Problems with Michell Gyrodec power supply

[Giac]

Hello everyone. I have been following the forum for some time but this is my first post. I own an early 80's Michell Gyrodec. I'm having trouble with the speed and smoothness of the platter rotation. I checked the possible presence of friction in the rotation of the platter and the motor without apparently finding any anomalies. My power supply is of the first type, the one that connects directly to the socket, and is for the PAPST alternating current motor which is fed at 24 V. I tried to measure the voltage between the three poles of the connector and the values obtained did not they convince me. In practice, between blue and green I find a stable 25 V, between blue and brown (to which the output capacitor is connected) I find 0 V, and between brown and green a voltage which at the beginning is between 20 and 30 V and then drops rapidly towards 0 V. This is the value that does not convince me. I think, but I have no evidence, that it should give me a stable voltage around 24 V, as in the blue-green. I'd like to know the values that are obtained with a well-functioning power supply to be sure that the rotation problems of my Gyrodec do not depend on the motor and to be able to adjust accordingly. Have any of you Gyrodec owners ever bothered to carry out this measurement? Thanks so much for every contribution.

 

[Another Johnson]

If the power supply has never been recapped, it is time. There may be other issues too, and these can be checked during the recapping service.

 

[mtemur]

Hello everyone. I have been following the forum for some time but this is my first post. I own an early 80's Michell Gyrodec. I'm having trouble with the speed and smoothness of the platter rotation. I checked the possible presence of friction in the rotation of the platter and the motor without apparently finding any anomalies. My power supply is of the first type, the one that connects directly to the socket, and is for the PAPST alternating current motor which is fed at 24 V. I tried to measure the voltage between the three poles of the connector and the values obtained did not they convince me. In practice, between blue and green I find a stable 25 V, between blue and brown (to which the output capacitor is connected) I find 0 V, and between brown and green a voltage which at the beginning is between 20 and 30 V and then drops rapidly towards 0 V. This is the value that does not convince me. I think, but I have no evidence, that it should give me a stable voltage around 24 V, as in the blue-green. I'd like to know the values that are obtained with a well-functioning power supply to be sure that the rotation problems of my Gyrodec do not depend on the motor and to be able to adjust accordingly. Have any of you Gyrodec owners ever bothered to carry out this measurement? Thanks so much for every contribution.

AFAIK papst is a two phase synchronous motor. There should be a transformer to convert line AC to 24VDC and a capacitor to produce second phase. When capacitor gets toast motor tries to run only with one phase with low torque. If that's what you're facing then replace the capacitor with a new one. Preferably a film type cap with same mfd rating.

 

[Giac]

Thanks everyone for the replies. I tried replacing the capacitor but nothing changed. So I ask you, if I disconnect the capacitor and then measure the AC voltage at the output of the secondary transformer where the cables are welded, what values should I detect? If between blue and green I get stable 25-26V without oscillations should I get the same result between brown and green or not? I would like to understand how the AC comes out of the transformer independently of the capacitor. Thank you

 

[microstrip]

AFAIK papst is a two phase synchronous motor. There should be a transformer to convert line AC to 24VDC and a capacitor to produce second phase. When capacitor gets toast motor tries to run only with one phase with low torque. If that's what you're facing then replace the capacitor with a new one. Preferably a film type cap with same mfd rating.

Well, as far as I remember from my old Gyrodec it uses a Papst 24V AC synchronous motor with an outer rotor. The transformer supplies 24 VAC and the capacitor is inserted in series with one the phases to create the 90 degree out of phase. Most probably you just need a new capacitor - but altough electrolytic it should be a bipolar, as it is inserted in series with the 24 VAC. It is an excellent motor - I used it with a sinusoidal generator connected to a Quad 405 to drive the Forsell when its controller was unstable - too many time unfortunately. Michell sold an advanced power supply doing just the same.