Intermittent operation SDS drill - help!

My sds drill (Bosch GBH 2-24 DFR) has developed a fault when sometimes you pull the trigger and get nothing, tip it vertical (or maybe give it a knock) and it's ok.

I've had it apart and checked for low-ohm across every single connection - coils, brushes, reversing switch and main switch - all exaclty what you'd expect.

The fault seems orientation dependent - particularly pronounced when it's horizontal (tip it off horizontal and it runs fine, back to horizontal and it doesn't, tip it downwards and it's ok again, back to horiz - arrrgh! - etc).

The only thing I can't check is the speed-sensitive part of the switch (there's a direct contact as well- for the supressor cap - which I can check, and is ok).

So how do these speed senstive switches work? Is there a variable resistance in there?

The power switch is =A326, so unless it's a fairly certain suspect, I'd be reluctant to buy one.

Parts diagram here:

formatting link

Reply to
dom
Loading thread data ...

I think it's something mechanical with the hammery mechanism. Sometimes SDS drills do need to be "started" by knocking the tip into the workpiece.

Owain

Reply to
Owain

Reply to
EricP

See the line above that starts with the word connection! Is the cable OK where it enters the drill body, sometimes with metal fatigue the inner cores break down. Try pulling the trigger and wiggling the cable.

HTH

John

Reply to
John

Yes - visually checked them - lots left, well sprung onto the rotor, solid connections. I also checked continuity from the live pin of the plug through to the input side of the switch (0.4 ohm), and from the output side of switch right through to the neutral pin of the plug (15 ohms).

So I guess that pretty much leaves the speed-sensitive switch.

Can anyone tell me if it might be worth breaking the switch open and what sort of circuit/position-sensing they use?

Reply to
dom

Usually come adrift within about 100mm of the cable clamp. HTH [as well]

Reply to
Grumpy owd man

Yup - cable checked!

Reply to
dom

Can you strap the switch out completely and see if the fault disappears or remains ?

Andy

Reply to
Andy Cap

Cable checked AGAIN, and "wiggle the cable and the continuity buzzer goes on and off" FOUND!

Thanks guys for your help.

And just shoot me for waffling about such a simple fault.

Reply to
dom

Intermittent continuity fault on the cable!

Reply to
dom

Well you found it before I could suggest that. Never forget Occam's Razor! I was about to dismantle the inside of the car the other day before I realised that the intermittent flickering of the interior light while driving could be fixed by slipping a packer under the tailgate switch.

Reply to
Newshound

Funnily enough, this drill did have that fault too (intermitent hammer action). Turned out to be a problem with hammer selector switch not properly engaging the whotsit that slides a "layshaft" in the gearbox.

Reply to
dom

with Hiltis, don't be tempted to just cut a bit back from the trigger - the fault could be 3 or 4 feet down the line.

Reply to
Phil L

As a tip, and this goes for anyone else who owns an sds that has hammer only...make sure you swap over from drill to hammer from time to time otherwise the insides can sieze, that is to say, if you use it predominantly for drilling holes, every now and then, swap it over to hammer and chisel a few lumps of concrete up, likewise if it's predominantly a breaker, drill a few holes every week or two, and a squirt of grease down the chuck will do it no harm neither.

Reply to
Phil L

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.