On Wed, 02 Nov 2016 19:57:06 GMT, Johnny B Good
wrote:
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.
It says bTh 100 on it, a search suggests it may be a varistor.
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.
I have checked the forward voltages and the integrated full wave
rectifier is okay. I thought the other two diodes just rectified the
supply for a voltage divider that triggered the LED, I think the LED
has two colours, red (at present) and green when working normally.
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.
Yes I see this.
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.
I see the resistor as brown black green gold, 1 M Ohm but I see what
you say about a discharge resistor
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*)
It turns steadily with 12V and actually runs up fine with 230V ac but
I think the above circuit is sensing something wrong with it and
somehow inhibiting its supply.
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).
I think this is not the case and that the LED in fact contains red and
green elements but not a clue what switches them.
I'm going boss eyed trying to draw the circuit which I can upload if
it would help in further diagnosis?
AJH