If you smell or see smoke from your drive, of course turn it off quickly. OK, where did it come from? Look at all the tiny electrolytic capacitors (known in the trade as Tantalum) to see if any are burned. When new, they are orange or dark blue in color and shaped like a teardrop. Those capacitors have a history of catastrophic failure and can pop like a firecracker or just make a
lot of smoke when they fail. I've seen them short out and drag the +12V line down so the motors didn't work. The regulator IC's have an internal protective feature called "fold-back current limiting, so they will not immediately burn out from an overload like that but the regulator and its supply rectifier will get very hot quickly. If the +12V line is lower than normal, suspect a shorted C15, a 10uF 25V tantalum capacitor on the front of the board.
Another odd failure I've seen is the spindle motor turning all the time, but the drive still works perfectly. The cause is a bad UD2, IC number 7407 or 7417 (those are interchangeable parts). When just part of that IC fails, it keeps the spindle motor running, but with no other symptoms... strange as it seems. You have to listen closely to hear it, especially with no disk inserted.
-- Ray Carlsen --
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