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Electric Mower repair

2Peter2

May 4, 2018
4
Joined
May 4, 2018
Messages
4
Hi there,

I'm trying to repair my parents mower - a 'Sovereign 24V Lithium-Ion Cordless Rotary Mower'.
It's only two years old, and hasn't had that much use - It packed in last week, having had no problems before.
I only have a basic understanding of electronics, but I'm keen to learn more ... I love repairing things, so thought I'd give this a try.

Here's the rundown so far -

There are no blockages obstructing the blade.

If I press the handle/button start mechanism, the blade occasionally starts up, only to die a second or so later.
Most of the time it doesn't spin, and I only hear a click sound.
When I look 'under the hood', I can see a red light flashing on the circuit board (bottom left corner of circuit board in photo). Also, I can see two points of rust (or is it where it's blown?) - one on the coil(?) wire, and the other on one of the integrated circuit pins (?) ... sorry if those are completely the wrongs terms, I'm new to this!
I'm pretty sure the damage has been done by water seeping into the body, when the blade has been cleaned by the hose pipe!


If anybody can give me a pointer in the right direction, I be most grateful.

Thanks.
 

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Robert_fay

Jun 15, 2017
124
Joined
Jun 15, 2017
Messages
124
Have you looked in the manual for troubleshooting. Some of these the blinking light will tell you the issue. i.e. 3 blinks means this or 4 blinks means this. Maybe not for this, however generally a blinking red led is telling you something.

If not is sounds like there is a safety switch that tells you are still holding the handle that may have a bad or loose connection. I would start going through that portion of the circuit.
 

73's de Edd

Aug 21, 2015
3,658
Joined
Aug 21, 2015
Messages
3,658
Sir 2Peter2 . . . . .

By observation . . . I can only make these guesstimations.
Soooooooo . . .those 9 wire leads only stick up there and are not connected ? Definite copper sulfate deposits near the far right end leads from the copper erosion.
Those most possibly being test points for service analysis.

One can see the heat sink and power control semiconductors, for motor speed control, at the rear.

By virtue of the proximity of the heavy RED wire to the principal 3300 ufd electrolytic capacitor and the closest nearby BROWN, lead . . . . .seems like they would be going to the Li -Ion battery pack, while the heavy BLACK-YELLOW-BLUE wires seem to relate to being connected to the mower motor.

Which I would want be checking as the first thing, to see if it rotates freely or has locked down or has something wrapped around the shaft. Thus accounting for the shut down after initial power up.

Two visible wires are left unaccounted for :

The medium BLACK wire going to a wierd black connector.
And then there is the smaller white wire pair , which justify an RFI choke . . .so it could be the wire pair that goes to the units charger.

Still needed accounting for is the wiring that turns the unit on and speed control . . .if any.

The forthcoming BAAAAAAAAD news . . . . . . that is being a poured / hard potted module that stops all analysis by observation, excluding replacing any accessible bad power semiconductors on the heat sink.

What say ye . . . . .

73's de Edd
.....
 

shrtrnd

Jan 15, 2010
3,876
Joined
Jan 15, 2010
Messages
3,876
73's de Edd is one of the best failure analysis people I've seen on this site.
He's probably got troubleshooting information that will help you out.
I think you're probably right about water causing your problem.
My input, is that the last two electric mowers I've fixed, the switch itself has been the problem.
If you haven't already, I'd open the switch box that engages the mower motor and look inside of it.
Corroded contacts, broken plastic gear or lever parts; just to be sure that when you close the switch,
you're actually getting continuous power to the mower motor.
That's the first thing I'd check anyway.
Good luck.
 

2Peter2

May 4, 2018
4
Joined
May 4, 2018
Messages
4
Have you looked in the manual for troubleshooting. Some of these the blinking light will tell you the issue. i.e. 3 blinks means this or 4 blinks means this. Maybe not for this, however generally a blinking red led is telling you something.

If not is sounds like there is a safety switch that tells you are still holding the handle that may have a bad or loose connection. I would start going through that portion of the circuit.
Sir 2Peter2 . . . . .

By observation . . . I can only make these guesstimations.
Soooooooo . . .those 9 wire leads only stick up there and are not connected ? Definite copper sulfate deposits near the far right end leads from the copper erosion.
Those most possibly being test points for service analysis.

One can see the heat sink and power control semiconductors, for motor speed control, at the rear.

By virtue of the proximity of the heavy RED wire to the principal 3300 ufd electrolytic capacitor and the closest nearby BROWN, lead . . . . .seems like they would be going to the Li -Ion battery pack, while the heavy BLACK-YELLOW-BLUE wires seem to relate to being connected to the mower motor.

Which I would want be checking as the first thing, to see if it rotates freely or has locked down or has something wrapped around the shaft. Thus accounting for the shut down after initial power up.

Two visible wires are left unaccounted for :

The medium BLACK wire going to a wierd black connector.
And then there is the smaller white wire pair , which justify an RFI choke . . .so it could be the wire pair that goes to the units charger.

Still needed accounting for is the wiring that turns the unit on and speed control . . .if any.

The forthcoming BAAAAAAAAD news . . . . . . that is being a poured / hard potted module that stops all analysis by observation, excluding replacing any accessible bad power semiconductors on the heat sink.

What say ye . . . . .

73's de Edd
.....
Thanks 73's de Edd,
Surprisingly, the mower decided to start again today! ... I can only think that because of the good whether we've had here in the UK this last couple of days, if it was a damp connection, it's now had time to dry out?
I managed to mow the lawn with it this afternoon and noticed the engine didn't turn over on a couple of occasions, 'til the second or third attempt - but once running, was fine.
Thanks again for your help.
 

2Peter2

May 4, 2018
4
Joined
May 4, 2018
Messages
4
Have you looked in the manual for troubleshooting. Some of these the blinking light will tell you the issue. i.e. 3 blinks means this or 4 blinks means this. Maybe not for this, however generally a blinking red led is telling you something.

If not is sounds like there is a safety switch that tells you are still holding the handle that may have a bad or loose connection. I would start going through that portion of the circuit.
Hi Robert,
Nothing in the manual regarding the blinking light. However, the problem seems to have fixed itself!
Maybe a damp connection that's now dried out? ... not sure. Just glad it's working again.
Thanks for your input.
 

2Peter2

May 4, 2018
4
Joined
May 4, 2018
Messages
4
73's de Edd is one of the best failure analysis people I've seen on this site.
He's probably got troubleshooting information that will help you out.
I think you're probably right about water causing your problem.
My input, is that the last two electric mowers I've fixed, the switch itself has been the problem.
If you haven't already, I'd open the switch box that engages the mower motor and look inside of it.
Corroded contacts, broken plastic gear or lever parts; just to be sure that when you close the switch,
you're actually getting continuous power to the mower motor.
That's the first thing I'd check anyway.
Good luck.
Thanks shrtrnd,
it's working again now. A sunny couple of days may have dried a slightly damp connection.
Thanks for your help.
 
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