How to save two Mitsubishi M2896 drive (spindle motor smoked!)

[tony duell]

> 
> I have a couple of 8" drives Mitsubishi M2863 slim type that I recovered I
> think around on 1990 both in excellent conditions with which I created
> images and written several floppy disks 8". For some reason, including my
> incompetence, both their spindle motor do not run any more. And powering

OK, what did you do? Seriously, it may help in finding what needs to be replaced.

> correctly with only +24Vdc the circuit part of the engine rotation control
> of the disk (called spindle motor) begins to smoke near a chip LB1620. The
> schematic contained in the maintenance manual of the drive includes
> components of other different model of spindle motor circuit. If that were
> possible, how could I to be able to run the drives correctly: reusing partly
> engine or even replacing it with analogous maybe even creating handcrafted a
> motor with pieces of recovery and manage the number of RPM (I think 360rpm
> for 8" drive) possibly with special circuit ?

Is there a good reason for not restoring this spindle motor to its original
form? The TC9142 chip is a well-known motor speed controller PLL thing, 
if it's the one I am thinking of it has a pin called 33/45 which indicates where
it was intended to be used :-) I've come across it in disk spindle motors,
laser printers (the Canon CX uses them for main and scanner motor control, etc).

The LB1620 looks to be the motor commutation IC. It takes in signals from 3 (I guess)
hall effect sensors, these are just visible, I think, in the track-side PCB photos. The 
IC then drives the 3-phase motor windings, most of the time they are star connected.

You can get data sheets on both these ICs from http://www.datasheetarchive.com

The motor PCB seems to have a 3 pin connector on it, I would guess +24V, ground
and motor_run. I should therefore be easily possible to run it on its own for
testing. I think the first thing you need to do is find that short. The LB1620 is possibly
at fault here, maybe desolder it and see if the short goes away.

-tony