Vibrating tonearm Rockola 442

As I progress with my restoration Im looking to iron out a few issues, if indeed they are issues!

One thing I noticed is excessive (in my view) motor noise during quieter passages of music. I've ruled out motor grommets, theyre new and flexible, my idler is new, and Ive removed the speed conversion spring on the motor shaft, and instead now have a frequency converter delivering a 60hz signal to my TT motor instead. All have improved the noise to a degree, but what is apparent now is that the tonearm itself seems to vibrate excessively from the movement of the turntable motor.

For example with the turntable spinning, I can hold the tonearm, and feel moderate vibrations being transferred through to the arm (from the bearing housing I assume). Enough in my view for it to be picked up by the cartridge. Has anyone else noticed this on rockolas? Is there some grommet between the tonearm itself and pivot that's perished? Or possibly somewhere else I should look? Im considering adding some dampening material under the bearing housing, but not sure how effective this is.

This may be normal for these jukes, I know this isn't Hifi, but given the amount I can feel id expect not?

As ever appreciate opinions

Cheers
Adam

If it stops when the T-t motor is unplugged the motor itself may be internally unbalanced or touching some part of the chassis.

What is the condition of the idler puck?

Is everything properly oiled?

If you have a scope available, connect it to the same supply that feeds the motor (safest done through a transformer) and look at the waveform from the frequency convertor. Some produce a choppy waveform that can momentarily saturate the stator windings in the motor..

These idler-rim drive machines are never as quiet as the Seeburgs or later Rowe, but you should not be feeling vibration in the tonearm from the motor.

Rob/NYC

Hi Adam,
What color are the grommets ? If they are attached with screws, are the "spacers" installed ? I assume you oiled both ends of the motor ??
Ron Rich

The idler is a new one from those great folks at Stamann so has plenty of life left in it. The frequency converter I've been told puts out a square wave, but shouldn't be an issue due to the type of motor. I also had this issue before installing it so I don't believe that to be at fault.

The grommets are black and the motor hangs off them (held by washers and c-clips), so seems this motor doesn't require spacers. When I got the machine the grommets had already been replaced with clear / yellowy ones, I subbed these black ones in to see if they would make a difference and they didn't. I did strip down the motor and clean/reassemble/oil, so I guess either my motor is bad, or the other area I haven't considered is the turntable's bearing. I guess if that is worn it could be causing this. Should this be oiled or greased?

It has had oil but just the regular 3in1 motor stuff. I'll see if I can get some pics of it, perhaps you guys would know what a worn one looks like

IMHO, the motor grommets, on a RockOla, MUST be the (off) white type ! I have never been able to use the black ones successfully--they are too hard. Also, IMHO, you really do not want to get "Household-Multipurpose" 3 in One, oil, in the motor.
Ron Rich

Hi Ron, I did use the 3-in-1 "Motor Oil SAE 20wt", I've seen many a post from yourself warning against anything else.

Living in the UK its impossible to find, so I made a point of ordering some in a small bottle from the USA especially for this juke. I seem to recall it cost me around 20 pounds (around $31 at present rates)!

I do agree its a great oil for these machines, and can see exactly what you mean about it combining well with graphite grease, as is evident where I've added slightly too much on the gripper gears and a grey oily substance has oozed out.

Is there any test on the turntable bearing I can do? If I spin the deck by hand I do hear a slight metallic grinding sound, though this doesn't happen when driven by the motor.

I'll have a look at different grommets when I next place an order with Stamann or someone, which will likely be very soon

I have seen the motor bearings on that type motor become "egged shaped"--IMHO, there are two causes of this problem--lack of proper oil, and one of Rob's "geppetto friends" "adjusting", the idler spring (tighter), to overcome a poor idler wheel.
Ron Rich

I'm beginning to think my motor is shot. When I got the machine some gepetto had replaced the idler tensioner spring with a very strong one, as a bad idler repair I guess. I have no idea how long this was running like that so while I have the correct spring on it now, it's possible that it wore the motor bearings badly.

So I suppose my best course of action is a new motor and at the same time new grommets

Before changing motors, first see if there is any sideways play in the motor shaft. Hold the shaft and see if it is held firmly by the bearing, or not.

With motor running remove the T-t and hold the idler away from the shaft. Very often if there is excessive wear in the bearing the shaft will rattle when there is no pressure on it.

You might try opening the motor and checking for any sort of accumulated gunk on the rotor that might unbalance it.

Realistically, these machines are never going to be as quiet as a -good- home turntable. If you view some Youtube vids of R-O's you will hear hum/rumble.

Rob

Ok, managed to look at this last night. The source of the vibrations is the idler wheel, specifically the shaft it rotates on. If I touch the top of it I can feel it's vibrating a lot. Motor shaft has no play, almost silent without the idler against it.

Is there anything I can do to alleviate this? This machine has seen some gepetto-ing and did have an over tensioned idler spring when I bought it. I've since changed the idler wheel and the spring for the correct one.

Its also an intermix model that has had the speed change mech removed, so I wonder if this has left the armature the idler sits on at a less than perfect angle?

If the ID of the wheel is correct, and the OD of the shaft has become too small, the only "cure" I see is to replace the shaft--
If it is not "pointing straight up", that may be some of the cause--measure them both to determine what the problem iz--go from there-- Ron Rich