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why does my makita go pop occasionally ?

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gerry madden16/01/2020 12:57:41
84 forum posts
38 photos

Hi all you electrical specialists....

I've had a Makita variable speed drill for nearly 30 years. In the long distant past I remember on one occasion getting an electrical 'pop' from around the switch area when running at low speed. It did it again yesterday, only this time it tripped the circuit breakers in the garage (where I was working) and the one in the house that feeds the garage. Thinking it was probably 'terminal' this time, I immediately stripped the drill to see what inside had failed.

I stripped the switch unit (which contained a small circuit board) and could see nothing amiss. No damage or signs of burning. I cleaned it all up and relubricated with Barrierta and reassembled. The device next to it was a dual capacitor. This looked old, a little swollen, but not conclusively busted in my modest opinion. So I put it all back together and tested the drill. All is well !

So what inside the drill might make a big pop noise, trip the trips and yet appear to be unaffected / undamaged ?

SillyOldDuffer16/01/2020 13:22:38
5138 forum posts
1074 photos

Posted by gerry madden on 16/01/2020 12:57:41:


The device next to it was a dual capacitor. This looked old, a little swollen,...

So what inside the drill might make a big pop noise, trip the trips and yet appear to be unaffected / undamaged ?

You said it, almost 100% sure to be that swollen capacitor. They're strapped straight across the mains and their purpose is to filter out interference that would otherwise broadcast freely off the mains wiring. The capacitors are highly-stressed, but, when they go pop, they fail open-circuit after upsetting the trip. When power is restored, everything works again apart from the capacitor. No problem except the drill is now unsuppressed. Without an electronic nappy the drill (EDIT mind the language) down the mains, which can upset nearby radios and internet connections!


Edited By JasonB on 16/01/2020 13:24:22

mgnbuk16/01/2020 13:29:07
601 forum posts
24 photos

If it just occasionally pops the runs OK again it could be a short through a build up of carbon dust around the brush holders. Used to see this quite a lot when DC main spindle motors were in common use - usually the drives would shut down with an overcurrent alarm, but when checked there was no measurable short as the flash over had burned the carbon build up away.

Nigel B

Maurice Taylor16/01/2020 15:28:42
56 forum posts
4 photos

I wouldn’t worry about interference to radios etc ,compared to interference put out by plasma teles and switch mode power supplies ,it will be minimal.

Andrew Johnston16/01/2020 16:10:33
5115 forum posts
594 photos
Posted by Maurice Taylor on 16/01/2020 15:28:42:

I wouldn’t worry about interference............

Depends upon the type of motor. A brushed DC motor is quite likely to be way noisier than a switch-mode PSU on a PCB.

Was the trip over-current or earth leakage?

Electrolytic capacitors are reknowned for swelling before failure. But I've not seen the same with other types of capacitor. Normally one would expect to see an X-rated capacitor across the supply and Y-rated capacitors from live and neutral to earth. If the equipment is double-insulated then there is no earth and no need for the Y capacitors. Both X and Y capacitors are metallised film and are self-healing as a short circuit failure is unacceptable. If the film is punctured the local metal film is designed to evaporate, removing the short circuit.

A picture would help identify the components, and possibly the problem.


gerry madden16/01/2020 17:23:06
84 forum posts
38 photos

Thanks all for the interesting points.

The drill is double insulated so no earth leakage. Not sure how then I would would get a L to N differential to flip the trips ?

There is some blackening on each end of the capacitor but decided it was probably dust from the seams of the clam-shell where the ends of the cap. resided. Perhaps I'm wrong. Your thoughts would be welcome.

Here's some pics.





Nicholas Farr16/01/2020 17:39:21
2067 forum posts
995 photos

Hi Gerry, that would be your suppressor blown, which would have been a short across the mains and activated your trips, needless to say the suppressor no longer works.

Regards Nick.

Ed Duffner16/01/2020 18:35:55
745 forum posts
61 photos

Hi Gerry,

The part might still be available from Makita or even an update to the switch and wiring, which Makita sometimes provide in the service bulletins. If you are in th UK and can provide the drill model number I could check on the Makita systems at work tomorrow(friday) if you like.

Just as a matter of interest, different countries sometimes have different switch and supression requirements for some of the Makita power tools.


gerry madden16/01/2020 19:49:51
84 forum posts
38 photos

Nick, since this is at least the second time its done this, would it imply that, as Andrew suggested, it is self-repairing to a degree and so must still have some 'suppresance' left in it even after a second loud pop ?

Ed, thanks for your offer. The model number is NHP1300S. I did some trawling on the web last night and references to this model tended to show up as diagrams and parts lists for HP1300S, which is not the same. (I think this ones's a fixed speed with a simple on/off switch and no suppressor.) And stranger still, I found the original instruction booklet at home from when I bought the tool and the diagram in respect of the switch and capacitor didn't match with reality very well at all. Its almost as though my variable speed version was a short-term upgrade that wasn't expected to be in production for long so they didn't waste too much time on documentation But if some OE parts are still available I might just buy them to keep the old girl going.


