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My Rega Planar 3 turntable is belt driven. It has been a year in storage, and now the platter spins backwards. A Google search suggests that one of the motor capacitors is to blame.

I reckon I'll replace both, as the turntable is over 20 years old. But since this is a 220 V circuit, I don't feel comfortable basing my actions on assumptions, hence this question.

Here is a picture of the PCB that drives the motor.

The two components on the motor PCB

The PCB is driving a "PREMOTEC 9904 111 31813" 50Hz 110V synchronous motor, even though the turntable is rated for a 50Hz 220V line. (Am I looking at a capacitive dropper?)

These two caps are the only components on the PCB (Update: I also found a 1MΩ bleeder resistor hiding under the Rifa). In addition, there's the motor, and a mains switch, and that's the whole circuit.

Here is a picture of the traces:

The underside of the PCB

And here is the whole compartment. The white wires go to the mains switch.

The whole compartment

An attempt at a schematic:

schematic

simulate this circuit – Schematic created using CircuitLab

First, to get the yellow capacitor (C1) out of the way:

It is a Rifa that hasn't gone boom yet.

  • The top is marked 220n X2
  • One side (visible in the picture) is marked 275 V ~ SH
  • The other side is marked RIFA / PME 271 M / 40/100/56/B / 250VAC / K5

I suppose I can replace this one with any 220nF X2 class 275V rated mains filter cap, am I right?

The white one (C2) is harder.

  • The top is marked 220n K J0 (OR JO?)
  • One side (visible in the picture) is marked EVOX / MMK / 400-
  • The other side is blank.

So my main question is: What type of capacitor is this? Or rather; What type of capacitor is it safe to replace this one with?

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    \$\begingroup\$ No idea but serious respect just for having a Rega Planar 3 - I remember earlier RPs when they came out. Nice one. \$\endgroup\$ – TonyM Sep 23 '19 at 20:04
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MMK is a metallized polyester film capacitor.

220n is 220 nanofarads.

K is 10% tolerance.

It is rated for 400V.

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    \$\begingroup\$ Better make that 400 V AC. \$\endgroup\$ – Transistor Sep 26 '19 at 21:47
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It's an AC synchronous motor. The red and blue leads should both have same voltage applied to them, but with the phase 90 degrees apart, which is what C2 provides. The R1/C1 combo drops the voltage down and probably tweaks the phase or load a little better.

The manufacture datasheet for the motor shows a slightly different circuit, with a 6.8k ohm 2.5W resistor replacing R1/C1 to drop the motor voltage to ~120V and C2 remaining the same. I have an early 80s Rega Planar 2 and it has a 12k ohm instead of R1/C1. A larger than recommended value is used since the motor runs a bit smoother with the lower voltage (around 80-90VAC).

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