Power tool repair event, can you help?


Hi, Laura from Restart here :wave:

We’re working on designing a power tool repair event, probably focusing on drills, as this is one of the most common hand-held products in this category seen at repair events.

Looking for someone who has quite a bit of experience in power tool repair who could help with any safety advice (such as battery v mains preference), or could maybe suggest another common household power tool that easier to repair/demo? Maybe a hand-sander?

The repair demo would only last 30mins and we want it to be quite hands-on for the participants.

Any thoughts/suggestions welcome.

Many thanks


Hi Laura

I’ve done some power tool repair, on the whole fairly successfully, although this is at home not in a repair event: a cordless drill, mains drills, mains plaster stirrer, mains hammer drills/angle grinders, kitchen mixer. I described at least three of those repairs in the ‘Today I fixed’ thread :slight_smile: For all those the mechanicals were mostly fine (apart from one old mains drill) it was the electrical side that had problems; on the whole this is good because mechanical side is harder/impossible to repair have to buy replacement parts or find a not-quite-so-broken donor to scavenge from.

Battery powered is definitely safer. For mains ensure it’s relatively safe by always doing a PAT check/test first, and use an RCD socket to give some protection. Of course power tools usually means spinning/cutting/vibrating is involved that also needs care to make sure that doesn’t injure/damage anyone.

As always if mains is involved keep your work area free of clutter/kids/drinks/food/crowds.

I’d avoid a sander if you can because they’re just a bit exciting to power on without sanding your bench or vibrating all those little parts you put down on the bench off the bench onto the floor.

A drill is good, but otherwise why not a kitchen mixer (is it a ‘power tool’?), the type with two beater heads, the Kenwood Chef type standing mixers are (I suspect) nice from a repair perspective you probably end up doing a lot more disassembly than with something smaller.

Different types of faults/problems I’ve seen:

  • Most basic is: is it getting power? invisible breaks in mains leads or difficult-to-see problems in the internal wiring, flat battery which you thought was charged, broken connection inside the battery, …
  • Don’t rule out that there might be more than one problem in the power lines - one drill had a break hidden in the mains wire and a problem with the brush holder connection having become disconnected, … and both allowed the drill to work intermittently, which was confusing…
  • Getting the thing apart without dropping parts/gears/grease everywhere - and being able to reconstruct it! Take photos, be ready for things to drop out, …
  • Tactics for avoiding those tedious/time-consuming/risky multiple disassembly/reassembly/test/fail/ iterations (IIRC the plaster stirrer took me three iterations, the pesky drill with the intermittent power breaks took five) - don’t assume the first fault you find is the only one, wiggle every single connection, meter the wiring for breaks while wiggling, …
  • Maintenance you could do while you’ve got it apart, but should you do it? - e.g. should you put new brushes in? I’ve been bitten by trying to do maintenance like on the plaster stirrer wanting to change the brushes because they might have been why it wasn’t working ended up making the whole repair harder when OK they might have been not quite right they weren’t actually the root cause which was the electronic speed control. Personally I’d tend to change them given the chance, but it’s unlikely you’d have stock of any random brushes you might come across, so it also makes the overall repair slower. Always clean out grot/crud/dust if you can.
  • What can you actually measure to help you diagnose - if the device has any electronics in line with the power, as is common these days of electronic speed control, even a power drill with a squeeze-harder-to-go-faster trigger has electronics in the trigger unit which won’t be show low/zero resistance on your meter however hard you squeeze it. Same for Dyson battery powered sucky cleaners, there’s no simple direct connection from battery to whizzy motor that you can help you check for connectivity. But you can check battery to speed control input, speed control out to motor, motor resistance, etc… And if you can somehow connect a battery while the electronics is accessible then you can check voltages wrt the -ve of the battery look sensible.
  • When to stop disassembling (because every additional part you remove increases risk of something breaking/getting lost and increases difficulty of reassembly)? This is a conflict with the need to confirm that the thing you think is the problem isn’t actually the only problem. Difficult. Check everything you can at the point you’re at rather than turning the thing into a complete kit before checking for problems because while this may be a satisfying demonstration of your disassembly skills you’re risking reassembly problems.
  • The things you can’t repair - broken gears, slidey contacts that don’t slide and/or contact any more, broken casing (which for a mains-powered thing is probably a PAT test fail anyway), …
  • Blockers - brushless motors quite common in battery powered devices don’t have a conventional (and really very simple) commutator instead using electronic switching phased between multiple stator coils around a permanent magnet in the rotor, using an encoder on the end of the rotor which has sensors to tell the electronics what angle the rotor is at, allowing the electronics to appropriately drive the stator coils to attract the magnet to rotate in the whichever direction. All that electronic complexity means no commutator, no need for brushes, no need for rotor windings - so mechanically simpler (and cheaper) with no maintenance ever really, but there’s more high-current electronics which can go phut and be difficult/impossible to diagnose a fault or repair it. Never had to look at one of these but if the problem is the brushless drive electronics it’s unlikely to be repairable except by a replacement electronics module. However you won’t know that until you’ve eliminated all the usual suspects of wiring/power connectivity and battery.
  • Novel design - the only example I have of this is a heavy Bosch mains drill which had a twistable collar which reversed the direction by reversing the connections to the motor, involving an intricate design of contacts onto brass conductor strips. This wasn’t making contact in one direction and took a lot of fiddling to understand why it wasn’t working and to clean the sliding contacts and get it working, at least for a while.



