The switches on those decks which I have worked on almost my entire professional life do not fail all that often. Being I was a Teac Lead Technician in Chicago I only had to change one Microswitch in the 47 years I have worked on these and I can tell you it was no fun. I have a better idea of how to work on them now with some tricks learned along the years. The most common issue with no functions is due to Dummy plug being out or the wrong one. Check with DVM on ohm or diode test the pin 1 and 11 short no others.
Second the next most common this is the right tension arm. Does it go below 3 o'clock? If it does the the stop is broken and often when that happen by a hit of some kind it can break the microswitches attached to the cam drum the arm is attached to. The current Microswitch is called VX51A2 from Omron and Mouser and Digikey usually have them. They are not regular switches but 50g pressure switches. If the two above are out then try Newark or farnell depending on your country location.
Another cause is that the Pinch Roller linkage is sticky due to bad grease- we used to call it Fish Eye grease as most things in Japan were obtained in some way from Fish. In any event, the linkage is taken apart and the old grease cleaned out and I use Lubriplate 105 to regrease. In all the years I have worked on these a Lubriplate 105 grease linkage has never come in a second time.
Want to know a secret? Oil the capstan bearing by removing the shaft and putting 7-9 drops of AMSoil Signature synthetic oil in the bearing and on shaft as well as down motor shafts- the oil tube take too long as they have decayed foam in them. I take the motor off clean the motor pulley with brasso not sandpaper and then oil the motor with front shaft sticking up and then the back shaft sticking up (Fan will need to come off). If you do this you are likely to get better wow and flutter figures than when it was new as this oil is superior to any I have tested in the last years- I use it exclusively and get wow and flutter from BR20 at .0135%, A2000R= .02% and X1000R= .023%. Not all machines respond the same it all depends on wear and other factors. The oil weight is 0 W30 that I use.
The power supply should be recapped on this unit as a minimum- I do them all the time as a start. It has been a long time since 1978 for caps.