A friend has a Dremel model 1680 16 inch variable speed scroll saw. The
motor started working intermittently and shortly after that it stopped
working completely. The motor itself is fine since if the power is wired
directly to it the saw will run with no problem. This means the fault is
on the speed control circuit board. The problem with this is the fact
that Dremel has sanded off the part numbers on the two IC's on this
board so we have no idea just what they are or what the pinout would be.
Does anyone know where I might locate a schematic of this board so I can
troubleshoot it and see what the problem is? Or, if someone out there
has one of these puppies that has a fried motor and they want to part
with the speed control circuit board then let me know and I will pass
the info along to my friend. Thanks in advance.

Cheers,
Lawrence

My first action would be to contact the mfgr and see what replacement
parts are available and costs, etc. Also ask for a schematic. Try
Googling on the model number.

H.R.(Bob) Hofmann

wrote:
My first action would be to contact the mfgr and see what replacement
parts are available and costs, etc. Also ask for a schematic. Try
Googling on the model number.

H.R.(Bob) Hofmann




If they sanded off the numbers they most certainly won't supply a schematic.

I'd first suspect cracked solder joints, if those are all ok then look
into the power component, almost certainly a triac which controls power
to the motor. If all else fails you could build a new speed control from
scratch, they need not be very complicated.

"James Sweet" wrote in message
news:eGGvf.455$ww5.161@trnddc01...
wrote:
My first action would be to contact the mfgr and see what replacement
parts are available and costs, etc. Also ask for a schematic. Try
Googling on the model number.

H.R.(Bob) Hofmann

If they sanded off the numbers they most certainly won't supply a
schematic.

I'd first suspect cracked solder joints, if those are all ok then look
into the power component, almost certainly a triac which controls power to
the motor. If all else fails you could build a new speed control from
scratch, they need not be very complicated.

J is correct ... of components - look first at the Triac .. most TO-220
versions are 400 V or 600 V models at no more than 4 to 8 amps.

gb

Lawrence writes:

A friend has a Dremel model 1680 16 inch variable speed scroll saw. The
motor started working intermittently and shortly after that it stopped
working completely. The motor itself is fine since if the power is wired
directly to it the saw will run with no problem. This means the fault is
on the speed control circuit board. The problem with this is the fact
that Dremel has sanded off the part numbers on the two IC's on this
board so we have no idea just what they are or what the pinout would be.
Does anyone know where I might locate a schematic of this board so I can
troubleshoot it and see what the problem is? Or, if someone out there
has one of these puppies that has a fried motor and they want to part
with the speed control circuit board then let me know and I will pass
the info along to my friend. Thanks in advance.

Have you checked for bad solder connections?

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Thanks for all the responses so far. I have already gone over the board
checking solder joints. Actually that is the funny part cause the fellows I
work with say I must have microscope eyes since lots of the stuff we work on
I can pick out bad solder joints with one eye tied behind my back ;-)
I haven't really had time yet to check out the triac on the board or any of
the transistors and stuff. During the brief time I saw the board I just
happened to notice the chips sanded off so I thought I would ask if anyone
had a schematic so I can have all my info handy before I start working on it
later in the week. I have found places that sell the board for around $60.00
so if all else fails the owner can get another board. I'm on days off at the
moment and I'm back to work on Tuesday so that is when I will get my hands
on it again to start checking out the board at component level. Like I said,
I was just seeing if I can get all my ducks in a row beforehand to make life
a little easier. Thanks again folks.

Cheers,
Lawrence

"Lawrence" wrote in message
...
Thanks for all the responses so far. I have already gone over the board
checking solder joints. Actually that is the funny part cause the fellows
I
work with say I must have microscope eyes since lots of the stuff we work
on
I can pick out bad solder joints with one eye tied behind my back ;-)
I haven't really had time yet to check out the triac on the board or any
of
the transistors and stuff. During the brief time I saw the board I just
happened to notice the chips sanded off so I thought I would ask if anyone
had a schematic so I can have all my info handy before I start working on
it
later in the week. I have found places that sell the board for around
$60.00
so if all else fails the owner can get another board. I'm on days off at
the
moment and I'm back to work on Tuesday so that is when I will get my hands
on it again to start checking out the board at component level. Like I
said,
I was just seeing if I can get all my ducks in a row beforehand to make
life
a little easier. Thanks again folks.

Cheers,
Lawrence



Oh boy, the days when I could spot a bad joint at 100 paces ... I'm lucky
now to be able to spot one at 100mm without my specs !!

Sometimes, when these jokers sand the tops off of ICs, they don't do a very
good job. On many occasions, I've been able to recover at least a partial
number by moistening my finger tip, and just wiping it across the top of the
IC, whilst shining a strong light at it. Sometimes, something more oily does
the trick. Worth a try.

Arfa

Thanks for the reminder. In the past I have used a bit of mineral oil or
instrument oil for flight instruments (I am a flight simulator tech) to brighten
the chip markings so they were easier to read. It is rare that I come across
sanded chips so I had forgotten all about that until your mention of something
oily. Thanks again.

Cheers,
Lawrence

Arfa Daily wrote:

Sometimes, when these jokers sand the tops off of ICs, they don't do a very
good job. On many occasions, I've been able to recover at least a partial
number by moistening my finger tip, and just wiping it across the top of the
IC, whilst shining a strong light at it. Sometimes, something more oily does
the trick. Worth a try.

Arfa

Here's my update and simple fix for the problem. Initially I was just shown
the speed control board just to see if I would be willing to have a go at
it. This is why I was looking for access to a schematic out there. Anyway, I
said sure so the person brought me the whole saw. I popped open the switch
panel on the saw and found a wiring problem so it turned out to not be the
control board after all. It seems the owner was cutting something and the
saw popped its lock. The owner reset it and it popped again. The owner
thought it might be something happening behind the switch panel so he popped
it open. In the process he accidentally switched one of the wires going to
the power switch with one of the wires going to the light bulb switch. At
this point the saw wouldn't work at all when he switched it on. Thank God he
had only switched the two wires he did. If he had switched any other wires
he would have had a pretty loud bang when he tried to power the saw on since
he would have created a dead short in the AC line and it probably would have
knocked him ass over teakettle. Anyway, I swapped the wires back to where
they should be and everything was good again in a matter of a couple of
minutes.
I know some people take offence when they ask a question and have other
people tell them to keep their noses out of it or they might get hurt. Most
times I don't think the ones saying to stay out if not experienced are being
cruel or anything like that. They are just trying to help prevent someone
from getting seriously injured. So, if you are reading this and you don't
consider yourself to be experienced in repairs then please take the time to
seek good help before tackling what may appear to be a simple task yourself.
The fingers you save just might be your own.

Cheers,
Lawrence