Oracle Delphi motor can't achieve right speed... - diyAudio
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Old 29th August 2002, 12:11 PM   #1
diyAudio Member
 
Join Date: Jan 2002
Location: Italy
Unhappy Oracle Delphi motor can't achieve right speed...

I've bought on E-bay a used Oracle Delphi MKI and I've spent the last few months restoring and upgrading it.
Everything now works fine with one major exception: the motor.

No matter how much I turn the adjustment trimmers on the back of it, I can't get the right speed neither at 33 1/3 nor at 45 rpm.

In the 33 1/3 case, the speed is a little slower than nominal whilst at 45 rpm it's slightly faster than nominal. Please note that the speed achieved in either case is quite stable, without fluctuation or drift. Even the wow & flutter seem to be at a very acceptable level.

The adjustment trimmers in the back of the motor do work. They actually increase and decrease the speed within a range... except that the optimum speed is outside this range!

The fact that I can get very close to optimum speed without actually being able to achieve it suggests that some reference voltage/adjustment inside the speed regulator has gone out of tolerance. Also, I find it strange that the motor turns slightly slower than 33 1/3 and slightly faster then 45 rpm.

By the way, the voltage out of the adapter is right, I checked it with and without load, so it's not a matter of input voltage.

Does anybody know how to fix or replace this motor? Are there any suitable replacements? I wouldn't like to shell out $300!
Any suggestions?
Also, getting some more torque I think could improve the sound...

Thanks for your help.
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Old 1st September 2002, 12:13 PM   #2
dice45 is offline dice45  Germany
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m.parigi,
promised help:
i do believe your Oracle Delphi has a Pabst GS3809 as motor.

Below you can see a top view and a bottom view of it; i have three samples of it, one used up, one in use and one unused/NOS. I used the used-up one and the unused one to take the photo.

This motor is fed with either DC 27V or AC 20V. It has three pins called 1 2 3 to connect the speed control fine adjustment for 33 and 45 rpm.

On the bottom of the pix, (component side, right lower corner, solder side / top view, left lower corner; both located at the center of the pix'es bottom edge)you see a varaible resistor on the PCB. This resistor is the coarse speed adjustment; if you toy around with it, you should be able to get the motor speed plus/minus adjustable with the two fine adjustments connected to 1 2 3. Se also posts below, ask if you have further QQ.

One remark, i have no idea how Oracle connected the motor; my info is from own experience with this thing and from the original Pabst data sheet.
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File Type: jpg pabstgs3809_tv_bv_small.jpg (52.3 KB, 794 views)
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Bernhard
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Old 1st September 2002, 12:15 PM   #3
dice45 is offline dice45  Germany
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technical drawing with PCB connectors named:
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File Type: jpg pabstgs3809_dwg_small.jpg (55.5 KB, 733 views)
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Bernhard
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Old 1st September 2002, 12:21 PM   #4
dice45 is offline dice45  Germany
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Default How variable resistors for speed control (fine) should be connected.

Power supply for DC, 24 to 27 Volt is pad6 (plus) and pad7 (minus) (why not a battery, the motor loves this and you'll love the sonics)

Power supply for AC. connect to pad4 and pad5.

Speed control: pad1 is common, pad2 is 33rpm and pad3 is 45rpm
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File Type: jpg pabstgs3809_sch_small.jpg (12.0 KB, 710 views)
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Bernhard
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Old 2nd September 2002, 12:43 PM   #5
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Default It works...and it doesn't

Thanks a lot, Dice45. That's exactly the motor of my turntable!

I tried to turn the coarse adjustment trimmer and I've managed to get the speed right. So this problem is solved. Thanks again.

I've noticed, though, that the motor hasn't got a lot of torque and that in some instances there's a fluctuation (wow) of speed. I've tried cleaning the pulley and the platter and I've even replaced the belt, without any success.

Could it be that the motor is getting old and "tired"?
I gather that the spares aren't available any longer. If so, would you be available to sell the extra motor you have? Can you write me so that we can discuss the details?

Thanks,
Maurizio
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Old 5th December 2003, 02:19 AM   #6
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"I've noticed, though, that the motor hasn't got a lot of torque and that in some instances there's a fluctuation (wow) of speed. I've tried cleaning the pulley and the platter and I've even replaced the belt, without any success."

It is interesting you are having problems with your Oracle.

My father is having the same problem and I took a look at it at my shop.

I ran the circuitry through my o-scope and it seams to be working fine. I guess the motor is old and worn down.

If you find a motor or suitable replacement, let me know. It is a shame to
see such a great turntable turn into a doorstop.

tech
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Old 5th December 2003, 03:06 AM   #7
sreten is online now sreten  United Kingdom
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Location: Brighton UK
Check that the motor is free spinning - just may need a little oil.

If your really keen drill out the rivets and give the inside a good
clean and oiling.

Worth trying before resigning yourself to a new motor.

/sreten.
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Old 5th December 2003, 04:53 AM   #8
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Hi sreten,

Great idea, cannot wait to get to the shop to try it out. After many years on the dusty praire it would not be surprising if there is a family of dust bunnies in the motor.

This motor cannot start up and run, give it a spin and it will run fine.

Thanks for your help.

tech
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Old 5th December 2003, 06:35 AM   #9
sreten is online now sreten  United Kingdom
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Default A word of caution

If you are thinking of drilling out the rivets and cleaning it.

I've done this to one motor :

After drilling out the rivets there will be some way of vertically
supporting the spindle. In this case there were two friction
fit bushes onto the spindle that were captive in each half of the
motor. I got it apart easily enough but getting it back together
with the rotor the right height wasn't so easy.

/sreten.
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Old 5th December 2003, 07:03 AM   #10
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In my case I've determined that it's not the motor's fault, but the bearing's.
By removing the belt and turning the platter by hand I've determined that there's considerable drag, and this puts considerable strain on the motor.
Oddly enough, this appears to be a quite common problem with Oracle, because I called them for tech support and they were well aware of it.

In their words, in the bearing there are a couple of teflon bushings that over time tend to absorb some oil and "swell", thus increasing noticeably the drag.
Their solution (surprise, surprise) is to replace the bearing altogether with their new, improved MkV bearing. Too bad that it costs in excess of $300 and that it requires some machining of the sub-chassis at an additional $100 cost.

Anybody, ideas on how to avoid this?
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