Gordon,

I have millwaki drill same thing happened it works
but at full speed only. I found output transistor
was ok and no PWM. I am sure I can add pic10 to control
it but I do not have time for it. Two things can happen

1. output transistor got shorted
2. PWM chip got damaged

if you hear noise while pressing the button and the noise 
changes it means your PWM is working.

Andre 



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
Of Gordon Williams
Sent: Tuesday, March 06, 2007 9:25 AM
To: pic microcontroller discussion list
Subject: [EE] Cordless Drill Speed Control problem


Hi,

I have a Ryobi cordless drill where the speed control has gone but it still
works at full speed.  I was wondering if anyone has taken something similar
apart and could point me in the right direction.  I've searched the web but
come up blank.

This drill has is about 8 years old but has only seen occasional work.  When
using it yesterday I found that I could no longer control the speed.  It was
either all or nothing.  When I slowly squeeze the trigger I can barely hear
a very high pitch noise (as I usually hear with slow speed operation) but
with no movement from the motor and using my hand I can easily turn the
motor in both directions.  As I squeeze a bit more the drill turns on full
speed.

I was wondering if there was a secondary switch in the trigger that would
by-pass the PWM and FET system and connect the battery directly to the
motor.  The high pitched noise I am assuming is the PWM.

Any ideas on how these things work?

Regards,

Gordon Williams

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