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 £26, so unless it's a fairly certain suspect, I'd
be reluctant to buy one.

Parts diagram he
http://www.mtmc.co.uk/prodtype.asp?P...ageHistory=cat

On 29 Nov 2006 09:36:57 -0800, " wrote:

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 £26, so unless it's a fairly certain suspect, I'd
be reluctant to buy one.

Parts diagram he
http://www.mtmc.co.uk/prodtype.asp?P...ageHistory=cat

Are the brushes ok?

"EricP" wrote in message
...

On 29 Nov 2006 09:36:57 -0800, " wrote:

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 £26, so unless it's a fairly certain suspect, I'd
be reluctant to buy one.

Parts diagram he
http://www.mtmc.co.uk/prodtype.asp?P...ageHistory=cat

Are the brushes ok?

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

Are the brushes ok?

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?

As above, remove cable cover and pull the cores of the flex.
Usually come adrift within about 100mm of the cable clamp. HTH [as
well]


--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

Try pulling the trigger and wiggling the cable.

Yup - cable checked!

On 29 Nov 2006 10:13:48 -0800, " wrote:

Are the brushes ok?

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?

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

Andy

wrote:
Try pulling the trigger and wiggling the cable.

Yup - cable checked!

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.

Intermittent continuity fault on the cable!

wrote in message
oups.com...

wrote:
Try pulling the trigger and wiggling the cable.

Yup - cable checked!

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.

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.

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.

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.

wrote:
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 £26, so unless it's a fairly certain suspect, I'd
be reluctant to buy one.

Parts diagram he
http://www.mtmc.co.uk/prodtype.asp?P...ageHistory=cat

Change the whole cable from plug to trigger, I've done it a hundred times
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.

wrote:
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.

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.

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.