Nick Clarke 316/01/2020 21:50:33
518 forum posts
13 photos
Posted by gerry madden on 16/01/2020 19:49:51:

I found the original instruction booklet at home from when I bought the tool and the diagram in respect of the switch and capacitor didn't match with reality very well at all. Its almost as though my variable speed version was a short-term upgrade that wasn't expected to be in production for long so they didn't waste too much time on documentation But if some OE parts are still available I might just buy them to keep the old girl going.


Have you had the drill from new?? Although not the same brand, it was not uncommon to add the variable speed switch to B&D drills that were originally single or two speed - I have done several myself.

Edited By Nick Clarke 3 on 16/01/2020 21:50:57

old mart16/01/2020 22:13:03
1101 forum posts
113 photos

My Bosch drill does exactly the same, occasionally, more often at low speed than high, I haven't looked inside it for ten years when I replaced the horrible stiff cable with the lovely flexible B & D one after the B & D commutator decided to come unglued.

Nicholas Farr17/01/2020 10:10:24
2067 forum posts
995 photos

Hi Gerry, although your suppressor may be self healing, it doesn't necessarily mean that it is self repairing. As .Andrew has explained; the film evaporates and removes the short circuit. The black mark and the slight lifting of the outer wrapper on the end, suggests that this is what has happened. At best if it is still working, its efficiency is probably reduce somewhat and may cause radio interference, it should not affect the drill operating as it always has though. Maybe Andrew will enlighten you if it is any different.

Regards Nick.

gerry madden17/01/2020 14:33:10
84 forum posts
38 photos

Well, just done some suppression trials on the drill and sure enough I create some sharp pops and bangs on MW and LW as I cycle the trigger on my drill. Nothing on FM thankfully. There was no interference when running at steady continuous speeds though.

It's not often I listen to these bands when I'm drilling so wont be too personally affected but if I can buy a new suppressor I will.

What I did also discover whilst playing is that when cycling the trigger, occasionally it rotationally kicks much stronger than normal suggesting that the electrical power is being fed in suddenly rather than progressively. This only happened at small trigger movements at low speeds - exactly the conditions that have caused my suppressor to pop and my trips to flip. I don't think this is caused by mechanical deficiencies in the switch unit as this all looked good. So perhaps there's some speed/current conditions where the electronics create some spikes. May be this is what's caused the suppressor to fail a few times.


Ed Duffner17/01/2020 17:59:29
745 forum posts
61 photos

Hi Gerry,

According to the 'old' Makita service software, the capacitor part number listed for the NHP1300S is 645011-4. It shows up as "End of sales" on the new Makita parts ordering website. End of sales can mean obsolete or out of stock.


gerry madden17/01/2020 20:00:40
84 forum posts
38 photos

Thank you very much for your searching Ed. I'll do some digging see if I can find one somewhere.


Grindstone Cowboy17/01/2020 20:24:29
194 forum posts
11 photos

These people seem to have them in stock and not expensive either. No connection with the company, just turned up in a search for the part number Ed supplied.

gerry madden17/01/2020 20:43:51
84 forum posts
38 photos

Thanks G/C ! In fact I found the same just a few moments earlier. There was another priced at 30 something pounds which is what I was actually expecting... I consider myself lucky !


gerry madden25/01/2020 18:20:57
84 forum posts
38 photos

Oh dear sometimes things are straightforward, sometimes not. I ordered 645011-4 and I'm sent 645006-7. Its probably an appropriate equivalent however the real issue is that its completely the wrong part . Had I delved deeper when I opened the drill the first time, I would have seen the real suppressor was lurking below the reversing switch - left hand object in the picture below.


What I was expecting was the 3-wired yellow thing on the right. The black suppressor has the Makita part number on it which ties up with the number given on here. However the yellow thing has lots of numbers but nothing resembling a Makita number. Strangely I cannot find even a parts diagram for this model drill that shows this item. Perhaps the yellow thing is part of the electronic switch unit, or even the field winding (as one lead disappears into this unit), I don't know. But if this particular part is unidentifiable, let alone buy, perhaps I should just keep using the drill and put up with the once-every-two-year 'pop and trip'.


gerry madden25/01/2020 19:04:11
84 forum posts
38 photos

As I mentioned in the previous post, the middle lead from the yellow thing goes into a hole in the laminated core of the field windings. I pulled at it and it came out relatively easily to reveal a coppered spiral spring-like thing. As a single lead it cant be a temperature sensor. So any ideas ?


Grizzly bear25/01/2020 19:22:33
214 forum posts
6 photos

Hi Gerry, Can you take a close-up photo of your yellow whatsit .

I would imagine it's a mains filter.

Good luck, Bear..

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