Spares for 'Hymoto' cordless drill ?

[Adrian]

Hi All

Very much a long shot here.....

I was given a fairly decent (by my non-professional standards) Hymoto cordless drill-driver.

On investigation, it seems to be a 'Chinese copy' of something or other - but it's got bags of power, 2 spare 24v batteries, and it's far and away the best tool of its sort that I've owned (can't afford 'proper' cordless kit like bosch or makita!)

Anyway - the bad news - the variable speed function has packed up (after an afternoon spent inserting about 200 30mm screws to hold down a plywood floor!) It's now very much a 'digital drill' - either full on or full off

On dismantling the thing, there's a trigger mechanism that includes a tiny PCB with a printed-on carbon track and a surface-mounted IC, this drives a power mosfet on a fairly small heatsink. Should vary the speed of the motor - but doesn't !

Turns out the power mosfet is a fairly cheap part - so tried a new replacement part - but still no speed control....

So - I'm a bit stumped.... Possible courses of action

- reverse engineer something on veroboard to drive the mosfet

- chuck the thing away

- live with the tool as a powerful 'on-off' drill...

- locate a spare trigger assembly (I did email Hymoto but they didn't bother to answer me.....)

Any ideas please ? - or leads on where I might get spares ??

Thanks Adrian

[Phil L]

Get a new one, they've come down quite a bit in price over the past 12 months...don't throw that one away though, you must do what I do and store it away in the shed and have thoughts like, 'just in case..' and 'I might need it someday' and, 'I'll fix that if and when I get time / parts / both'

[Pete C]

The IC is probably a bog standard PWM controller, any markings on it?

cheers, Pete.

[Adrian]

A man after my own heart I already have four 'older' cordless drills.

The original one (Peugeot) had the nicads 'die'. After they were replaced the charger gave up the ghost.

The other 'broken' one had a short on one of the cells - which took out the charger.

The two which 'sort of' work are just about OK, the battereis don't last long - but they have nothing like the power that my recently-died drill has.... as I say - the Hymoto now has only 2 speed positions (off and maximum) - which makes it ok for whacking holes into walls for shelves etc - but is a bit un-subtle for screwdriving....

On looking around - a 'branded' drill of similar power with 2 batteries looks to be upwards of £100 - which will have to wait...

Thanks for the comments Adrian

[Adrian]

Dunno - I'll have a look when I've got a moment.

The IC is on a tiny pcb, which is inside the trigger switch mechanism, which is inside the drill body .....

Takes a few minutes to get inside, and longer than that to read the markings !

I'm not convinced that the 'mechanicals' of the trigger mechanism are doing what they should. There's the innards of two 'rocker' switches in there - one comes on as soon as you depress the trigger, and the other switches at 'maximum'. I guess the first one disconnects the braking diode across the motor and applies general power to everything, while the other one (presumably) puts the battery straight across the motor at max trigger.

I guess a few minutes with a scope would confirm whether or not there's 'anything' going on with the pwm circuit....... I suspect it's 'dead'. Shame - the power fet was only a euro or so, and was very easy to change - would have been nice if that'd fixed it ......

I wondered about making something up with a '555 - not necessarily to use the speed control on the existing trigger, but maybe controlled by a little pot 'somewhere'.

Actually - what would be really handy would be a 'soft start' control

- so's the thing didn't start at 'maximum'. It has a 2-speed gearbox and 12-position torque setting - so with a 'gentle start' it might just do for screwdriving....

Having said that - I don't intend to have to do another marathon screwdriving session. The last one was only to get a decent surface to take some new vinyl after I'd wrestled with removing the hideous black & white tiles in the bathroom. It ended up being a lot quicker, having chipped the tiles off and being left with the adhesive, to gripfill & screw some 9mm ply down - rather than spend another 2 days chipping off the adhesive. Don't want to play _that_ game again !

Thanks for the comments - I'll see if there's any ID on the chip - are these things readily available, then ??

Thanks Adrian

[Pete C]

Did a bit of 'extreme dismantling' last night on a NuTool I had lying around, found much the same as you, drill speed controller with a tiny little 8 pin chip inside.

The chip had DK1 2036 on it which I can't find anything on, '2036' could be a year/week code.

In your case it may be the pot, poss worth soldering a thin wire somewhere to check the voltage from the wiper?

In any case I'd expect it's worth hanging onto the drill, often the batteries go and people end up with a spare handle. Somthing of a similar type and vintage to yours is quite likely to have the same bits.

cheers, Pete.

[Adrian]

Could well be a custom-made thingy then ??

I was thinking the same thing myself. Once the trigger assy is put together then you can't see inside it to probe it..... catch 22 !

That's a thought. I did have a sort of an ambition to play with PICs - this might just be the excuse I need

Adrian

[Pete C]

Probably, little market for cheap drill controller ICs outside China...

Maybe put a 555 thing in the handle somewhere, and wire it in using the pads of the old chip:

Just say NO!!! You'll be into ethernet connected MCUs before you know it! :)

cheers, Pete.

[Adrian]

Now there's a couple of interesting links - thanks very much.

Interesting that the first link seems to describe a similar fault condition to mine - which could well indicate that the PWM chip is itself at fault....

All I'd need to be able to do is access the pot in the trigger assembly.....

Got a box full of 555's in the shed ...and there's a fair bit of room in the handle of the drill where one could 'lose' a little bit of veroboard..... ...need to _find_ a bit of vero first - we just moved house.....

The slippery slope, eh ??

In another life I worked on much the same sort of kit - but that were in the days when microcontrollers consumed amps....... !

Perhaps the '555 approach is going to be easier to realise in the short-term.......

Thanks for the weblinks!

Adrian

[Pete C]

Yes, you'll be a victim of 'debug addiction'...

cheers, Pete.