A MOTOR ISSUE

Hey Folks,

I've probably posted this a few years ago, but I have a 1965 Astro-Sonic with a between W602-W208 turntable. I thought the speed was rather off, so decided to tinker with it. This is the first motor I've seen with a fan blade mounted on the motor pole, I guess for cooling purposes.

Anyhoo, there was a little screw just out of reach of the fan blades, on top of the motor assembly. Dummy me, I though it was a speed adjustment and turned it...all hell broke loose, the WOW was horrible and now it takes about 20 minutes for things to settle down and the speed is fine. What is the purpose of this screw? IF I turn it too far, it will scrape against the part that is rotating. The screw has fallen somewhere inside the cabinet and I'll look for it at a later time. Just wondering about that little screw that I messed with. Any input would be greatly appreciated. Thanks so much...-BB

Bobby Basham
Tucson, Arizona

I can think of several different screws:

- One held the drive spindle on the motor shaft. Without it, the spindle is slipping.

- Two screws hold the motor bearing assembly together. With one missing, the bearings get out of alignment.

- One screw adjusts the height of the jockey assembly that changes the speed. Without it, the idler wheel moves up and down, contacting more than one speed step on the motor spindle.

- Three screws and three rubber spacers mount the motor.

Collaro motors do not have speed adjustments. If the speed gets off, either the lubrication has dried up, or the jockey assembly is misadjusted. Also look for accumulated crud on the inside of the turntable rim.

All Collaro motors after 1963 are combination induction and synchronous. They should not have speed troubles unless they need cleaning.

Collaro motors before 1963 are induction. They are purposely set slightly fast, and will slow down a little when the stack weight increases.

Thanks, Larry for the reply.

The problem is, there is still one tiny screw that is on top of the motor assembly. If you turn the screw in too far, it will grind on top of the fat part of the shaft below the bearing assembly. I think it kept the shaft from moving upward too far when power was applied 'cause I've noticed that some motor shafts do move slightly upward, not enough to affect the idler wheel placement.

I haven't opened it up since I did a recap and turntable cleaning years ago, but I think this motor may be round shaped and more enclosed, like smaller DC motors found in CD players and tape decks, hence, that little screw on the case which I mistook for a speed adjustment.

The turntable is an Imperial Micro-matic with the smaller platter and tall spindle. The 45 adapter has a hole in the top so it can be seated completely on the spindle. The back of the unit is bolted up like Fort Knox (replaced those old screws) and I'm not in the mood right now to deal with it... there are at least four other Maggies, amps and a few portables, cassette and reel deck machines near the top of the list.

Sorry for all the rambling. --BB

Bobby Basham
Tucson, Arizona

None of the units I have has that screw, and none of the manuals I have show that screw. Maybe it held the bearing in place.

I have the Conquest TSC-640 and 602 changers, and the Conquest TSC-640, 600, and 602 manuals.

I have never seen an adjustment screw on an induction motor for speed. They don't work that way. An induction motor's speed is set by the power line frequency and a slight amount of slip in the magnetic field. Here are the kinds of fine speed controls I have encountered on induction motors:

- Tapered drive spindle - This raises and lowers either the idler wheel or the motor to adjust the speed. This is the most common method. The drive assembly parts control the speed, not the motor.

- Eddy current disc - This moved a magnet closer or farther from a copper disc that spins on the motor shaft. Eddy currents in the disc slow down the motor shaft slightly when the magnet is moved closer.

- Special oscillator - Instead of using the power line frequency to set the speed, this uses an electronic oscillator to drive the motor. This is also used to set the record speed (33, 45, 78) speed. But this has never been used on a record changer.

- DC injection - Adding a DC component to the motor winding slows down the motor. I have one of these on my Conquest. It is basically a rheostat with a rectifier diode in parallel with it. This assembly is connected in series with the motor.

- Flyball governor - This was a brute force device used with some early electric replacements for spring motors. It used the existing governor in the spring drive, substituting the induction motor for the crank and spring.

- Pulse control - This consists of an ordinary TRIAC light dimmer (the kind you get at the hardware store) in series with the motor. A 7-watt night light is paralleled with the motor to make the dimmer work. But I have never seen it used with a phonograph. It was used for fan speeds.

- Ceiling fan speed controls. These are totally unsuited for phonograph use, because they interrupt the power on a slow (1 second?) cycle. That would make plenty of wow.