Fixing trace on a motor PCB

Thread Starter

Sam Matthews

Joined Jan 16, 2016
178
I have a motor board out of a dyson vacuum hoover that controls the brush motor in the head, which is a 240VDC motor. The board is powered via 240VAC and converts through the typical bridge rectification method of 4 diodes. It appears to have a 400v 100uF capacitor to smooth this rectified voltage out. My issue is that there is a broken trace between a small capacitor and a resistor, and this is causing my motor not to work.

The question i'm asking is; is it safe to solder a wire to bridge this breakage?

I have had the board unplugged for 24hours, how long would you say this capacitor would take to discharge, or would it not need to discharge for it to be safe to bridge this break with a soldered wire?
 

dl324

Joined Mar 30, 2015
16,845
Just make sure the wire is sized to handle the current.

To be safe, short the cap terminals to move sure it's discharged.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Normally if you scrape clean any PCCT board protection down to the solder or copper of the trace and tin it and solder a copper wire bridge on each trace.
If unsure of any capacitor, just short it with the power off, but 24hrs seems a reasonable time for a small cap to self discharge.
Are you sure that is not the Chinese knock-off version, DieSoon?:)

Max.
 

#12

Joined Nov 30, 2010
18,224
Bridging burnt circuit board traces is a necessary skill, not an uncertain kludge with unpredictable results. It's just a tool that every technician is supposed to know.
 

Thread Starter

Sam Matthews

Joined Jan 16, 2016
178
So if i just short the cap out, with a wire or with a resistor?

The trace thats broken is very thin, however i will use something substantial to handle the current from the 240v motor.

I know this is some basic principles but i just wanted to double check i was safe to put the soldering iron to the copper with this capacitor on board after AC power.
 

debe

Joined Sep 21, 2010
1,389
Max, you will find Dyson shifted manufacturing to China quite some time ago ( cheep labour but still an expensive product)
 

dl324

Joined Mar 30, 2015
16,845
Dyson shifted manufacturing to China quite some time ago ( cheep labour but still an expensive product)
That's unfortunate. I bought one about ten years ago and it still works well. Prior to that, I was buying a new vacuum every few years because they weren't cost effective to repair.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Yes, but by this time a 100μf it should be fully discharged!
And that value is not very large if it were for smoothing a motor supply.
Is it a P.M. motor, BTW?
Max.
 

dl324

Joined Mar 30, 2015
16,845
I, for some reason, didn't expect this to happen and it scared the living day lights out of me.
When I was in college, some jokers liked to charge caps and put them back in the storage drawers hoping to zap some unsuspecting classmate or instructor... But they weren't working with high voltages.
 

Thread Starter

Sam Matthews

Joined Jan 16, 2016
178
The lead is burnt and the cap lead has a little chunk missing >.< - So, back to the fault at hand. It seems the break in the pcb was not the issue after all...

I'm attempting to repair a AC/DC Motor board. What confuses me here though is that the board holds a MCU. Why on earth would such a board have a MCU on there? The board doesn't need to do any switching from my knowledge, the switching is done elsewhere on the vacuum hoover.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
If the motor controls the rollers etc, are they are variable speed?
You did not mention the original symptom, if the motor does not turn, try it on a low voltage supply, it does not appear very large, as a last resort, try an automotive battery, it should run around 100rpm at least.
Can you post a pic of the board?
Max.
 

Thread Starter

Sam Matthews

Joined Jan 16, 2016
178
I doubt its a variable speed enabled if i'm honest. But i'm more than likely incorrect.

I will attempt attaching this motor to a 12v source, thats as high as i have though. Not sure if it will spin.

image.jpg image.jpg
 
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