2024-06-29 - Fixing the Starter on an Old Sewing Machine
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WARNING: All the standard warnings apply. In particular, unplug
everything before working on the electrical parts of the sewing
machine.

WARNING: I'm not an electrician, so take everything here with a grain
of salt.

A while ago, I decided to take a closer look at my grandparents'
old Pfaff 260 Automatic sewing machine[0]. This sewing machine mainly
worked as it should, the only problem was the starter[1], activated by
a foot pedal. The problem was that there were essentially two speeds,
on and off, which made sewing with it quite difficult. I first tried to
fix the starter, but eventually decided to get a different one. I still
want to mention a few important parts of the disassembly/reassembly
in case anyone else wants to attempt that.

WARNING: The starter on this type of sewing machine is directly
connected to mains voltage, so be very careful when working on it.

First, the piece connecting the starter to the foot pedal needs to be
unscrewed from the foot pedal[2]. Then, the actual starter can be
taken apart. I performed this disassembly almost half a year ago, so
I don't remember everything, I just know that quite a few screws
needed to be removed, and the lever activating the mechanism also had
to be removed first (the spring holding it up can just be unhooked
from the frame). There also is padding around some screws that can
easily fall out, so make sure you remember where that goes. Once the
starter is open, the mechanism can be seen[3]. The way it works is
that there are some sort of carbon plates which are pressed together
by the lever mechanism, causing the resistance to drop[4]. As can be
seen in [3], there is also a regular contact piece in the middle that
eventually bridges the contacts directly without going through the
carbon plates. If the resistance of the carbon plates is too high
even when they are pressed together, electricity will only flow once
the contacts are bridged in the middle, essentially making it an
on-off switch. In this case, the plates at the very end were
completely corroded[5]. I removed the completely corroded plates,
cleaned the other parts, and put everything back together.

One more note is that the contact piece in the middle can be
adjusted[6] so it is further away from the contacts, meaning that
they are only bridged after the carbon plates have been compressed
further. Of course, if it's too far away, the contacts may never be
bridged, which would also be an issue.

The reassembly is very annoying because the screws need to go into the
right holes while at the same time, the part that the lever is later
attached to needs to be pushed against the force of a strong spring so
it also goes in the right hole. It works best to stick a screwdriver
through the hole in the case where the lever is attached so it can
be used to push the part inside against the force of the spring. I
noticed one design "feature" where the filter capacitor is located[7].
There is a long screw in each of the four corners. Three of them are
regular screws, but one of them only has a winding going about half
the way, with the rest of the screw just being smooth. This screw
needs to be in the corner with the filter capacitor because the smooth
part presses against the capacitor. This could have easily been
avoided by either making the case just a tiny bit bigger or by moving
the capacitor away from the screw. The latter option isn't possible
now because the capacitor is held in place by a screwed-down holder.
The holder can be rotated a bit, but I'm pretty sure I tried that and
it didn't make it any better. Maybe this is what they call German
Engineering. I guess it would probably be a good idea to replace the
capacitor with a proper modern safety capacitor anyways, but I ended
up getting a new starter, so it doesn't really matter.

After I went through this ordeal, the starter worked slightly better,
but it was still very difficult to get any speed between off and
full speed, so I decided to get a completely new starter. Another
option could have been to replace the carbon plates, but it seems to
be fairly difficult to get those at a reasonable price. I couldn't
find any starters of the same type (other than used ones for way too
much money), but there are plenty of cheap foot pedal controllers
you can buy. I got one with the model number YDK YC-190 for about
20€. It would have been ideal to get a separate power cable and
connect that to the new starter, but this sewing machine uses an old
Pfaff-specific power plug[8] that you can only get used for way too
much money, so I decided to cut apart the original power cable.

I decided to make the old and new starter swappable, so I attached
standard IEC 60320 C13/C14 connectors[9] to the cables. One important
note here is that the cable on the side of the starter should have
the inlet (i.e. C14, with the exposed pins). The cable coming from the
sewing machine has live mains power running across it, so there should
not be any exposed pins on that side. [10] shows the inlet for the old
starter. Note that the grounding wire in the middle should be a bit
longer than the other wires as an additional safety mechanism so it
tears after the other wires in case they are torn out. The new starter
didn't have a grounding connection, so the middle pin on its inlet
could just be left without any connected wire. Finally, a connector
had to be attached to the cable coming from the sewing machine.

The connections inside the new starter were made using the clamps
that came with it[11]. There was also some extra insulation that
could be added around the connections[12]. After all that work, I was
left with two interchangeable starters[13], although I don't know why
anyone would want to use the old starter anymore. [14] shows a short
demo of the new starter. On this sewing machine stand, it's actually
possible to optionally attach a wheel to the original foot pedal so
the machine can be operated without electricity. It might be a good
idea to connect that wheel so the original foot pedal can be used
for operating without electricity, while the new starter can still
easily be attached if electricity should be used. For now, though,
I'm just happy that the sewing machine can be used normally again.


[0] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/sewing_machine.jpg
[1] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/old_starter.jpg
[2] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/pedal_connection.jpg
[3] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/old_starter_mechanism.jpg
[4] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/ceramic_piece_plates.jpg
[5] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/bad_plates.jpg
[6] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/contact_adjustment.jpg
[7] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/capacitor.jpg
[8] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/plug.jpg
[9] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/connectors.jpg
[10] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/old_starter_inlet.jpg
[11] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/new_starter_clamp.jpg
[12] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/new_starter_wiring.jpg
[13] gopher://lumidify.org/I/phlog/2024-06-29-sewing-machine/new_starter_connected.jpg
[14] gopher://lumidify.org/9/phlog/2024-06-29-sewing-machine/demo.ogv