Jenni28   Arnold, yeah, sounds like a grease spot on belt m...   Feb 2 2011, 18:03
- - Arnold B. Krueger   QUOTE (Jenni28 @ Feb 2 2011, 12:03) Arnol...   Feb 3 2011, 14:19


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