[TriLUG] cdrom: does pushing the tray in damage them?
davemarcus at pobox.com
Tue Oct 10 04:48:03 EDT 2006
Having observed some further activity on this thread:
This is largely trivia...
I don't know the opening and closing mechanism on current CD devices; so I'll be talking about the previous Sony CD player I had mentioned. This may or may not be of value.
It's been quite a few moons so I don't remember the whole detail of the thing but... There was some cam-ing action that went on at both fully open and fully closed positions of the tray which triggered microswitches to indicate the said positions of the tray. Pushing the door released the open switch and started a close cycle. There was also some logic, apparently, which said hey I've been running the motor to close the door for a while but have not got an all the way closed signal. So open the door back up. This sounds to me like what you've got failing.
In the case of the broken system I had (and I figured this out by taking the thing apart and fixing it...) there was a spring in the cam-ing mechanics which served to hold the cam in position. The anchor post for the fixed end of the spring suffered material fatigue and broke off!!! (Bah! Cheap plastic junk!) I fixed this (temporarily, it broke again ... what can ya do?) by tapping a hole and super-glueing a small machine screw in the place of the broken plastic part.
Manufacturers usually go with limit switch mechanisms rather than a sophisticated feedback and/or sense circuit (as Aaron describes). The switch mechanism is pure digital; the other, quite a bit of analog tom-foolery going on. Yeah, this could work... and would avoid the breakdown involved in using switches... but the circuitry would be fancier, more expensive, and more prone to false signals.
Optical sensors could be used rather than micro switches. They'd be more reliable. But they'd cost $5.00 instead of $1.50... so, this doesn't get done on consumer devices.
Mechanical moving parts are just naughty.
and so it goes...
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