Re: a bit OT:Repairing brushless DC motor?

Just thinking aloud, the following may or may not be relevant ....

1. I can see 2 off TIP137 which are PNP darlington, are the other
two also TIP 137, or the complementary NPN TIP 132? (I'm
assuming that for a brushless DC motor, the field coils will be
commutated by an H bridge)

2. Is it a Stepper motor, which might also be suggested by the
number of leads?

3. You mention corrosion; my experience is that many electronic faults can
be cured by touching all joints with a soldering iron, to resolve dry
joints.

4. If one of the power darlingtons was short circuit and holding the field
coil
in one polarity, or open circuit, and not permitting the dirction of the
field to
change, this might produce the effect you describe.

5. Look at the collector voltage of each power transistor, this might give
you
a first indication of the state of the field driving .

6. This is a bit like a GP diagnosing your illness by you describing over
the
phone the colour of your urine :-)


"Tim" <duttondock@xxxxxxxxxx> wrote in message
news:3e994eb6-69b7-4834-b52c-01a3a50050e7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
A customer has a failed 24V heating circ pump on his boat. It's based
on a standard domestic ('Grundfos type') central heating pump. The
mains motor has been changed for a (presumably) brushless DC motor
He's enquired about getting it repaired, and has had answers varying
between 'No' and 'We can sell you a new pump for £500'.

The spindle turns freely with the power off, putting on the power
holds it in one position.

Here are some pics of the electronics, looks pretty basic. To my
untutored (read 'behind the times'!) eye appears to be four small
power transistors, six smaller transistors(?) and a few standard
resistors & capacitors. There are three sets of leads going from
control board and disappearing into the motor case apart from the red
& black pair (power in). Five leads which look to be the main motor
leads. Six smaller leads which I'm guessing must come from a tacho/
encoder. Three small leads, maybe speed control pot.

Pics of the innards:-

http://i559.photobucket.com/albums/ss38/Timleech_2009/DSCF2546.jpg

http://i559.photobucket.com/albums/ss38/Timleech_2009/DSCF2548.jpg

http://i559.photobucket.com/albums/ss38/Timleech_2009/DSCF2553.jpg

I'm looking for suggestions as to what checks I could make to track
down faulty components, also is there a more or less 'standard'
circuit for this sort of controller? If the motor windings are OK I
reckon it should be within my capabilities to repair the circuit board
as it's all discrete components. Nothing is obviously cooked, there's
a little bit of corrosion on the PCB tracks.
I have decent multimeters and even an old oscilloscope hanging on the
wall, not been used for a while but probably still works.
Alternatively, a pointer to someone who could repair for sensible
money, preferably in the NW, would be useful.

Thanks for any help
Tim


.

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