On Mon, 24 Oct 2016 10:15:21 +0100, news wrote:

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.


Looking at the picture, I can't see any signs of a triac (nor any place
on that PCB where one might lie hidden from view unless it's mounted on
the reverse side).

The circled area marked "RV1" looks like this Variable Resistor
component may have been replaced by a couple of resistors located at the
switch (it's hard to tell, but it looks like the mounting holes are wired
back to the switch).

The two electrolytic caps at the opposite end of the board look
suspiciously like they may be a couple of 200vdc rated caps wired in
series to provide a smoothed 350v HT supply for a switching converter
(perhaps there *are* additional surface mount components on the underside
after all but the PCB's appearance suggests otherwise).

Apart from the 6 rectifier diodes and a small glass diode (probably a
zenner), I can see what looks like a 15 ohm (green bodied) resistor with
what looks like a smaller 22K ohm resistor alongside. The 15 ohm resistor
is probably a current inrush limiter for the 350v HT rectifier circuit
and the 22K looks like it feeds current to that glass diode (zenner?).

The remaining components could both be small capacitors. The black one
certainly is but the red "ceramic disk" might be a spike clipping
varistor (although, ime, these are usually coloured blue).

Unfortunately, without a set of decent photos to show both sides of the
PCB *clearly* (the wires should have been moved aside or a better angle
of shot chosen to make it clear as to what and how many wires are
connected to the board), it's impossible to work out exactly how this
functions as a DC motor speed controller and what possible failure mode
could have led to the symptoms and measurements you've taken with your
moving coil multimeter. We can take educated guesses but unless someone
familiar with the innards of a DC05 recognises that board, an educated
guess is the best you're going to get.

If you can't track down a service manual with circuit diagrams for that
model of vacuum cleaner, the wiring will have to traced (both the PCB
circuit and the rest of the wiring including switches and motors etc) to
recreate a circuit diagram in order to continue the quest to effect a
repair.

Unless you can't actually see the switch connections, it might be worth
posting a few more photos (uncluttered views both sides of the board and
a photo or two of the switch wiring). I'm guessing you'll find a couple
of resistors wired directly onto the switch contacts once you gain access
(if you have access to one of those cheap snake (bore-scope) cameras, you
might be able get enough of a view to determine whether or not this is
the case).

http://dysonrepairmanuals.com/DC05%20Folder/DC05%20page.html is a good
starting point of reference which, at a glance, looks quite useful. :-)

However, further googling got me no nearer, as promised in the link
above, to tracking down a service manual or circuit diagram so it looks
like you'll have to trace the circuitry yourself to create a full circuit
diagram along with an accurate parts list. Once you have this, the only
likely proprietary bits will be the switch and the motor. The motor is
apparently readily available (take heed of the advice).

I'm not so sure about the switch - you can google the various spare
parts traders' sites yourself if the switch proves to be the fault. The
fact that the 230vdc motor still runs slowly on a few dozen volts
suggests the problem isn't there (BICBW).

Good luck & HTH

--
Johnny B Good