On Sat, 22 Oct 2016 19:29:20 GMT, Johnny B Good
wrote:



There's a good chance that the switch feeds the power to a bridge
rectifier in positions 3 & 4. Using a 2 pole 4 way switch will allow one
of the brush head motor wires to be transferred from a DC output terminal
(+ve or -ve) on the rectifier to one of its ac input terminals (~),
effectively turning the circuit into a half-wave rectifier cutting the
unsmoothed averaged DC voltage in half[1]. It's a cheap and crude (but
effective) form of DC motor speed control.

The problem could be a switch or rectifier fault or just simply a broken
or disconnected wire between the switch and the brush head motor circuit.
You'll have to gain access to the switch wiring if you want to pursue
this fault finding exercise any further.


Picture of PCB in the handle adjacent to the switch here

http://tinypic.com/view.php?pic=15xq...9#.WA3QG12CixF

The diodes seem to check out with .75V forward voltage and no reverse
current.

It seems to have a triac in the circuit, I cannot get the switch out
to see where the wires go.

AJH