Under construction
When removing the platter it is essential to ensure that you do not overstress the main bearing. The easiest way to ensure this is to shim the platter off the main chassis so that the bearing shaft is no longer in contact with the thrust pad. I use short pieces of 4mm thick hardwood - 4mm x 20mm hardwood strip is easily available from the local hardware shop.
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Shims in place under platter.
If the platter / spindle interface is in good condition a gentle tap with a wooden mallet will free the platter. If you don't have a wooden mallet use a small block of wood on the top of the spindle and tap the wood with an ordinary hammer. If this fails to free the platter apply gentle heat to the platter - the platter is aluminium and the centre boss is bronze both of which have greater coefficients of thermal expansion than the steel of the spindle, so the connection will become looser as the temperature rises. Don't get it so hot that the paint blisters.
Platter off showing shim placement.
Having removed the platter, carefully turn the chassis upside down NOT PUTTING ANY WEIGHT ON THE CONTROL LEVERS as they are very fragile and ludicrously expensive. If you do break one see later regarding making your own replacement.
Remove the speed control linkage from the adjustment knob shaft and detach the three small springs which attach the linkage to the brake shoe. Detach the power cord from the motor. Now turn the chassis right way up and support it so that the weight isn't entirely on the motor housing. I use a couple of old textbooks for this. Undo the three main motor mounting screws.
Motor mounting screws partially removed.
Now lift up the chassis leaving the motor behind.
Remove the split pin from the eddy current brake “shoe” mounting and remove the shoe itself. Remove the frame from the motor by taking the circlips off the ends of the spring locating pins then removing the pins themselves. Remove the pulley and the eddy current brake disc by unscrewing the grubscrews a turn or so. Assuming the eddy current disc is nicely centred it is a good idea to loosen only three of the screws and mark the fourth. When re-assembling, leave the marked screw where it is, tighten the opposite screw lightly first, then tighten the other two equally.
The motor is constructed as a clam shell, with the two halves held together with through studs and nuts. Remove the two nuts from the bottom of the motor and the two screws securing the junction box to the motor housing. Take off the bottom half of the clam shell off then withdraw the rotor and shaft.
The motor shaft bearings are small sintered bronze spherical sleeves - one mounted in the top clamshell and one combined with a thrust ball assembly in the bottom clamshell. The bearings are effectively self oiling – the porous bronze “wicks” oil from the felt pads supporting them. You may however find that the oil has turned to varnish after fifty years in which case you need to disassemble the bearings. To do this drill the inner heads off the 2.5mm copper rivets with a 3mm drill. Do not drill into the motor casing.
The two top rivets have been drilled, the lower two are still entire.
Punch the rivets out using a 2.4mm or 3/32" punch. Remove the sinters , the semi-mythical oil felts and the placement springs. If the felts are still soft and pliable squeeze the oil out of them and soak them in new oil. If they have become stiff the oil in them has oxidised and will need to be dissolved away. I soaked mine in warm kerosene and GENTLY worked the felts to dissolve the oil. Squeeze out the kerosene, soak in oil, squeeze out the oil and resoak. If the oil in the flets is varnished the oil in the sinters will be useless so these will need cleaning too. I heat the sinters using a hot air gun, wipe off the oil that weeps out then drop them into a kerosene bath. Repeat. After this I soak the sinters in liquid propane - this is tricky and dangerous but it works. I move them straight from the propane bath to an oil bath where the propane evaporates and draws oil into the pores in its stead. Here's what the disassembled motor looks like:
Note the difference between the two felts - the lower one has been cleaned, the upper one is as removed. The dark specks are varnished oil. Clean all the motor parts very carefully with a soft clean cloth before reassembly. Any stubborn grunge can be removed by cleaning with a lightly oiled cloth – I use “prolink” bicycle chain lubricant for this, it does an excellent job.
Reassemble the motor by reversing the above procedure. When the motor is correctly reassembled it will run freely with very little noise. If it rattles you've done something wrong or the motor is out of balance as mentioned above. This is probably the time to call for specialist help.
Before reattaching the springs, check them over. The top springs are 16 coils of .033” wire and the bottom springs are 18 turns of .037” wire. All of the springs should be close coiled - for the motor to align properly with the turntable it is imperative that the springs in each set of three match. Any that are stretched should be replaced – if you can find exact copies of the originals good luck. If the rubber sleeves are perished use short lengths of silicone tubing with ¼” inside diameter.
When reattaching the pulley and the eddy current disc they must be exactly centred on the shaft - if you lack the means to check runout it might be best to get a local machine shop to do this. Mount the eddy current brake “shoe” back on its post. Mount the reassembled motor unit back in the chassis and check again that it runs smoothly and quietly. A good visual check is to run the motor with the platter removed and check that there is no blurring. If the edges of the eddy current disc and the pulley stay crisply visible while the motor is running then everything's OK. If they're blurry, something's out of whack.
Here's a rough drawing of the thrust bearing assembly:
I decided to make my own replacement switches and thought I might as well make them unbreakable. Accordingly I made a small silicone mould, using an unbroken switch, and filled it with carbon loaded epoxy resin with a woven carbon fibre epoxy base through which I inserted a stainless steel shaft made from a cut down 1/4 inch stainless steel bolt.
The main culprit with electrical noise is the power switch and associated suppressor cap but if you use an external power supply this is very easy to work around. Detach the suppressor capacitor and throw it away. I know, I know, I said you need to keep everything so that you can return it to original condition but there has to be an exception somewhere. Even if you do reverse this mod you should replace the suppressor cap with a modern switch transient suppressor such as a Roxburgh XEB1201.
Open up the switch mechanism and unsolder the two wires from it and remove the rest of these wires. In their place you need to solder in a wire from the +12V supply and a return to the drive terminal of the switch relay for the power supply. This means that there is now no AC switching above the plane of the TT chassis to cause electrical noise.