Thank you Ian - that’s really helpful :+1:

For my part, I haven’t had a great success rate with power tools but internal switches failing, motor brushes needing replacement and a requirement for general maintenance have been the ones that succeeded.

I think cordless vacuums are a good “low hanging fruit” as the most common failures are related to dust cloggages, and wire breaks in the carpet head.

Thinking from a waste prevention perspective, I suspect that one of the major causes of drills being disposed of is nickel (Ni-MH or Ni-Cd) batteries dying and owners recognising the superiority of modern lithium ion batteries.

I have started a long term project 3D designing replacement battery cases for old nickel battery drills so that lithium batteries can be used instead. 2 out of 3* conversions were huge successes, with the drills performing better than new after the upgrade. I now need to think about whether it’s possible to scale the intervention.

The challenge is the join between the battery and the terminals of the drill, for which I think the best method is reusing the part from the old battery casing.

The next challenge is how to scale-ably design the clipping interface between the battery and the drill. I am leaning towards a semipermanent attachment method (screws for example) and adding a USB-C charging port to the drill. This has the advantage of ensuring a new charger is not required, but does add a little cost** as a boost PCB is needed for 18V drills.

* The one that failed was an old B&D drill that had an insane current draw, over 50A, and therefore needed more than the 30A that a 1S 21700 battery pack could provide.

** The cost is about £12.50 for 5 cells, £2 for the circuitry and £1 for the printer filament.


A very good topic, and some excellent suggestions already. “Power tools” covers a wide field, although increasingly at my Repair Cafe we are seeing more battery-powered devices.

I’ve also been upgrading several (of my own) battery drills, vacuum cleaners etc by rebuilding the failed battery packs, using multiple small Lithium-ion batteries reclaimed from spent disposable vapes or from defunct laptop batteries, many of which will yield good cells with decent remaining life. With care, proper testing, and a cheap protection PCB, the performance will probably better than new, and I’m preventing landfill from two directions!

However, as will be obvious, this takes a lot longer than could be demonstrated in a Repair Cafe setting. We tend to quickly identify whether the fault is in the tool, the charger or (99% of the time) the battery. One particularly annoying facet of rechargeable batteries is that manufacturers tend to design a new battery pack for each release of tool, meaning that when the old battery expires, it has been discontinued and the battery for the current model won’t fit.

Replaceable cells are perfectly feasible, even in high-current applications, and the 18650 Lithium-ion cell is ubiquitous. Why not design a power tool to take replaceable cells? I can only assume that this would be a less profitable approach for manufacturers.


Hi Laura - how’s your event planning going?

I’ve got a mains drill (Makita HR2470) in pieces at the moment which could demonstrate disassembly gotchas even getting to change the brushes.


Hi @Laura_4720 are there still plans to do this?

I’ve currently got a Ryobi One+ 18V oscillating multitool in my TODO crate, but that mostly needs its vibration-damping mounts replaced because they’ve worn out: the only electrical issue is a loose connection, almost certainly caused by the vibration.

At the South London Maker Space event, someone turned up with a cordless impact driver whose brushless motor had failed but I had to give up on that one due to lack of time: it looked like the failure might have been in the motor control circuit.

(Maybe someone who knows more about brushless motors than me could do a wiki page on them :smiley: ?)

BTW ifixit.com has some info on power tools, but I haven’t dug into it yet.

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