Sony HMK-70 TTS360 turntable spindle problem

[ronbryan]

I am hoping that someone is familiar with this Sony HMK-70 cassette/disc/radio system. The turntable is a belt-drive Sony TTS360, which has a problem.

The turntable would not rotate. This was initially because the belt was not engaged and the spindle bearing was seized due to old grease. When the spindle bearing and spindle were cleaned, greased and replaced, the spindle was about 5mm too low in the bearing and the cam and spindle gear would not engage with the return pawl and large gear.

There was no sign of a thrust pad in the bottom of the bearing, which was open-ended. There was just a set screw in the side of the bearing that engaged in a broad register turned on the spindle to prevent the spindle from pulling out when removing the turntable from the taper. The spindle has a small hemisphere turned in the bottom (see photo), which I assume should bear against something to take the thrust of the turntable.

When a temporary 4mm thick washer was placed between the spindle gear and the top of the bearing fixing nut, lining up the cam with the return pawl etc, the turntable spun properly and the mechanism returned the pickup to the rest as it should.

Does anyone know what part is missing, or how the correct spindle height is set and the thrust is transferred from the spindle to the bearing?

Ron

[BRASSBITS]

you need a thrust pad with a concave for the ball at the bottom of the spindle to run in.
the original one was some sort of rubber

[ronbryan]

I have just noticed there is a small circlip about 2mm inside the lower end of the bearing, some distance from the shaft end. That must have retained the thrust pad

Ron

[ronbryan]

If the thrust pad is to be hard rubber, should that be synthetic, such as neoprene or natural as can be found in some erasers. I do not know if natural rubber will withstand the grease and oil that lubricates the spindle bearing. Does anyone have suggestions?

The alternative to a rubber thrust pad would be a bronze or nylon bush. Just how much extra rumble that would make remains to be seen.

Ron

Ron

[BRASSBITS]

have you got the service manual it will show an exploded view of it

[ronbryan]

The exploded view I have found in the manual only shows the bearing as an assembly, part X-48274-08-0. No view of the internal parts, e.g. thrust block or circlip is provided. See the bottom centre of the drawing attached.

Do you have a detailed view of the bearing parts?

Ron

[Michael Maurice]

I have repaired these in the past using M4 washers and a steel ball. The other way is to use an M8 nylon bolt with a steel ball in the centre.

[ronbryan]

Thanks Brassbits and Michael for the advice. I've made some progress with the missing thrust bearing problem, so the details are here if anyone else has the same problem.

The diameter of the turntable spindle is 0.275", almost 7mm. I considered cutting a 7mm cross-section nitrile 'O' ring to make the thrust pad, but the online supplier I looked at had a minimum order of £10. I also considered a natural hard rubber eraser,, but I have always had problems cutting rubber cleanly as it likes to move away from the cutter given half a chance and the only cylindrical eraser I could find was 10mm diameter.

The solution I used was Michael's suggestion. I found that the slim 3mm steel flat washers I had were a close fit in the bearing, so I fitted two of those against the circlip and rested a 3/16" steel ball bearing on the 3mm hole in the washers. With the shaft button running on the ball bearing, it raised the shaft cam to the correct height with respect to the return pawl. The shaft pinion and large return gear also meshed properly. The shaft and thrust bearing was lubricated with white grease, which was all I had.

One of the soft motor support rubbers (the red one) had partially perished, but I managed to pack it with a squashy rubber grommet to make the motor shaft vertical when pulled by the drive belt.

The 0.8uF 250V AC capacitor in series with one of the two 100V motor windings was replaced as it was leaking and getting hot. There was just room (and spare holes in the pcb) to fit 2 x 0.47uF 1000V polycarbonate capacitors.

The new thrust bearing was found to work well, with the turntable running silently. The belt change, pickup return and reject functions also worked correctly. The 33/45 turntable speeds were checked as ok with a strobe disc.

Ron