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

[Enrico Lazzerini]

Thanks Tony for your suggestions. What I means is:

It happen in two distinct times every time when I used the drive to read
through a PC with the software IMD to create images of floppy disks 8 ". Not
having the correct power connectors i power the drives in this way: + 5vdc
and ground coming by a PC power supply and +24vdc and ground from a Chinese
power supply. I must have certainly reversed this last one even for a few
seconds exchange +24vdc with the ground. Now both spindle motor supplied
also with only +24vdc start smoking in the vicinity of the chip LB1620 and
cause of cooling you can not touch it as hot it is. If I try to measure the
resistance between pins  +24vdc and ground of each spindle motor drive i get
1327ohm on FD0 while i measure 19ohm on the spindle motor drive FD1. There
are no visible damage nor to the components nor the PCB wires. 
In both pcbs anyway the chips LB1620 sunburnt from not being able to keep a
finger on it. 
I searched on ebay and the only place that has LB1620 seems to be:
http://www.ebay.it/itm/LB1620-INTEGRATED-CIRCUIT-IC-BOX-74-/390955452872?pt=
LH_DefaultDomain_0&hash=item5b06c2c9c8

The input's pins of the pcb are : +24vdc, ground, and the rest could be a
control.

The point is that I have no experience on these components. 
Replace the chip could make it burn again for my inexperience.

Enrico



-----Messaggio originale-----
Da: cctech [mailto:cctech-bounces at classiccmp.org] Per conto di tony duell
Inviato: domenica 1 marzo 2015 17:42
A: General Discussion: On-Topic Posts
Oggetto: RE: How to save two Mitsubishi M2896 drive (spindle motor smoked!)

> 
> 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

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