On Wed, 02 Nov 2016 10:09:33 +0000, news wrote:
On Tue, 25 Oct 2016 02:31:50 GMT, Johnny B Good
wrote:
On Tue, 25 Oct 2016 00:00:18 +0100, news wrote:
On Mon, 24 Oct 2016 11:18:20 GMT, Johnny B Good
wrote:
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 black rectangle with a heat sink in the side above C2, what is
it?
I can't see any evidence of a heatsink from that angle. However, it's
possible that what I thought was a small 100nF capacitor might well be a
plastic power transistor or triac with the heatsink tab chopped off
flush to the encapsulation.
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component may have been replaced by a couple of resistors located at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).
RV1 is the red blob
Ok, now you've given me another clue, I can see how that would fit. The
red blob, which I have to assume is a varistor in spite of it not being
blue, looks like it has been flipped up from its intended laid down flat
mounting position as implied by the silk screen print.
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)
Yes I thought it was a zener too.
I will get some better photos up and see if I can trace the circuit
and also the other PCB in the motorhead but as I only want the brush
to work would there be any harm in abandoning the Dyson PCB and
feeding it with a simple 400V rated bridge rectifier off a separate
switch?
Assuming that the "100nF capacitor" is actually a triac, I doubt you'll
get away with just a simple bridge rectifier. However, if you're going
to experiment, that 400v rating should be for the ac input voltage based
on the assumption that the output will be connected to a simple
reservoir smoothing capacitor ripple filter.
The rule of thumb in this case is to rate the diode PIV at 3 times the
maximum rms input voltage since each diode element in the rectifier
bridge will be subjected to twice the peak inverse voltage (1.414 times
the rms ac voltage) due to the peak voltage stored by the smoothing
capacitor. Assuming a perfect sine wave form on a 240v ac supply, each
diode will be subjected to a PIV of 2.828 * 240 volts, just under 680
volts! With an rms voltage at its upper 265v limit, the PIV will be a
whisker under 750 volts.
However, the Public Supply Utility voltage is far from a perfect sine
wave, typically looking like a slightly flat topped sine wave which will
reduce the theoretically calculated peak voltages by a few percent.
Even so, it's always best to use an even higher voltage rating, in this
case 800v PIV, to allow for spike voltages and sub station voltage
controller faults that allow the PSU to go above the 265v rms limit
(unless, of course you deliberately choose a 700 PIV rated diode to
protect the expensive HT switching transistors against such over-volting
events in an act of self sacrifice to blast the safety fuse to
smithereens - diodes and fuses are a damn sight cheaper and easier to
replace than HT switching transistors!).
Good luck & HTH
Yes you have been very helpful, thanks
The gratitude is appreciated. :-)
If you do decide to post any more pictures, try and compose the shots
so
as to maximise clarity. Provide two or more angles of view, bending any
wires aside if necessary and pay attention to the lighting which can
make a huge difference to the clarity of the images.
Digital photography allows anyone to take as many photos as they fancy
of such a "Still Life" subject as this. You can easily fire off half a
dozen or more at various angles and lighting conditions from which to
pick out the best two or three to post up on a web site for us all to
peruse and admire.
Oh, and just one final point. As far as I can make out, there's no
signs
of obvious component damage on that little PCB but, of course triacs and
diodes can develop faults without any obvious signs of failure. However,
when we're dealing with circuits carrying mains voltages, any such
internal failures tend to result in physical damage, either co-lateral
or self inflicted since the most likely failure mode tends not to be a
fail safe open circuit state but rather a dramatic pyrotechnical short
circuiting event.
If as you surmise, there's a triac on the circuit board, it must be
controlled from the switch using a couple of resistors to control the
triggering delay. Such resistors are typically high value resistors of a
low wattage rating. If they've been soldered straight onto the switch
contacts, it's possible they may have been damaged by the action of the
switch sending shockwaves into the contact tags. If the resistors have
been soldered to those contacts via very short leads, they may well have
failed as a result of the accumulated cycles of use over the years. IOW,
don't ignore such components which must exist somewhere external to that
PCB.
I've returned to this after a short break.
I looked at the circuit board by the switch again and realised it is
likely to be a speed control for the brush in the Zorb (rotating no
vacuum) position, so irrelevant to the problem.
http://oi63.tinypic.com/r0ttp5.jpg
Is a picture of what I now think is the power supply to the motor in
the head. The power comes in from the left and out to the motor at the
bottom. The LED is cropped but at the top. It seems to have an
integrated full wave rectifier, some inductances for smoothing and
capacitors plus an unidentified black blob
If the black blob you're referring to is what looks like a disk mounted
on edge to the board, that's most likely a VDR to trim any transient
voltage spikes.
I see the rectifier module (W08M) of which two of its diode elements
form a second fullwave rectifier in conjunction with the two back to back
discrete diodes on the left which act as an additional positive output
terminal feeding one of the two 33K ohm 1W resistors used as a DC ballast
to feed that red LED with ca 5mA of current.
The white oblong component at the bottom is obviously a high voltage
capacitor across the motor terminals and this, in conjunction with the
two inductors forms an RFI filter to suppress interference produced by
the motor's brush gear.
The 2.7Mohm 1/2W resistor (RHS - possibly 2.0Mohm if that dark purple
band is actually black) is effectively wired across the 400vdc rated
smoothing cap at the top to act as a safety discharge resistor in the
event of the circuit having been energised with the motor disconnected or
open circuit just prior to being handled.
When I apply 230V directly to the power in the LED glows red and the
motor does not run.
In which case, it looks like that rectifier module (W08M) must have gone
faulty[1]. The inductors are the only components in series with the motor
supply and they both look to be in robust full health (they should each
show a short circuit reading when tested on the resistance measuring
scale of a DMM or MM (mains disconnected!). I'm assuming that the motor
is still in full working order as your OP suggested (turning slowly with
a few tens of volts applied - hopefully, slowly and *steadily*)
I have also checked the switch and I think some contacts have burned out
but that doesn't account for the fact that the motor won't run when 230V
is applied to the board directly.
http://oi64.tinypic.com/35au4ug.jpg the underside of the board
That picture would have been more useful if you had created a mirror
image (post processed in the GIMP or Photoshop) or had simply used a
mirror to take the photo in the first place!
[1] The only fault I can think of that would still allow the LED to light
up (the difference between full and half brightness can be difficult to
distinguish by memory alone) would require that both positive diode
elements to go open circuit in the bridge rectifier module (W08M).
HTH
--
Johnny B Good