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

Mon Mar 2 07:48:52 CST 2015

Well, i desolder the LB1620... it has obvious signs of burning under
the chips and also on the pcb.

I saw the smoke coming from that place but I thought it came from one
of cap of 2700pf instead came from the chip.

The short circuit between +24vdc and the ground is gone out.

+24vdc go just at pin 4 of the LB1620.

+24vdc to R112 and the D102 Zener that is saved so from here to pins: 19, 2
and 12 of the LB1620 then it continue to pin 16 of the TC9142P.

The datasheet of this last one say that the power voltage would be between
5Vdc and 9,5Vdc. So would this say that the zenere has to be from
5 to 9 vdc? Have i to measure the exact voltage on pin 16 of the TC9142P
without the  LB1620 and how have i to expect?

The LB1620 is smoked. What other components must be tested to ensure
that the new LB1620 can not be broken just fitted?

Thanks a lot.

E.

--------- Original Message --------

 Da: "General Discussion: On-Topic Posts" <cctech at classiccmp.org>

 To: "General Discussion: On-Topic Posts" <cctech at classiccmp.org>

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

 Data: 02/03/15 04:20

 Indeed, pin 4 (Vcc1) should be +24V, this is for the motor windings drive.

 You need to look at pin 19 (Vcc2) of the LB1620 or the voltage across zener
D102.

 Follow the pcb trace from the junction of R112 and D102, goes to pin 19,
looks like pins 9 & 2 as well, and on to supply the other ICs.

 On 2015-Mar-01, at 1:38 PM, Enrico Lazzerini wrote:

 > 

 > Mhmhm... i checked the pcb. The LB1620 pin 4 is wired to the pin on
which I

 > think comes +24vdc... so... let me check what could happens before.
Could

 > happens that is it broken something and it goes to this little pcb
+24vdc

 > instead of 12-15vdc??? 

 > 

 > I misured the voltage coming to this pcb and over there is +24VDC

 > This explain well the why this pcb smoke and it is hot.

 > 

 > 

 > Enrico

 > 

 > -----Messaggio originale-----

 > Da: cctech [mailto:cctech-bounces at classiccmp.org] Per conto di Brent
Hilpert

 > Inviato: domenica 1 marzo 2015 22:08

 > A: General Discussion: On-Topic Posts

 > Oggetto: Re: How to save two Mitsubishi M2896 drive (spindle motor
smoked!)

 > 

 > 

 > On 2015-Mar-01, at 9:56 AM, Enrico Lazzerini wrote:

 > 

 >> 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.

 >> 

 > 

 > I notice in one of the photos you have written 15V for the zener D102,
and

 > on both boards they look like they have been replaced.

 > 

 > D102 and R112 are a simple regulator to reduce the +24V down for the
chip

 > supplies (looking at the photos to trace the circuit).

 > +24 is otherwise used directly only for the motor windings, in part
via Vcc1

 > on the LB1620.

 > 

 > The LB1620 datasheet specifies the Vcc2 range for the 1620 to be only
8.5 to

 > 14V, not 15V.

 > 

 > Check the Vcc2/zener level to see whether the zeners are good and what

 > voltage they are.

 > I expect Vcc2 (and the zener V) is supposed to be 12V or 9V.

 > 

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