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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
rrick OP
23 posts
 
The turntable is belt driven where the pulley is connected to the shaft of the motor. I have cleaned the area where the belt rides on the pulley. I don't think the pulley is worn because this would cause the table to turn slower or possibly erratically.

I went back and took a closer look at the belt fit and it looked liked the belt was riding high against a wider shaft. I refitted the belt and made sure it is in the middle of its allotted region, and alas, no change.

You did give me an idea. If all else fails I can sand the pulley/belt area down a bit. This will cause the table to turn slower. Right now, the table runs faster for both speeds (33 1/3 and 45 rpm).

I am close to positively sure the table is running fast. I checked the table with the strobe disk, and the strobe pattern is moving in the same direction the platter is turning. In my book, this means the table is moving a little faster than expected by the strobe disk.
rwwear
2,692 posts
 
Does the other end of the belt go around the platter? It seems like there is an arm that moves the belt in and out when you change speeds if so, check it also.
marakanetz's avatar
marakanetz
5,473 posts
 
If your platter turns with the constant speed all you can do is to place arround the platter pulley rubberband making the diameter larger so decreasing the rotations of the platter. Try to "dress" different rubber bands so to get the most precise rotations measured with the strobe disk.

The other question is what is more reasonable to buy the strobe disk or another PL12?
william7
51 posts
 
You better hurry up and catch it but if you wait for a while it will slow down the older it gets
rrick OP
23 posts
 
There is an arm that moves the belt between two different diameters on the pulley. My theory was if it was getting in the way, it would slow down the turntable. Right now, it doesn't look like it affects the belt much.

If I want to physically change the dimensions of the turntable, I have two choices. Make the platter larger or the pulley smaller. Since the pulley is so much smaller, I probably sand it down.

What's weird to me is that the thing runs fast. I didn't expect to run into an old turntable with a hot to trot motor. I'll make sure is has lots of oil and let it run for a day or two. Maybe that will cool its heels.
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