Mend Garden Tools, Lawn Mowers

Garden Tools, Lawn Mowers
Find out how to mend it for free.

Ask Question

Lawn Mowers

Mend Mend Garden Tools, Lawn Mowers

Faulty Bosch AL3640CV charger for Rotak lawnmower?


Have a 2 year old Rotak LiIon rechargeable lawnmower and the charger has stopped working. Indicator lights are dead on the charger - 13a fuse in plug ok, internal fuse also ok. Seems that there are a number of reports on various sites regarding dead chargers but no one with solutions for the repair. Looks like it is a common problem. Don't really want to buy a new one as it £70!

Any tips or even circuit diagram much appreciated.



April 2013
Just to add my huge thanks to Jet provost pilot & others for the fix described & the extra tips re. discharging capacitor, soldering to the existing resitor stubs etc - worked a treat. Saving ££ but more importantly a load of electronic waste going to landfill.

A joy to find something that can actually be fixed in today's 'disposable' society.

November 2020
I had the same problem. Luckily, I have friend with multimeter so was able to discharge the large 400 volt capacitor before doing any work. Also helpful was "Wolferls Repair Shop" video on YouTube (see It's in German but you can learn by just watching.
I sourced the 180k Ohm resister from RS Components who offer a fantastic range so I was able to choose the power and size. Great result!! Thanks to all.

Harry A
May 2020
Yep, worked for me too. I had two chargers that had both failed on me. The fix worked for both. Thanks alot Jet Provost!

Steve G
June 2019
I would just like to thank jet provost for the tip on how to repair Bosch battery charger,I bought four 180K resistors off the internet £1,66 inc P&P soldered new resistor as per instructions and bingo it works.

Many thanks Chris

September 2017
Just wanted to say thanks for posting this, its very helpful to get my charger working again. Also big thanks to "galooph", who had fixed the same thing and posted pic's of the resistors, on the board to find the faulty part.

August 2017
I had a faulty Bosch AL3620CV charger. I replaced the said resistor which I had identified as a 10MOhm with a similar 10Mohm 2W from ebay. Charger did not work. So replaced it with a 180kOhm 2W as suggested by Jet provost pilot and it works perfectly. Hope that helps someone.

June 2017
Thank you Jet provost pilot for your clear and concise instructions to repair the Bosch charger. Sadly for me I only found your instructions after I'd bought the replacement charger. The new one is a different design to the old and claims to be faster. Still I now have a spare thanks to you if the new one dies. Kind Regards and thanks again.

May 2017
hi wonder if you can help me my bosch al3640 charger is flashing red and green nad a relay is clicking with no batter inserted.. any thought how to fix..many thanks jb

February 2017
Jet provost pilot – thank you, you are a star! Your fix worked perfectly for me and saved me £75.
Thanks also to Louise for the link to pictures, John for the procedure on discharging the capacitor, and Martin for the tip about attaching the resistor leads.

January 2017
Thank you so much for taking the time to help us out! :) It worked for our faulty charger aswell. I would also like to add another link which also contains a description to solve the same problem, including pictures. These two saved us 150$! But more importanty it saves the planet from a heep of unnecessary electronic waste. Well done! You are the hero of the day! :)

July 2016
yes that does work BUT why has it gone , think you will find the fan is not working . ????

July 2016
Jet provost pilot you're spot on with all the detail. I cut defunct 180K 0.25W off PCB from top side. Then soldered new 2W resister to what was left of the old resistor wires. 2W is bigger, so bent wires to fit.

Top class advice that has saved me near on £100 for the sake of £1.49 from Ebay inc. P&P.

Back of the net!!!

Many thanks.

Mark Partridge
June 2016
To Jet provost pilot

Thanks for the tip, it worked for me also and saved me over £80 for 15 minutes work and £1.85 for a 180K ohm resistor.

June 2016
To Jet provost pilot

Thanks for the tip worked for me.

Regards Will

April 2016
Adding my thanks to Jet Provost. Fault was exactly as described. As a precaution I connected my mulit-meter set to 600V across the faulty resistor and waited while it slowly discharged the capacitor before replacing the resistor.

November 2015
LED's on my battery charger were not doing anything at all when plugged in and the charger would not charge the battery. I opened the case to prove power was actually getting to the battery charger and it was.
Replacing the resistor worked perfectly for me. I found it quite easy to cut the legs off the original resistor, cut down the legs of the new resistor and solder the new one on to the original cut down legs. This saved messing about with the under side of the PCB with the thick varnish coating.
Huge thanks to the original poster for the great description :-)

September 2015
Hi same problem as above does anyone know what amp the internal one is ?will buy new Amps today and hope it's just that thanks lisa

Lisa pearson
September 2015
Thanks Jet provost pilot, your fix worked perfectly

August 2015
Problem: not charging, fuse intact, no LEDs lit. Fault: the 180k resistor providing the start-up supply was open circuit.

W. M. Holliday
March 2015
my charger has both lights on but will not charge when I insert a battery. Green light come on on the battery when I press the on button
Just over 2 years old. can it be repaired?

lionel Crowe
September 2014
Maplin had 180k resistor at 2w so I soldered that in place of the baby one. Resoldered several times as the pcb is varnished heavily.
Plugged in mains and Big Bang.
The encapsulated soldered fuse had melted.
Gave up and ordered new charger at scandalous price for something just out of warrantee.

David T
August 2014
Yep it works just as you have said. Thanks for taking the time.

Fat Koala
August 2014
Worked for me too. Getting old resistor out broke copper circuit strip but managed to bridge it. Perhaps better to cut leads close to the old resistor and solder new one onto the remains.

July 2014
Reply to Jet provost pilot.

Thank you so much for taking the time to write this repair procedure out so clearly.

Best regards,

Computer Dave
May 2014
Had exactly the same fault and replaced the 180K resistor and it worked a treat. Thanks!!

May 2014
top tip - worked no problem, right down to getting a zap off the capacitor, total cost £1.32

April 2014
Open the case and remove the printed circuit board. Be careful not to touch the solder joints or the bare metal leads as the capacitors will hold a charge and zap you with a nasty shock.
OK with the battery connectors towards you look to the left hand side of the circuit board and you will see a big 150uF 400v capacitor, its an aluminium can about 20mm high 10mm dia with a black plastic sleeve and 150uF 400v on it. to the right see a component with coloured rings which are BROWN GREY YELLOW Its a 1/2 watt resistor. Its purpose is to be a pseudo load and discharge for the 150uF capacitor.
It blows/burns out without any visible sign of damage. replace it with a 180K Ohm 2 WATT resistor you can buy from ebay or if you are an electrician or electronics engineer Maplin sell 2 watt resistors you can cobble in series to make 180Kohm.
BINGO ! I think you will find it works.
If it doesn't then check the soldered in 2.5 amp fuse. Now the entire board and components are coated in varnish so you need to really scratch the varnish off to get a good connection for the meter leads.
If it still doesnt work ( though its unlikely ) replace the electrolytic capacitors ( the components that stand vertical with a plastic sleeve with something like 47uF 30v on them there are two.
I hope this helps.

Jet provost pilot
February 2014


Find out how to mend just about anything for free repair help, information and advice.

Can you help?

Are you an expert who can help answer questions? Click here to see the unanswered questions for each category.