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

[Enrico Lazzerini]

Well the verifications taken here:

- Observe (C358)pin7 while alternating the 0/+5 test voltage on the 3rd
connector pin, pin 7 should change accordingly to 0V & 9V. => NO it remain
statically at 7,76V

- Similarly (LB1620)pin11 should be changing. => NO it remain at 3,44V

- The hall sensors may still be suspect. They are supplied by being stacked
in series with two resistors, one each in the ground leg side and +9V supply
side. First thing to do would be to measure the V on the two supply pins of
each hall sensor (the pins closer to the motor center).  The supply voltage
should divided between the 3 sensors and 2 resistors. 
=> The chain is :
- from the +5vdc to R109 = 6,76V
- then from R109 to the 1st hall sensor = 5,17V
- then from the 1st hall sensor to the 2nd hall sensor = 3,62V
- then from the 3rd hall sensor / R110 to the gnd = 2,2v
So at each hall sensor we have (potential difference):
1st = 1.59V
2nd = 1.55v
3rd = 1.42v


The halls sensors feed the LB1620 with a differential drive from each sensor
to avoid having to make a fixed GND reference, which allowed them to be
stacked in series for the supply. In theory you would be able to observe a
change on one of the drive pair of each sensor with the scope as you
manually rotate the rotor but the change may be too small to observe within
the bias from the stacked supply. Properly one would use two scope channels
in A-B difference mode to observe the drive pair.
=> confirm that rotating the motor my voltmeter change a bit its measured
value


- Instead, or in addition, you might try watching the (LB1620)pins1,2,3
outputs while spinning the rotor manually to see if they change.
=> confirm that rotating the motor my voltmeter change a bit its measured
value

Could at this point the problem to be on c358c or the transistor q101?
Enrico