Rabco ST-4 not working

[MDP4800]

I bought it new in 1972 and have moved with it several times. The next to last time was to a house I lived in for 34 years before moving a couple of weeks ago. I did not use it that much. It had gotten geriatric in that when first powered up it spun (at 33-1/3 the only speed I used) slowly and then took a few revolutions to get up to the right speed.

When I moved, I did not want to take it apart and put it back together. I packed it up carefully and took it in my car not wanting to worry about how the movers might handle it. When I unpacked it, I was amazed to find that the platter drive belt was much larger than it was and would not longer work. Somehow or another it lost it elasticity during the move. I bought a new drive belt (on eBay from Germany) figuring that would take care of the problem. It is the right size. However, the platter does not turn. Without the belt on drive pulley spins. but not with the belt on. My guess is that either the motor no longer has enough oomph to turn the pulley and the platter or the unit needs some lubrication somewhere.

I have no idea what I can do. The manual says the platter bearing well has a reservoir filled with oil and no additional oil would be needed. The platter seems to spin normally when I rotate it by hand.

Has anyone run into this problem before? Any ideas about what I can or should do? After over 45 years, it does not owe me anything, but I have a sentimental attachment to it, so I would prefer not to trash it or try to sell it as a repair project and buy a new turntable.

Thanks for any ideas you can provide.

 

[Nat]

If the ST 4 is the all in one unit with the weird opening up in the middle dust cover, I would suggest looking at the motor. It is (or was on the two I picked up) a clam shell design, and a bump on the pulley might pop the two parts apart a bit, which I would assume would drop the coils somewhat out of the magnetic fields of the motor, weakening it. It also might be the motor capacitors. Certainly it would be worth cleaning and relubing all moving parts (since, if my memory is correct, the arm is driven off the platter, any problems with the arm are going to slow the platter down.
Good luck - when I had them running correctly, they sounded very nice, but it never lasted long at all. Loosening rivets and thin stamped and bent sheet metal weren't a recipe for a long stable life. But yours may be in better shape.

 

[MDP4800]

Thanks for the ideas. I'll see what I can do and report back one way or the other.

 

[MDP4800]

I don't think I have the type you described. Here is a picture and a thumbnail of the dust cover, which does not have a weird opening (the light is the flash). Is this the type you had in mind?

 

[Nat]

By weird opening, I meant opening in the middle, which I think yours does. I don't know of any other cover that does this.
Your table is the one I was thinking of, though I don't remember your resplendant brass motor pulley - I think mine were aluminum and rather similar in shape and diameter to that on ARs, which means bigger than the pulley the belt is on, but smaller than the lower part. Perhaps that is a sort of flywheel. But its been a decade or so, so my memory isn't clear.
There is an odd elegance to the ST 4's design - certainly not its appearance, which is somewhat agricultural, but the simplicity of the basic mechanism. The little wheel that drives the arm, and the coupling of the platter and the arm are examples of how to use the least complex means of achieving an end. I suspect that the electronic linear arm mechanisms may have better specs, but the history of electronic improvements on mechanical systems isn't all that encouraging (when people are using IPods as old as the ST4 I'll eat my words, and don't get me started on electronic versus mechanical cameras). And I wonder if the mechanical coupling of the arm to the base doesn't actually help with the immediacy of the sound, in the same way that idler drives seem to have grunt that belt drives do not.

 

[MDP4800]

Thanks again for your insights. I have worked on it a bit more and am leaning to a weakened motor, possibly due to the reasons in your first message, as the problem. I did clean off the parts and put a couple of drops off light oil in the well that the platter goes in. Without the belt, the platter spins fine and takes quite a few revolutions to stop. The drive pulley spins without the belt attached, but with it attached, it won't move at all. Even if I start the platter spinning manually, it quickly comes to a stop.

So if the motor needs some work or replacement, that is beyond my skill level, and I can't see how to get at it. I live in the Washington DC area, so if anyone near me is interested in either working on it for reasonable compensation or just coming and taking it, please let me know. I don't have the carton it came in, and I don't want to pack it up and ship it.

