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Decca DPS8: Motor Issue?
Decca DPS8: Motor Issue?
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Old 4th September 2013, 03:25 AM   #1
slor is offline slor  United States
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Default Decca DPS8: Motor Issue?

I've been restoring a mid-50s Decca DPS8 turntable for a friend, and I'll be damned if this isn't one of the most frustrating jobs I've taken on.

Every relevant component (electrolytics, tubes, speaker) has been replaced, the motor disassembled and relubed, motor mounts replaced. But speed is erratic, and the motor runs very hot.

I saw that the motor was rated "90V, 60Hz" and as an experiment, I subbed in an identical motor (but rated 117V).

Still runs hot, and eventually erratically.

I'm going to try dropping resistors on the motor circuit, but it's a bit of a shot in the dark. Does anyone with an education have a better suggestion?

Many thanks,
Seth
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Old 5th September 2013, 12:05 AM   #2
kevinkr is offline kevinkr  United States
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Decca DPS8: Motor Issue?
Does it run hot out of the turntable? What sort of motor is it? Synchronous or shaded pole induction with provisions for variable speed (adjustable)

Are you sure the table is up to snuff mechanically?

This would probably be better off in analog source so I will move it there.
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Old 5th September 2013, 12:13 AM   #3
kevinkr is offline kevinkr  United States
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Decca DPS8: Motor Issue?
Should you come up empty here try Vinyl Engine | The Home of the Turntable - you have to be a member.
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Old 5th September 2013, 12:40 AM   #4
slor is offline slor  United States
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I believe it is a synchronous motor; speed change is effected by altering the position of the idler wheel against the stepped capstan.

After further testing, I found that both motors run quite hot outside the turntable (both run off a variac at correct voltage, and removed from the mounting plate so as to remove that as a culprit).

So I'm going on the assumption that both are, to put it unscientifically, fried. I'm sad, as the 117V motor was a spare, and I believe was strong. For that matter, the 90V motor seemed strong when I first serviced the turntable. I can't think of anything that I did to change this, but evidence suggests otherwise.

Sadly, at this point, I think the turntable is junk.

Many thanks,
Seth
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Old 5th September 2013, 08:56 PM   #5
kevinkr is offline kevinkr  United States
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Decca DPS8: Motor Issue?
One last shot, and service the motor bearings as explained in the TD124 thread. Check alignment as well. See if motor runs hot when everything not tightly bolted together.
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Old 5th September 2013, 09:56 PM   #6
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
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When the motor is out of the chassis, can you spin it without any friction?
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Old 6th September 2013, 02:06 AM   #7
slor is offline slor  United States
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Yes, the motors (both the 90V and 117V models) spin fine. But after 10 - 15 minutes powered up, they are both very hot.

When I disassembled them initially, I cleaned the shafts with a clean rag, then poured a few drops of sewing machine oil into the felt surrounding the plain bronze bearings.

Kevin, thanks for the pointer. I am poring through that very long, but very informative thread now!
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Old 6th September 2013, 03:33 PM   #8
kevinkr is offline kevinkr  United States
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Decca DPS8: Motor Issue?
Are they plain bronze or sintered? In any event either way all old lubricant should be removed.

Can you post a few pictures of these motors? Trying to figure out if the rotor is at the root of the issue.
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