Sony TC-164SD servicing notes

[Studio263]

I’ve just finished renovating a Sony TC-164SD portable cassette recorder, this was their top portable model from 1976 until 1981. It replaced the very popular TC-152SD and TC-153SD, and was sold alongside the TC-158SD as a more expensive option for those requiring higher quality recording and playback. This is a lavish, complex machine, it has two motors (including a direct drive one for the capstan), peak reading meters and Dolby B noise reduction. Sony’s ‘F&F’ ferrite head is also used. The chassis is made from aluminium to keep the weight down, although this is largely negated by the 8 ‘D’ sized batteries that are needed to run it. More information here:

http://www.thevintageknob.org/sony-TC-164SD.html

In performance terms it is the equal of Sony’s full sized TC-229SD (and therefore the TC-K7 and TC-K8B as well, which apart from the meters are the same thing). This was the last new Sony portable cassette deck before the TC-D5 range came and killed off just about everything else, that horrible plastic Marantz thing (CP-240? Yuk!) aside.

The greases used in this TC-164SD had all turned to a thick, sticky wax. This affected the operation of the rewind idler, the record switch linkage and the back tension brake pad. Trying to thin this out by adding solvents does not work, it is instead necessary to take each part off and clean it properly. After that I used Castrol LM grease to re-lubricate. None of the bulbs worked either, there are two series strings of 6V / 35mA lamps for the VU meters and for the cassette compartment and tape counter. Replacement is straightforward. The built-in loudspeaker was open circuit; it is a special size and not easily replaced. Carefully removing the sealant from over where the voice coil lead outs run up the inside of the cone showed that the voice coil was OK but there was no continuity between one end of it and the pigtail out to the tags. Some careful soldering sorted that, the repair was then sealed with some epoxy resin.

The remaining fault concerned the DD motor, which sometimes wouldn’t start. Also, there was audible flutter when playing the speed test tape, the tone was stable but had a ‘grating’ character to it. As the speed stability of these machines should be subjectively perfect (just as it is with the TC-D5) there was clearly something amiss. The motor used is a DC brush type, like a smaller version of what they used in the PS-6750 turntable. An FG sensor on the tail shaft provides servo feedback so that the motor ‘locks’ at the correct speed. Needless to say you can’t buy these motors and more, so it was necessary to repair it.

Luckily, it is a high quality motor which with care can be dismantled. First remove the thrust bearing, then the drum for the FG pickup. Heating the area around the grub screws with a soldering iron will help release the sealing paint that these are set in with. After this, the FG coil can be carefully removed by feeding its leadouts back through the hole in the side of the main motor body. Rough handling will break the leadouts away from the winding, so one must above all be very gentle. After that, the lower magnet and polepiece can be removed, exposing the rear bearing plate to the motor itself. This is secured with 3 screws around the edge, do not touch the inner ones which set the phasing of the brushes in relation to the stator core. At this stage I refitted the FG pickup drum (just the metal part, not the coil) to retain the rotor in the backplate of the motor. Removing the pulley for the reel drive at the other end allows the complete rotor and brush assembly to be withdrawn together, thus avoiding the risk of damaging the brushes.

The fault observed can have two causes. The first one is that Sony used foam rubber to pack out the back of the brush springs, and this gets sticky and shrinks with age. If this happens the brushes get pulled out of contact with the armature and the motor works erratically before failing altogether – this is what had happened to this example. Digging out the sticky mess and fitting new pieces of foam (it can be bought in sheets and cut to size) solved the problem. Another thing that can happen is that the carbon blocks become detached from the arched phosphor bronze springs. This is more difficult to resolve, but in the past I’ve solved it using conductive epoxy resin. With everything cleaned and repaired the motor went back together, being very careful not to damage or mark anything of course. The position of the FG drum should be set so that it just avoids fouling the backplate of the motor when the shaft is pushed fully upwards. The thrust bearing can then be set so a small amount of vertical play but not too much – these are portable machines and are expected to work properly even when being swung about.

Note that similar problems affect the motor of the PS-6750 as well, but it is much bigger and easier to deal with. Weak torque, poor stability and a reluctance to start are the usual symptoms.

A test showed that the motor now worked correctly, which was a relief. This really is an excellent recorder, if a bit extravagant perhaps. It is nice to see it working correctly again.