On Sat, 22 Oct 2016 01:34:05 GMT, Johnny B Good
wrote:

From your description, my inference is that the PCB in question is in
the vacuum cleaner itself rather than in the motor head.

No the PCB is actually in the head, it seems to be supplied with DC
via a 4 position switch in the handle which I have not been able to
open up to investigate. The first position is all off, the second is
vacuum only , the third is vacuum and motor head brush which gives a
red light on the motor head PCB and the fourth is supposed to just
rotate the head slowly. I took one input terminal off the PCB (and
broke the push on crimp in doing so) and tested the voltage in
positions 3 and 4. Three powers up the main vacuum motor and supplies
only a few tens of VDC, 4 gives about 90VDC, this suggests a problem
in the switch.






If you repeat
your test with your moving coil multimeter using a suitable AC voltage
range (say 5 to 6 hundred volt scale) and take readings with the test
probes applied each way around, you should see only a very low reverse
reading when applied the wrong way round and an ac voltage reading close
to *double* the expected mains voltage when the rectifier is working as a
fullwave rectifier[1]. If the rectifier has an open circuit diode as your
voltage reading suggests, it will be acting as a halfwave rectifier and
the meter will then read just slightly less than the AC voltage feeding
the rectifier[2].

As you say it reads over 200V on an AC scale with terminals one way
and zero the other.

Looking at the forum Mike suggested the is a common problem with this
switch but no power supply components are mentioned.

I just need to get it apart and look.

AJH