Dremel 395 VSC repair

[civ]

Hello again:

I have a Dremel 395 rotary tool with variable speed control.
After acting up almost from the very start, the said VSC finally went
south, with the contacts in the sliding switch severely damaging the
tracks, now useless.

Acting on common sense (remains to be seen), I decided that the best
thing would be to wire it straight and then see about a different /
external speed control instead of spending money on a new one.

The original never worked properly and IMHO is flimsy, to say the
least.

The unit now works perfectly well but only at full speed and many
times I need to reduce it to more manageable RPMs ie: 75%, 50%, 30% of
the 33K RPM full speed.

Before getting something else, I'd like to see about taking advantage
of the ceramic board and the components as the only parts that are
damaged are the tracks.

Here's a photo of one of those ceramic VSC boards, posted by someone
with a different problem at imageshack which shows the tracks in
perfect shape. (Thanks!)

http://img135.imageshack.us/img135/6369/vsc2gg8.jpg

The sliding switch has three contacts which form part of the same
piece of brass: the first contact slides on the dark track, the second
contact slides on the silver track and the third contact slides on a
brass track in contact to one of the graphite brushes.

Far left = min. speed
Far right = max speed

The other brush connects to the solder contact seen at the right of
the surface mount capacitor.

In order to be able to use this same VSC board, what would I have to
use to replace the function of the tracks?

A potentiometer between the solder contact seen at the right of the
surface mount and the ground tab on the (?) voltage regulator?

Thanks in advance,

CIV

 

[N_Cook]

civ <sawbona@flashmail.com> wrote in message
news:c949b20e-3f65-4e1e-a745-016315056fc2@h21g2000yqa.googlegroups.com...

Hello again:

I have a Dremel 395 rotary tool with variable speed control.
After acting up almost from the very start, the said VSC finally went
south, with the contacts in the sliding switch severely damaging the
tracks, now useless.

Acting on common sense (remains to be seen), I decided that the best
thing would be to wire it straight and then see about a different /
external speed control instead of spending money on a new one.

The original never worked properly and IMHO is flimsy, to say the
least.

The unit now works perfectly well but only at full speed and many
times I need to reduce it to more manageable RPMs ie: 75%, 50%, 30% of
the 33K RPM full speed.

Before getting something else, I'd like to see about taking advantage
of the ceramic board and the components as the only parts that are
damaged are the tracks.

Here's a photo of one of those ceramic VSC boards, posted by someone
with a different problem at imageshack which shows the tracks in
perfect shape. (Thanks!)

http://img135.imageshack.us/img135/6369/vsc2gg8.jpg

The sliding switch has three contacts which form part of the same
piece of brass: the first contact slides on the dark track, the second
contact slides on the silver track and the third contact slides on a
brass track in contact to one of the graphite brushes.

Far left = min. speed
Far right = max speed

The other brush connects to the solder contact seen at the right of
the surface mount capacitor.

In order to be able to use this same VSC board, what would I have to
use to replace the function of the tracks?

A potentiometer between the solder contact seen at the right of the
surface mount and the ground tab on the (?) voltage regulator?

Thanks in advance,

CIV

The components on my earlier model, for 240V ac use
Dremmel Mod 358, ser 5-13, minidrill
Triac BT24A, 100nF 250V, 10K,4.7K, 390K , 56R
and log pot that measured 220K max, in cct

only switch is on/off, speed varied by pot

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Jim Yanik]

"N_Cook" <diverse@tcp.co.uk> wrote in news:h42376$vc6$1@news.eternal-
september.org:

civ <sawbona@flashmail.com> wrote in message
news:c949b20e-3f65-4e1e-a745-016315056fc2@h21g2000yqa.googlegroups.com...
Hello again:

I have a Dremel 395 rotary tool with variable speed control.
After acting up almost from the very start, the said VSC finally went
south, with the contacts in the sliding switch severely damaging the
tracks, now useless.

Acting on common sense (remains to be seen), I decided that the best
thing would be to wire it straight and then see about a different /
external speed control instead of spending money on a new one.

The original never worked properly and IMHO is flimsy, to say the
least.

The unit now works perfectly well but only at full speed and many
times I need to reduce it to more manageable RPMs ie: 75%, 50%, 30% of
the 33K RPM full speed.

Before getting something else, I'd like to see about taking advantage
of the ceramic board and the components as the only parts that are
damaged are the tracks.

Here's a photo of one of those ceramic VSC boards, posted by someone
with a different problem at imageshack which shows the tracks in
perfect shape. (Thanks!)

http://img135.imageshack.us/img135/6369/vsc2gg8.jpg

The sliding switch has three contacts which form part of the same
piece of brass: the first contact slides on the dark track, the second
contact slides on the silver track and the third contact slides on a
brass track in contact to one of the graphite brushes.

Far left = min. speed
Far right = max speed

The other brush connects to the solder contact seen at the right of
the surface mount capacitor.

In order to be able to use this same VSC board, what would I have to
use to replace the function of the tracks?

A potentiometer between the solder contact seen at the right of the
surface mount and the ground tab on the (?) voltage regulator?

Thanks in advance,

CIV



















The components on my earlier model, for 240V ac use
Dremmel Mod 358, ser 5-13, minidrill
Triac BT24A, 100nF 250V, 10K,4.7K, 390K , 56R
and log pot that measured 220K max, in cct

only switch is on/off, speed varied by pot

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

I have a Dremel model 270(single speed),and I use an ordinary lamp dimmer
as a speed control.
I mounted it in a double outlet box with a duplex outlet that gives a
variable outlet and a full 120VAC outlet.
Then you can also use it as a soldering iron temp reducer.

