On Mar 1, 10:59 am, "visionset" wrote:
"Matty F" wrote in message

Clip an analogue multimeter to the brush holders and measure the
voltage when it's running, taking due care to not electrocute
yourself.
I doubt that a digital meter will show a fast variation like that.

Okay I'll have to try it with my digital - it's all I have. But the stop
start problem is ~1 second cycle so should be able to observe a change in
reading.

If the voltage goes up and down then the problem must be in the wiring
to the brush holders.

Can you explain why the conclusion - my electronics is a very rusty.

I assume that it's a 230v (thereabouts) AC vacuum cleaner, so there
should be a continuous 230v AC at the brush holders when it's running.
My cheap digital multimeter samples about once per second so that
would be no good to see the problem. Maybe you could use a 230v light
to check the voltage at the brush holders. But you need to be careful
about electric shock so don't be touching anything when the power is
on.
Another possibility is that the commutator is not perfectly round.
That would make the brushes jump up and down when the motor runs fast.
Or (but unlikely) if the whole armature is sliding backwards or
forwards in the end bearings when the motor is running.