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

[Brent Hilpert]

> On 2015-Mar-03, at 11:00 AM, Enrico Lazzerini wrote:
>> Well, on the zener i measured 12,45V. So it is a 12V I think. Not 15V as I
>> previous supposed. It power the pins as I written so :
>> 
>> About powers:
>> LB1612 pin 19 datasheet says 8-14VDC
>> TC1642P pin 16 datasheet says 5-9.5VDC
>> C358C pin 8 datasheet says until +32vdc
>> 
>> I could try to substitute the zener with a 7808 ic 1W.
>> This could keep all is not warm and protect. RIGHT?

Brent wrote:
> 8V of a 7808 may be low/marginal for the 8.5V min specified in the LB1620
> datasheet (at least in the Sanyo one I'm looking at).
> 
> You could add a diode or two in series with the GND leg of the 7808 to raise
> the voltage to around 8.6V (1 diode) or 9.2V (2 diodes).
> (cathode to GND, ordinary 1N400x for example).=
> 

On 2015-Mar-03, at 2:25 PM, Enrico Lazzerini wrote:
> 
> I thought to this with a 7808:
> https://www.dropbox.com/s/ekj0bftrh86nhsa/PowerOK.jpg?dl=0
> to test before to resolder the new LB1620.
> 
> Thanks for the kind support of all of you.
> Enrico

If you cut where you indicate and install the 7808 across that  point, you will miss the supply point for the hall-effect sensors, they would still be supplied by the higher zener V (note R109 that takes off around the R112-D102 junction to head to the sensors).

Rather than cutting the trace, I would just remove R112 & D102 and install the 7808 across the former R112 opening, with the aforementioned diode(s) in the GND leg. There's enough copper there you may be able to drill a new hole or two to catch the 7808 legs.

(Alternatively, 9.1V zeners are pretty common.)