Time to start shopping for a new turntable. I have enjoyed using the ST-4 for over 45 years although not that often in the past few. However, I am not committed to linear tracking as my aging ears no longer can pick up the subtleties. I do like the idea of a belt drive for the reason you give.

 

[AdamAnt316]

I don't think the motor in the ST-4 had a lot of torque to begin with. I believe using the on/off lever is supposed to give the platter a bit of a push when shifting to the ON position in order to get it moving, though I have yet to investigate exactly how it's supposed to do so. Here's what my ST-4 looks like from the front, and what's under the pulley cover:

 

[MDP4800]

Quite a few years ago, I found it difficult to get mine to turn on when I put the lever in the on position. After getting it on one time, I unplugged the power cord and put in an on/off switch in the cord. That way I could turn it on. The idea that moving the lever gave the platter a bit of a boost may explain why mine started slowly and took a few revolutions to get up to 33-1/3. Every so often it did not want to start spinning, so I would turn it manually and it then it would get up to speed. That does not work anymore. No matter who fast I get it spinning, it quickly slows down and stops.

It is enjoyable hearing what other ST-4 users have to say and what their experiences are.

 

[Nat]

Is there a capacitor associated with the motor? If it's bad, that might be the source of the trouble.
I see from this picture that what i thought was some sort of small flywheel/pulley is actually the top of the motor.

 

[dr*audio]

I believe that motor does have a start up capacitor. It needs to be replaced.

 

[typesix]

I don't think the motor in the ST-4 had a lot of torque to begin with. I believe using the on/off lever is supposed to give the platter a bit of a push when shifting to the ON position in order to get it moving, though I have yet to investigate exactly how it's supposed to do so.

Yes, that's correct. I remember Stereo Review had tested it and made the statement about the on/off lever giving the platter a boost. At one point, I had considered getting one.

 

[AdamAnt316]

Yes, that's correct. I remember Stereo Review had tested it and made the statement about the on/off lever giving the platter a boost. At one point, I had considered getting one.

The whole turntable's a bit of a kludge, I think, but most (if not all) linear-tracking TTs back then were. Until Bang & Olufsen brought electronics to the concept with the Beogram 4000, all the linear-tracking arms on the market used either fully mechanical or electromechanical means to keep the stylus tangential to the groove. I'm glad I found mine, even if it's probably gonna be a major PITA to get it working properly, and keep it running afterwards.
-Adam

 

[dr*audio]

The only problem I had with mine was the rubber isolation mounts for the motor disintegrated and I could not find replacements that were resilient enough to damp the hum from the motor.

 

[hikerman]

The St-4 brings back a lot of memories. My first "high end" turntable, listed in Stereophile's recommended components. (It was subsequently deleted with no reason given). I bought mine mail order for well less than $200. When I got it, it didn't work. Playing around with it (manually spinning it and listening on & off to it) showed its' potential. One day, as I was about to send it back, it started working. I think the on/off switch had too much stiction and wasn't opening up. Once the switch was working properly it kept working and sounded great. Eventually problems developed. The most severe was the arm skating across the record. Never quite figured out why it would do it. Took it for service once and they couldn't find anything wrong. Make sure it's level is about all I got out of it. I think the rubber roller on the arm began to wear and may have resulted in some resonances taking place. At times it looked like the cartridge's stylus (always a Shure Vxxx) was being dragged from excessive friction. After a time I tired of the idiosyncrasies and bought a Thorens which was extremely reliable and great sounding also. In the 80s I began to hear about improvements being made to turntables so I thought I would do some experimentation before taking the plunge. I dragged the ST-4 out of the attic and started it up. The motor squeaked badly but after running it (and oiling it) the squeak gradually disappeared. I kept changing the cartridge and the sound kept getting better. I had the bottom cover off and the sound was much better, better than the Thorens. I tried playing around with the suspension some, but it was really the bottom cover taken off that made the most improvement. Now I thought if I can make the ST-4 sound this good, what could I do with the Thorens? I tried adjusting the Thorens suspension and never heard any difference. That design was stable. Now, however, I was a definite believer in the turntable making a significant difference in the sound, so I bought a Linn Sondek LP12, which was a significant improvement and never looked back.