Sota Sapphire rebuild and motor issues - diyAudio
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Old 16th August 2014, 01:14 AM   #1
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Join Date: Oct 2011
Location: Arlington
Default Sota Sapphire rebuild and motor issues

Hey there guys. I just picked up an older Sota Sapphire from the 80s off that auction site that had "speed issues". Got it in the mail the other day and it was in pretty rough shape. The cord that attaches to the motor controls was partially detached. The bottom chassis is also made of MDF, so anywhere there was a load bearing bolt or screw that was stressed, it's busted.

The chassis is another issue I'll address in time, but I re-soldered the wires to the area of the switch and replaced a cap (with the matching value) that was out of spec. Fired it up and have a very "rough" sounding motor. There is some light scraping as if the pulley shaft is out of alignment, and the whole motor seems to shudder every now and then. It uses a Pabst motor (the "pancake" kind, I believe) with what seems to be a lead screw in the bottom of the thing that is as soft as butter.

I haven't thoroughly checked the 20 or so resistors on the board, but before I go on and potentially destroy it, I wanted to ask has anyone ever attempt to service one of these motors or encountered any problems they resolved? Any pointers would be appreciated.
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Old 17th August 2014, 03:32 PM   #2
AVWERK is offline AVWERK  United States
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Put a drop of Acetone on the slotted screw and wait a little, then start moving the screw back and forth to get it moving

You would adjust in if you hear a scraping noise.
I did this to one that was in bad shape also.
The up and down free play was too much on mine compared to 2 other SOTA,s I have.
This model is a early version without the cast metal housing of later versions. ( note the u shaped aluminum bracket )
If I get time, I will check the free up and down play with a dial indicator on the newer versions so you can get it close
Turning it in will get you started.

Regards
David
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Old 19th August 2014, 12:29 AM   #3
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Thanks for the response David. I managed to get that screw out from the bottom and peek inside the motor. With the pulley shaft inserted, I could see that it was pulling the lower bushing out of center causing the rubbing/scraping I heard.

I realigned it by sight, put a new set screw in, and turned it on. There was still a little rubbing so with a little sideways pressure on the spinning pulley, I was able to push it into better alignment. It is as quiet as a mouse now, and even with a stethoscope, I can barely hear resonance on the aluminum bracket.

I'd still like to know how much play I should have. If you get a chance to measure it, let me know.

Also, attached is a photo of the "upper" plinth. You can clearly see the coupling bolts have broken out of the MDF housing and were completely free. Over the weekend I put some together with hardwood and aluminum plate. I'm not sure if you can see the bottom, but the hex head bolt goes through a washer. Only thing that will give out now would be the screws holding it in place, but I figure it'll be good to go for another 30 years.
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Old 19th August 2014, 01:42 PM   #4
AVWERK is offline AVWERK  United States
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On my 2 Star tables with the casting style motor mount, the up and down free play is .004" and .006" on the other.

On the 3rd one and same style as yours I set it to .004" and the scraping went away. It originally had triple this dim.

Regards
David
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Old 21st August 2014, 01:09 PM   #5
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Well, maybe I spoke too soon. (There's a chance I had my stereo up too loud.) The noise is still there. The shaft is now centered and everything in alignment but I still have some friction with the shaft that causes the scrape.

Yesterday, I noticed if I turn the motor assembly upside down, the pulley shaft moves down (away from the bronze bushing) due to the vertical play, and the noise completely disappears. Question is, how did you adjust the vertical play, David? Adjustment of that set screw doesn't do much at all.

And is this thing supposed to have a thrust plate? I read a forum on a HK ST-7 that uses the same Papst 38.09, and some guys were talking about a thrust plate. There is no evidence of one in my motor. I can back that set screw out completely and see the bottom of the shaft.

FM
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Old 21st August 2014, 11:03 PM   #6
AVWERK is offline AVWERK  United States
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Maybe yours is defective?
I never took the screw out as I had no reason to.
Screwing it in solved my issue and can' t understand why yours would be different?

Regards
David
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Old Yesterday, 02:58 AM   #7
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Yes, it's possibly defective. I'll keep working with it to see what I can do. If I can't stop the friction, I may go ahead and open the motor up to see if there is debris of some sort causing the problem. I appreciate the help.

FM
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Old Yesterday, 10:11 PM   #8
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Join Date: Oct 2011
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Got it! A little trial and error and I was able to eliminate the noise. It seems the pulley shaft wasn't seated well. With a little coaxing, and a "tightening" of that set screw, the problem was solved. Speed appears constant and the friction is gone.

I know this isn't a woodworking forum but the Sota came with a light, honey oak plinth that had virtually no depth of color or character. It's good wood with some potential so I sanded it down and toned the wood with General Finishes Vintage Cherry dye diluted 1:1 with water. I've sealed with two thin coats of shellac and it's now a gorgeous dark amber. I'll rub a dark stain into it next to see if I can get the grain to pop a little, seal it, and I'll post a photo or two. Next step is just to put it all back together. It might be a keeper.
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Old Yesterday, 10:38 PM   #9
AVWERK is offline AVWERK  United States
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Glad you got yours running!
I also used a red dye on mine. It is African mahogany and I sprayed it with German lacquer and sanded between coats
Normally mahogany doesn't need anything but a clear coat, but it just pops with red dye added.

Regards
David
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