Trying to fix mums turntable thats playing too fast

So the turntable in question is a pioneer rondo 3000x/y.
Everything seems to work fine except for speed.
My ac power is exactly 50Hz. And I've sanded off the 50 years worth of shmuts off the belt drive spindle...
But still to my ear its running noticeably fast. Basic app test shows 33.9rpm and 46.0rpm (both +/- 0.1rpm)
I cant see any adjustment pots on the motor
I tried to find a service manual but was unsuccessful.
And I've tried to google 'speed adjustment' but still couldn't find anything.
If there really isnt any speed adjustment, is it just a case of replacing dried out lubrication?
Thanks :)
 
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I suspect a picture of the motor and surrounding area (any circuit boards) might help. If it is a small DC motor then typically they can have presets located in the motor and accessible via holes in the rear plate. If so be careful not to use a metal screwdriver that can easily short to the case of the motor.
 
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I tried to fix a B&O Beogram turntable many moons ago (30ish years ago). It would run fine at the beginning of the record and then slow down. Lubing the bearings helped, but the problem came back eventually.

Anyway. My point is that I doubt lubrication is your issue. You could always try adding a small drop of sewing machine oil to the bearings and see if that helps. But more lubrication would seem to imply less friction, thus, higher speed.

Tom
 
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I've just spotted this in a write up on HiFi Engine. If this is correct then...

The 30cm (12-inch) turntable, equipped with quality MM type cartridge, synchronous motor, auto return and auto cut, gives you carefree stereo record playing enjoyment.

A synchronous motor is locked to the mains frequency although it can be slowed by using an eddy current brake but I've never seen that done on turntable, VCR's yes, but never a turntable. Your quoted speeds may well be within tolerance for a budget deck. The error is 2.7 % @33RPM and 2.2* % @45rpm

When measuring frequency of AC you perhaps need higher resolution than just '50' for example 49.54 or 50.47.
 
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If the motor can be tilted, this might provide some speed adjustment.
That gave me an idea... what about adding a thin flat belt of suitable width around the inner part of the platter that the main drive belt runs on to increase its diameter. I wonder what sort of effect say a 0.8mm belt would have on speed and whether it would alter W/F.
 
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If it's driven by a synchronous motor and the mains frequency is correct the motor should produce the exact required RPM. It then boils down to whether the belt sits correctly on the pulleys.

The mains frequency is usually pretty dead nuts on. If it's out significantly the generators at the power stations get really unhappy. I once built a clock where I used the 50 Hz mains as the time base. It lost/gained only a few seconds over the roughly six months between daylight saving time changes.

Tom
 
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The mains frequency is usually pretty dead nuts on. If it's out significantly the generators at the power stations get really unhappy. I once built a clock where I used the 50 Hz mains as the time base. It lost/gained only a few seconds over the roughly six months between daylight saving time changes.
In the UK that is true up to a point, the average over 24 hours is usually very accurate but can vary significantly at times of very high demand.

http://www.mainsfrequency.uk/fm-home

From above:

The GB mains frequency is nominally 50Hz. National Grid is obliged by its licence commitments to control the frequency within ±1% of 50Hz so it can fluctuate between 49.5Hz to 50.5Hz. However the normal operational limits are 49.8Hz to 50.2Hz.

And:
25 countries in Europe share a common transmission network that is synchronised across them all. Insufficient power generation in Kosovo, and Serbia's unwillingness to bolster capacity even thought it is legally obliged to do so, is believed to have led to the shortage of supply and so the average frequency has remained below 50Hz for some time. This has caused certain mains powered domestic clocks to run slowly with a typical error of 6 minutes since mid-January 2018.

This is the frequency right now here:

Screenshot 2023-08-22 175323.png


And a couple of minutes later:

1692723378006.png
 
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Sorry, i'll have to send photos tomorrow morning in a few hours. But from what i could see, the motor is wired directly to 240v mains. Its a big chunky boi. Outside ferrite lamination plates are like 2~3 inches wide. I couldn't see anything adjustable on first inspection.
I measured the mains freq with my multimeter. I think it was 49.9x or something. I thought close enough as its less than 50Hz anyway.
Perhaps a new belt is needed after all... Its probably 10+ years old now. Its only recently lost enough tension for the belt to slip off the platter when installing... Though i've just read from google that a loose belt is supposed to cause slow speed... Though its sounded this fast in recent memory, but it might have always. I'm not sure i'm just noticing it more now that i cant unhear it... From my first rpm tests shows a speed +3%... I'm not sure if thats abnormal, but to my ears my grim dark synth songs now sound like their sung by chipmunks lol.
I could sand the spindles a little more but thats probably a bad idea as i cant unsand them...
Would any aussie diyers know where i could source a replacement belt in sydney on short notice? Local pickup might be suitable. Unfortunately jaycar doesn't have the right size :(
 
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Yeah... And for a synchronous motor running at 3600 RPM with a 108:1 reduction gear for that magic 33-1/3 RPM the variation from 49.5 Hz to 50.5 Hz would result in a deviation of 33-0/3 to 33-2/3 RPM. A 1 kHz tone would vary by ±10 Hz. Is that audible? Probably if you switch fast enough between the two but for a slow variation or instantaneous "is this in tune?" test I doubt anyone would notice. Then again, I have not consulted science on this. Maybe humans have better pitch detection than I give us credit for.

For the 49.920 -> 49.982 Hz you show above I highly doubt anyone would notice a difference in pitch. Not thereby said that you could not measure a difference.

Tom
 
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That's going to be a traditional non adjustable mains synchronous motor a bit like this one. I came across an online comment somewhere suggesting your TT could be similar to a Pioneer PL12D Speed accuracy is quoted as 1% or better. There is a manual for the Pioneer on Vinyl Engine.

Screenshot 2023-08-22 181749.png


Screenshot 2023-08-22 181202.png
 
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your TT could be similar to a Pioneer PL12D Speed accuracy is quoted as 1% or better. There is a manual for the Pioneer on Vinyl Engine.

View attachment 1205286

View attachment 1205274
Yeah mines a little bit different. The motor design is quite a bit different too (looked like it had 4x coils or something)
Here's a video that shows the belt drive spindle:
Hopefully maybe i can shift the motor to add more belt tension?
Here's what it sounded like a year ago... And it sounds like its just as fast, if not now is even worse...
 
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You have it set to 45 RPM in the video. At least I counted 45 revolutions in a minute (and 33.3 revolutions in about 46 seconds). I just used a one-minute timer and counted the revolutions manually. If you use the strobe disc I bet you'll find that the 45 marks line up just about perfectly.

Tom
 
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