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Vintage turntable running fast, any ideas?

I got a Pioneer Pl-12 turntable from a friend who had it stored away for years. I cleaned it up but have found that some voices have a higher pitch compared to the CD version. I tried the free strobe disks and they verified my fears about the platter turning (I assume) too fast. I also measured similar songs from CDs and albums, and the albums always finish sooner. From some rough time estimates, the turntable is running about 3% too fast.

Looking from the bottom side up on the turntable, there are no adjustments and very little electronics at all. The only electronics are: the motor with a few wires running to it; an enclosed switch to select 115/230 voltable, and a somewhat large capacitor (I think). The "capacitor" has a rating of 0.1 uF and some serial numbers.

I suspect the "capacitor" is old or burnt or whatever. I doubt the voltage switch is the prolem, nor the motor, but who knows?

Any ideas? I have a voltage meter so I can measure the usual volts, ohms, or ampere, but I don't have an oscilloscope to measure frequency.

Thanks for any ideas,
rrick
jameswei
883 posts
 
Could it be that one of your parts is a wrong-size replacement that got put in sometime a long time ago? It sounds like the pulley could be a too-big replacement. Or, the belt (which would have been the first thing to wear out and be replaced) could be too fat, making it not fit snugly into the "V" of the pulley, hence to rotate around a slightly larger circle than it should. Good luck.
tmcroy
25 posts
 
You could try wiring an ordinary light bulb in series with the motor - be aware that it needs to be in a safe place as they are reasonably easy to break and of course a broken light bulb is an electric shock hazard - also remember they give off heat.
The smaller the wattage of the bulb you use, the more it will slow things down and vice versa.
This is in fact simply a current limiting resistor. Used it on my old garrard 401 as the speed control on those is a magnetic brake, which does the sound no good at all. Eventually I got round to machining up a smaller motor drive spindle - didn't sound any better than the lightbulb!
vantageaudio
182 posts
 

This brings back dim, distant memories...!! The PL-12D was a good budget deck and was sold in competition with the Garrard SP-25 (MK whatever..) in the 1970's.

In the past we have worked on some of these decks for clients. Most of the speed problems originated from the motor and usually this was replaced. The original motor is no longer available but there is a motor kit still available that will revive the unit but it costs around £70 (approx US$100) in the UK, so it may not be a cost effective choice for you.

Belts are still available but this is unlikely to cause your fast speed problem.

We have a circuit diagram somewhere in the files and I'll see if I can locate it and double-check if there is anything you can check on, but dim memory tells me that other than reviving the motor there 'aint much else you can do.

Regards, Richard.

rrick OP
23 posts
 
It's funny how these threads have a life of their own and don't go in the direction you expect. My initial thought that it was some electrical problem within the turntable, but, most of the talk has been with mechanical issues.

Of all the suggestions, I think the thick belt suggestion is the one I plan to try next. I compared the current belt with a previous worn out one and sure enough it was much thicker. Once I get the speed correct, and get a stable disk strobe pattern, I'll check out if the motor has fast/slow problems. After that, its time to enjoy the thing or drop it off at the nearest thrift shop.

One thing I have learned here is the importance of a second source to compare things. (Now reread the above sentence until you understand it.) I only found the speed problem by comparing the record to a CD copy. After a couple of albums and CDs, something didn't sound right, and that helped me find the problem. In the process of switching the turntable between my main stereo system and the TV surround system, I've found that my much more expensive stereo system has a severe bass problem! Ah yes, this never ends, does it.
tmcroy
25 posts
 
Hi fi is usually a bottomless pit - but have you ever noticed that most musicains listen to things with the sonic elegance of a mice powered turntable using a 4" nail hooked up to an old tin can with a bit of string?
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