--
Jim Yanik
jyanik
at
kua.net

 

[Wild_Bill]

I believe you'll find that the wide, black strip on the "board" is
essentailly the same as the resistive element of a speed pot. It would be a
resistive compound deposited directly onto the ceramic substrate.

The contacts on the button would seem to be acting as the wiper section of a
speed pot, while also creating a path for one of the motor brushes.

If you are going to proceed with eliminating and substituting the original
"board" speed pot, you would need to bypass the wide, black strip, in ase it
is still condutive from one end to the other.

There are likely to be numerous examples of light duty triac circuits
online, since many applications and products use this very basic circuit.

I've been using a foot speed control for a while now, and this method is
very convenient and easy to get used to.
Not only that, but the foot speed control is very versatile, as it has a
power cord receptacle for plugging tools into, so it can be used for
numerous small power tools.
Other small AC/DC universal motors can/are conveniently used with it.

There are other products that would perform well as a method to vary speed
(or temperature in the case of low-power heaters, soldering irons, for
example).

One product is commonly referred to as a router variable speed control,
which is functionally, essentially the same circuit as the Dremel varaible
speed circuit, but rated for up to 15A (which is a lot higher than the
Dremel's demand).

As for the foot speed control, I was kind-of expecting to see a circuit
board when I opened the housing (as I usually always do), but the only part
inside the sort-of unique housing is a trigger switch from a variable speed
drill (rated for 6A).
The Linemaster and Foredom units are just fancy boxes with drill trigger
switches in them.

--
Cheers,
WB
..............


"civ" <sawbona@flashmail.com> wrote in message
news:c949b20e-3f65-4e1e-a745-016315056fc2@h21g2000yqa.googlegroups.com...

Hello again:

I have a Dremel 395 rotary tool with variable speed control.
After acting up almost from the very start, the said VSC finally went
south, with the contacts in the sliding switch severely damaging the
tracks, now useless.

Acting on common sense (remains to be seen), I decided that the best
thing would be to wire it straight and then see about a different /
external speed control instead of spending money on a new one.

The original never worked properly and IMHO is flimsy, to say the
least.

The unit now works perfectly well but only at full speed and many
times I need to reduce it to more manageable RPMs ie: 75%, 50%, 30% of
the 33K RPM full speed.

Before getting something else, I'd like to see about taking advantage
of the ceramic board and the components as the only parts that are
damaged are the tracks.

Here's a photo of one of those ceramic VSC boards, posted by someone
with a different problem at imageshack which shows the tracks in
perfect shape. (Thanks!)

http://img135.imageshack.us/img135/6369/vsc2gg8.jpg

The sliding switch has three contacts which form part of the same
piece of brass: the first contact slides on the dark track, the second
contact slides on the silver track and the third contact slides on a
brass track in contact to one of the graphite brushes.

Far left = min. speed
Far right = max speed

The other brush connects to the solder contact seen at the right of
the surface mount capacitor.

In order to be able to use this same VSC board, what would I have to
use to replace the function of the tracks?

A potentiometer between the solder contact seen at the right of the
surface mount and the ground tab on the (?) voltage regulator?

Thanks in advance,

CIV

 

[civ]

Hello:

Thank you so much for such a fast reply.
Much appreciated. =-)

The components on my earlier model, for 240V ac use Dremmel Mod 358, ser 5-13, minidrill
Triac BT24A, 100nF 250V, 10K,4.7K, 390K, 56R and log pot that measured 220K max, in cct
only switch is on/off, speed varied by pot
Mine is also 220v, the one in the photo is 110v but identical in

layout.
I'll check and see about the similarities in components and have a try
with a 220K log pot across the in/out of the board and measure the
output voltage.

It would be good to be able to use the same circuit the thingie came
with.
Glue it on a small Al heatsink and put it inside an empty wall-wart
with the AC cable going through.

---

I have a Dremel model 270 (single speed), and I use an ordinary lamp dimmer ...
I've tried with a lamp dimmer I have but it does not work properly as

it barely reduces speed before starting to stammer.
Probably because of the type of load. (?)

Thanks a lot to both of you for your input and suggestions.

Best regards,

CIV

 

[Nicholas Bodley]

On Mon, 20 Jul 2009 14:08:45 -0400, Wild_Bill wrote:

variable speed control,

I s.t.r. triac speed controls for motors that compensate for load torque,
so the no-load speed holds fairly(?)(quite?) well under load.

There's a lamp dimmer made to be installed on ordinary "zip" lamp cord;
it worked very well for me for years as a soldering iron power control,
giving a great range of temperatures. I made a light-duty extension cord
that used it.

These days, I'd worry about line spikes reaching the tip, capacitively
coupled, although good modern ones probably have the shank connected to
safety (earth) ground. Have no iron just now, but will get a soldering
station when I spring for one.

--
Nicabod =+= Waltham, Mass.

 

[whit3rd]

On Jul 20, 11:27 am, civ <sawb...@flashmail.com> wrote:

I have a Dremel 395 rotary tool with variable speed control.
After acting up almost from the very start, the said VSC finally went
south, with the contacts in the sliding switch severely damaging the
tracks, now useless.

Easiest way to control these is with a variac (variable
autotransformer);
somewhat costly, but it's a useful item for lots of other things,
too.

Motor control rated 'dimmer' type devices are also available; the best
are those intended for inductive loads, like 12V transformers driving
halogen lighting (Lutron and other manufacturers make these
in convenient wallswitch form). Incandescant-light dimmers are
slightly different, and might work well or poorly.