I have a 30 year old Sansui SR222MKII turntable. The speed runs a little slow (about a note slow when comparing to the same track on a digital source). A strobe disc confirms this.
I have bought a used motor and installed it. Exact same speed issue. I tried a new belt, still no change.
On the circuit board in the turntable's under-carriage lies a resistor and a capacitor. Might the problem lie in these two components possibly needing replacement? I can't think what else might correct the issue. Adding a single wind of Scotch or electrical tape to the spindle results in the speed being much too fast. Both bearing and motor have oil.
TIA for any suggestions.
I have bought a used motor and installed it. Exact same speed issue. I tried a new belt, still no change.
On the circuit board in the turntable's under-carriage lies a resistor and a capacitor. Might the problem lie in these two components possibly needing replacement? I can't think what else might correct the issue. Adding a single wind of Scotch or electrical tape to the spindle results in the speed being much too fast. Both bearing and motor have oil.
TIA for any suggestions.
Hi,
Analysis is best before buying stuff. It may have originally run slow.
A different synchronous motor will make no difference nor will
changing any of the components that are driving the motor.
Belt thickness affects effective speed. But here I'd go for
spraying the pulley spinning with paint to increase speed.
rgds, sreten.
Analysis is best before buying stuff. It may have originally run slow.
A different synchronous motor will make no difference nor will
changing any of the components that are driving the motor.
Belt thickness affects effective speed. But here I'd go for
spraying the pulley spinning with paint to increase speed.
rgds, sreten.
Does your table have a built in stobe light for adjusting speed? Or are you using ambient flourescent? (Hey, I do it.)
Some tables have a 50/60Hz switch. The motor speed is determined by the power line frequency, so in the USA we use 60Hz, but in other parts of the world they use 50Hz. SOmething like that, a switch in wrong position?
Does this table even have a speed adjustment control?
Try this: take the belt off so the platter can turn freely. Give it a spin with your fingers. Does it spin freely, or does it slow right down quickly? 30 year old lubricants on the spindle could be drying up and dragging the speed.
Just thoughts coming to mind.
Some tables have a 50/60Hz switch. The motor speed is determined by the power line frequency, so in the USA we use 60Hz, but in other parts of the world they use 50Hz. SOmething like that, a switch in wrong position?
Does this table even have a speed adjustment control?
Try this: take the belt off so the platter can turn freely. Give it a spin with your fingers. Does it spin freely, or does it slow right down quickly? 30 year old lubricants on the spindle could be drying up and dragging the speed.
Just thoughts coming to mind.
Good questions. It's a 60Hz unit. No strobe, I'm using an incandescent lamp. Works well enough to see the strobe effect on the disc.
No speed adjustment (I haven't met too many belt drives which have this apart from the Dual models and 70's Marantz and Pioneers).
Platter spins so freely, that after a push, it doesn't stop for a couple of minutes.
No speed adjustment (I haven't met too many belt drives which have this apart from the Dual models and 70's Marantz and Pioneers).
Platter spins so freely, that after a push, it doesn't stop for a couple of minutes.
Hi,
FWIW I've never seen a 50Hz/60Hz switch on a turntable.
Only ~115VAC/~230VAC. If the motor is synchronous
driven off the mains frequency it will need a different
pulley to change operating frequency.
rgds, sreten.
FWIW I've never seen a 50Hz/60Hz switch on a turntable.
Only ~115VAC/~230VAC. If the motor is synchronous
driven off the mains frequency it will need a different
pulley to change operating frequency.
rgds, sreten.
A synchronous motor can't run a little bit slow. It will either run correctly or significantly slow (by pole slipping). The first stage has to be to find out what sort of motor it is.
It was just a thought. I haven't seen a 50/60 switch either, but I have seen various forms of strobe patterns for 50 versus 60.
It says here that it has a synchronous motor. You have two options: increase the pulley size, or feed it a slightly higher frequency.
PS the cap and resistor could be for motor starting - what are their values? Synchonous motors sometimes have to start as induction motors before locking onto the mains frequency.
PS the cap and resistor could be for motor starting - what are their values? Synchonous motors sometimes have to start as induction motors before locking onto the mains frequency.
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Here's a pic with the answers.
I am working on increasing the pulley size with spray paint.
I am working on increasing the pulley size with spray paint.
An externally hosted image should be here but it was not working when we last tested it.
The cap looks as though it might just be a mains filter. Resistor in series with a neon/LED ? maybe 😀
The CR looks more like a suppression network across the switch.
If the synchronous motor is magnet based, that could be the source of the problem: some types of magnetic alloys of the 70's and 80's were quite fragile and could easily be demagnetized; this would leave the starting mechanism (probably shaded poles) alone to drive the motor.
A good test would be to run the motor on a -30% voltage: if there is a difference in speed, this means that the synchronous operation is not reached
Hi,
Cheap shaded pole synchronous motors (e.g. PL12D etc.)
have dual windings and a switch for 110/220 VAC nominal.
Its most likely it simply by definition runs a little slow.
rgds, sreten.
Cheap shaded pole synchronous motors (e.g. PL12D etc.)
have dual windings and a switch for 110/220 VAC nominal.
Its most likely it simply by definition runs a little slow.
rgds, sreten.
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Hi,
No. Most likely its a high speed (4 pole) shaded pole motor,
with the necessarily tiny diameter motor pulley of the genre.
(loads of of old school japanese decks used the PL12D style motor)
rgds, sreten.
Efficiency of the motor is poor, but doesn't matter at low power.
Shaded pole does not need a phase shifted 2 phase AC supply.
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As I said in an earlier post, the motor is said to be synchronous. It could use a shaded pole to get it started.
The C and R could be snubbers on the switch? Tracing the circuit would help.
The C and R could be snubbers on the switch? Tracing the circuit would help.
Hi,
It is almost certainly shaded pole, which doesn't just
start the motor its fundamental to normal operation.
rgds, sreten.
The only answer needed is post #2.
It is almost certainly shaded pole, which doesn't just
start the motor its fundamental to normal operation.
rgds, sreten.
The only answer needed is post #2.
Here's the motor:
I have since managed to get the speed spot-on by following the earlier recommendation of paint-spraying the capstan.
An externally hosted image should be here but it was not working when we last tested it.
I have since managed to get the speed spot-on by following the earlier recommendation of paint-spraying the capstan.
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