Garrard Synchro-Lab motor advice please

[Mr_H_RetroTech]

I'm working on a SL95 and found a motor problem. The motor has a rattle at all speeds. However, if I run the motor on its side the rattle stops - it only makes the noise when the motor is running in its correct orientation as mounted on the deck's chassis.

I noticed there is a metal ring around the drive shaft positioned between the stepped spindle and the rotor. The ring is not attached to anything so spins with the motor but, as it's not attached to anything, it rattles inside the motor frame. I've not been able to remove the two screws that secure the motor frame together.

I have attached a photo to try to show the ring - it's the grey item indicated by the circle and arrow.

Before I attempt to dismantle the motor (the two screws are stubbornly resisting any attempt to remove them) I wondered whether anyone has experience of this issue or advice on what the ring is and why it seems to be simply sitting unattached around the drive shaft.

[Nickthedentist]

If it’s like the SP25/iv, it should be glued to the rotor, and the glue has failed.

[Beobloke]

The rotor is in two parts and it sounds like the glue has failed so they’ve separated.

Common Garrard fault!

[Mr_H_RetroTech]

Thanks chaps. That makes sense.

Just need to work out best way of removing the two screws that hold it together. So far they are refusing to budge

[Herald1360]

Try heating the screws with a soldering iron. If you can do it near the threaded end, so much the better.

[Mr_H_RetroTech]

Thanks to eeryone who has responded with advice so far. Here is an update on my motor question.

I did apply some heat to the screws and managed to loosen them. So, dismantled the motor and discovered the 'rattling ring' appears to be a balance weight. It was indeed secured to the rotor with adhesive in the form of a sticky tab which had dried out and become detached. Hence, loose metal ring and rattle.

The weight has a few drilled out sections which appear to be how it was balanced by removing some mass in a particular quadrant in similar fashion to balancing a car's wheels by adding/removing weights. I used a general adhesive to reattach the weight. However, although the motor no longer rattles it does have a slight wobble on its mountings - I suspect this is due to the weight being 'out of balance'.

So, next question is 'Any advice/guidance on rebalancing the motor?' especially without access to any specialist kit.

[Nickthedentist]

I think it's more than a balance weight, but either way, it's usually possible to stick it back in a correct-enough position by looking at the pattern of the old adhesive to determine which way round it goes on its axis, then centralising it by eye.

[Mr_H_RetroTech]

Originally Posted by Nickthedentist

I think it's more than a balance weight, but either way, it's usually possible to stick it back in a correct-enough position by looking at the pattern of the old adhesive to determine which way round it goes on its axis, then centralising it by eye.

Thanks for your comment but, I'm not convinced it's critical to basic operation as motor works regardless of the presence of the metal disc. I wonder if anyone in this forum has experience of the Garrard motor design?

I did try your suggestion about orientation but the only witness mark is the shadow of the original square sticky pad on the rotor. There is no corresponding mark on the weight to align with. I suppose I could trial and error but that will involve repeated sticking/unsticking the weight.

[Mr_H_RetroTech]

Found this old thread (2006 - 2018 https://www.vintage-radio.net/forum/...d.php?t=146526) which addresses the problem of the balance weight. I don't own an oscilloscope so tried the suggested balancing technique by eye. Weight reattached and motor runs with no discernable vibration - at least not by my 'seat of pants' assessment.

https://www.vintage-radio.net/forum/...d.php?t=146526

Will see how the motor performs while installed in the deck.

Thank you to everyone for the helpful comments.

[Mr_H_RetroTech]

Found this thread (2006 - 2018 https://www.vintage-radio.net/forum/...d.php?t=146526) which addresses the balance question. I don't own an oscilloscope so had to balance by eye and it seems to have worked. Motor runs with no discernable vibration.

I will reinstall the motor into the deck and monitor how it performs.

Thank you to all who offered advice.

[Nickthedentist]

Impressive, I don't remember seeing that thread before. Well done!

Note that Gene, forum name GP49000 is an absolute expert on Garrard autochangers, and describes that loose part as a "permanent ceramic magnet ring".

This thread, to which he contributed the vast majority of posts, is well worth a read: https://www.vintage-radio.net/forum/...ad.php?t=89840

Cheers,

Nick.

[Mr_H_RetroTech]

Thanks Nick, I read that thread with much interest - an excellent history of Garrad deck design and development. Still unsure about that ring, though. I have 2 synchro-lab motors now and that ring, which keeps detaching from the permanent magent rotor, is definitely some kind of metal alloy. I found the attached magazine article on the web that describes how the synchro-lab motor design came about and how it works. You can just see the balance weight attached below the permanent magnet synchronous rotor of the motor in the diagram.

All fascinating stuff.

[Nickthedentist]

Fascinating indeed, thanks for posting!

Maybe the SP25/IV motors I've seen are a bit different and lack this thin alloy ring?

[Mr_H_RetroTech]

Originally Posted by Nickthedentist

Maybe the SP25/IV motors I've seen are a bit different and lack this thin alloy ring?

Could be. I recently refurbished a SP25 Mk3 and didn't notice a similar ring on its motor.