RD54 Stopped Spinning

Jon Elson elson at pico-systems.com
Sat Apr 4 16:17:59 CDT 2015

On 04/04/2015 04:06 PM, Robert Jarratt wrote:
> So when I fired it up again with the scope, the disk 
> started to spin. This was a stroke of luck as I was able 
> to probe what I believe were the outputs of the hall 
> sensors. All three oscillated, but one of them showed 
> significant sideways wobble on the scope, which suggests 
> to me that the signal is not absolutely regular. It does 
> seem to suggest that one of the sensors is not working 
> well. However, would this be enough to explain why it 
> stopped dead in its tracks when it was working before?
Yes, the logic is generally that you decode 6 legal states 
of the Hall sensors to decide which of the 3 motor terminals 
to drive high and low.  if the Hall sensors give a signal 
that has all 3 high, or all 3 low, the decode logic will 
fail, generally leaving all transistors off.  If it gets in 
that state again, a vigorous twist of the drive around the 
spindle axis might shift the rotor to a position where it 
will start up again.
> Changing one of these sensors is probably going to be 
> beyond me :-( Thanks Rob 
I'd get the data off it quickly and retire the drive.  You 
may only have a few minutes run time before the sensors go 
more flaky and the drive shuts off.  But, now that you know 
the secret, you ought to be able to recover data, if that is 
the plan.

Anyway, it seems you have completely diagnosed the problem.


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