The TD124 Motor
My example came with a spare motor. The original TD124 motor is seen to the right of the turntable. The PO had trouble with too-fast running speeds and had replaced the motor with another. Unfortunately the fast running speeds persisted. For this page I will clean and lube the original motor to see if it can be re-used.
The motor type is a shaded pole induction motor. In the above photo the two phase coils are visible on either side of the large central opening. The different colored wires are for different operating voltages. Black for 100-120. Yellow for 125-150. Green for 220-250 volts. The red wires are for AC mains.
Looking inside the casings after many, many years of use and then many years of non-use. The lube reserve held within the felts has dried and turned to wax.
The bushings are contained within an assembly of felt pads, spring collar and cover. These are originally held in place with hollow rivets. To service the bushings the rivets were drilled out. I've seen photos of these motors far more gunked-up than this one was.
Take a look at the bottom end cap with the white plastic thrust pad. The small bearing ball rides between the pad and the countersink within the end of the rotor shaft. Wear is indicated by the indentation within the white pad.
Some of the parts. The white plated parts were allowed to soak in Berryman's B9 Carburetor cleaner. After 1/2 hour they came out free of crud and shiny. The carb cleaner can also strip paint. Caution is in order. Caustic skin irritant, eye melting acids! The bronze spring retainers were simply washed in lacquer thinner and wiped dry. On second thought, these could have also benefited from a soak in the carb cleaner, but they will be functional as is.
The sintered bronze bushings after the first cleaning. First the bushings were baked at 250 deg. F. A dark greasy substance oozed out. Following that they were washed in a jar filled with lacquer thinner then allowed to dry. Next I put the bushings back in the oven just to see if any more crud might run out. It did. More black ooze. Another cleaning with lacquer thinner, then allowed to dry. Next I placed the bushings in a container of lube and put this into the oven at 250F. After several minutes they were removed from the oven and allowed to cool while still submerged in the lube. Next I removed the bushings from the tin filled with lube and then placed them in a disposable pie tin to be baked dry at 250F. No more black ooze. Once more the bushings were put in a container filled with fresh lube and baked at 250F for a few minutes, then removed and allowed to cool. Now they were ready to be installed. the lube being used is 20 wt turbine oil. ( I'm using Texaco R&O 46).
Note the spherical ends. This feature makes possible a limited amount of alignment adjustment between the upper and lower casings once all of the parts are assembled.
Oil reserve felt pads: These I lightly cleaned by soaking/washing in a lacquer thinner bath, then allowed them to dry. This was followed by filling the pads with 20 wt turbine oil to the point where the pads were fully saturated with the lube.
Bearing end cap, thrust pad and ball, after cleaning. The end cap went into the carb cleaner. The ball and pad were simply wiped clean with a paper towel. The bearing ball mic's at 2mm in diameter. The pad measures 1mm thick.
Without the ball. The previously used indented side is now faced down. The unused side provides a flat new surface to engage the thrust ball. I'll try it this way for now. Perhaps, later on, a heavy bronze end cap with a fresh Delrin thrust pad could be made for this! I'll put that idea on the back burner for something to try at a later date. Also, the bearing ball could be replaced with another one of different material.
The lower bushing after a few cleaning and lube cycles. It awaits to be inserted into the spherical socket of the end case. The end cap with thrust pad is positioned to receive using m2.5 x .45 machine screws The larger oil retaining sponge pad is laid against the end case.
The bushing is inserted with its spherical end fitted within the spherical socket of the end case.
The inner cap is partially assembled with the smaller sponge pad and the bronze bush retainer spring. it is ready to be fitted over the bushing end and onto the case.
After fastening the bearing assembly onto the lower case. The inner cap tensions the bushing while allowing the bushing to be rotated a small amount within its spherical socket fitting. The m2.5 hex jam nuts were carefully ,and somewhat tediously, fitted with my fingers to engage the threads of the machine screws. Once the nuts had a 'start' on the threads I used a screw driver to engage the slotted end of the screw while holding the hex nut with a small plier. In this way I was able to tighten the assembled bushing quite firmly to its end case. Do note that the spherical end of the bushing must not be locked into position. It must be able to swivel within its assembly. Test this by placing the rotor shaft in the bushing and manipulate the bushing attitude using the leverage of the rotor shaft. If the bushing puts up too much resistance there is something within the assembly that is wrong.
The bushing assembly is installed to the upper case the same as the lower but with the exception that there is no end cap. The rotor shaft fits through the upper case. Like the lower case, it is important to insure that the upper bushing can be swiveled within its mount.
