this is easily fixable, but as noted above, you do have to remove the the bottom which is quite a few screws. i think technics updated the design on this as neither my 1210MK2s or 1210M3D have this problem. what is happening is that the bottom of the shaft has a C clip on it that holds the white plastic actuator, the spring and the ball bearing in place when it's all together. the shaft and the knob are supposed to never be separated from each other and when they are, the shaft is allowed to drop down allowing the power switch to basically fall apart. on my decks there is a C clip at both the bottom and the top of the shaft so that even when the power knob is removed, the shaft remains where it is. you've got lots of options as to what to do. you can:
1. pay big bucks to repair place only to have it happen again
2. get updated parts and pay big bucks to said repair place to have it fixed for good
3. take the deck apart yourself and fix it and be sure to super glue the knob to the shaft
4 buy the updated part and fix it yourself
5 fix it yourself and update to M3D style knob (my personal favorite)
i think i have some pics if you want to do it yourself. this is also discussed in the "technics 1200 FAQ" that is on various pages throughout the internet. this is not very difficult to do, i just don't want to go into great detail on how to do it if you're gonna go to a repair place anyway. hth - jeff h