Memorex 102 20MB Hard disk - Found It!

Well, it _may_ be... I've had another look at the manual on Bitsavers. There's a clock track on the bottom platter with a fixed head (as you say). This seems ot be used as the feedback of the motor speed control, it also can be divided down to produce the sector pulse or a bit clock. Of course the controller doesn't have to use that signal. Unfortuately much of this circuitry seems to be in one of the gate arrays. This will make it difficult to debug and even more diffuclt to repair. I hope that's not the problem. But I woul still check it. See if tyhe motor speed feedback signal looks sensible too while you're in there.. And also, of course ,look at the read data signal. Does it look senesible? Could this be a controller problem? Do you know whether either the controller of drive are definitely OK? -tony