The importance of the swivel mountings is for aligning the rotor shaft to the bushings. Ideally, upon assembly, the rotor will spin within the upper and lower bushings only touching a film of oil and not making hard contact with any part of the bushings themselves.
Another view of the end cases after cleaning and reassembly of the bushings.
The thrust ball, in my example, is magnetized and sticks itself to the end of the rotor shaft. Very handy for assembly and disassembly. Failing the magnetism, a small dab of grease may be used to retain the 2mm bearing ball into the countersink end of the rotor shaft during assembly.
Above three photos: To assemble the motor I fitted the rotor (with thrust ball stuck within the c-sink at end of the shaft) into the bushing of the lower case. Then the stator core was slipped over, then the upper case. Care was taken to align the wire harness and fit it through the intended port of the upper case. Note the photo showing the position of the posts. these fit up through the cast chassis for mounting and must be oriented as shown.
Btw, the motor in the above photo is not yet fully assembled but is complete enough to make preliminary bushing alignment adjustments.
Before installing the motor to the chassis. And before applying electricity to the motor. With the four assembly bolts not yet tightened, slightly loose. Hold the motor in one hand. With the other hand hold the top of the rotor shaft between thumb and forefinger. Wiggle the shaft back and forth, around and forth, to operate the self aligning bushings within the upper and lower casings in an operation designed to align bushings upper and lower to the rotor shaft. Then, spin the rotor shaft by giving a spin with the thumb/forefinger hand. Observe how long the rotor spins. Repeat this process until the longest spin-down time is achieved. Tighten the four bolts, then double check the spin-down time. If longest spin-down time is achieved after tightening the four bolts, you've got it.
editors note: It has been my experience, after a few years of working on different TD124 players and seeing the variety of conditions that these motors may be found to be in, I have revised my technique for final assembly as follows.....
Noted above in the paragraph prior to this note, it is in the hand-held assembly stage where the most effective method of shaft centering can happen. When the upper and lower case bushings are best aligned, there will be the longest spin-down time. When in good alignment the rotor will free-spin for several seconds before coming to a gradual halt.
You can mimic a dog chasing its tail using the stethoscope method to align then tighten. What the stethoscope will tell you is when you have found the lowest noise level while the motor runs under electrical power. I have found that when I have achieved best alignment in the previous hand-held stage, no amount of tweaking using the stethoscope as a guide will actually improve the bushing-shaft alignment. You already have the optimum shaft/bushing alignment, but you might make it worse.
The factors that affect free-spin times.
Above three photos: using a service jig to hold the motor unit while listening to the running motor with a stethoscope.
It has been the process to allow the motor to run-in for a week of steady use on the turntable and then take the motor off the chassis, disassemble, clean, inspect, re-lube, assemble and adjust all over again. I find this process most beneficial when having replaced the rotor bushings with new ones. And depending on the running clearances allowed by the replacement bushings, there may be something of a break-in process. It is always good to double check your work this way, even if the motor appears to be running optimally. Once the motor has been inspected after a week of run-in, and the repeat process appears to result in excellent operating behavior, it can be expected that the motor will run this way for several years.
Some anecdotal trouble shooting.
There was this one turntable, chassis # 13943 that came to me with a dead motor. I restored it to operating condition after I had replaced the stator coils with a new set from AudioSilente in Rome, Italy. However there were further troubles. The trouble was low power output at the rotor shaft, and I was having trouble identifying the source of it. I finally found the problem to be the blue wire that carries voltage to the one post on the strobe bulb. That one wire, when removed from the harness and looked at closely in good light had deteriorated in various spots along its length. The result was poor current flow to the lamp and thus reducing the amount of volts getting through to the motor. The solution was to replace the wire with one of the same gage but new and undamaged. That solved the problem. Lesson learned was to always inspect all wires for damage/defects in the motor circuits. (Copper hook-up wire is what is needed. Keep the color coding same as the schematic.)
Another thing that can fool you into thinking your motor isn't working right; Motor/bearing lube gets splashed onto the idler wheel and results in loss of traction between the wheel and the driven inner rim of the iron flywheel. The lesson learned is to keep the interior of the chassis under the flywheel spotless clean and free of any oil residue. Pay attention to this detail when applying lube to the main bearing. To clean the oil off of the inner platter I will use either alcohol or acetone. To clean the rubber idler tire I will use lacquer thinner. It is a tad 'hotter' than the acetone and softens the rubber nicely. Don't drink any of this.