Sewing Machine Simulator

First of all, some words of warning:

It is absolutely mandatory to know what you're doing when repairing or tinkering with devices operating on mains voltage, no matter whether you do that in a 230 V or in a 115 V environment. Mains voltage can cause an electrical shock that is extremely unpleasant at best, but can kill you in the worst case!

ALWAYS disconnect the unit from the mains before touching anything inside it.

Remember: Learning by doing might be too slow!

I volunteer in the non-profit repair shop of a community centre, and from time to time a sewing machine is brought in. In some cases the owner has troubles operating the machine because she/he didn’t bother reading, understanding, or following the !#@&ing user's manual, and sometimes the machine just wasn’t sufficiently cared for. Older sewing machines in particular are marvels of precision mechanics, and as such they need some TLC (tender, loving care). Cleaning the accumulated fuzz and thread from the mechanics, plus the right amount of the right oil, in the right moment and in the right places (yes, there usually are lots of different lubrication spots hidden under the covers) is mandatory and can perform wonders – procedures that are, of course, covered by the respective user's manual.

If, however, there should be a problem with either the cable or the ‘gas pedal’ rather than with the machine itself, lugging the heavy machine to our shop for a repair or check-up isn’t necessary at all.

In fact, a sewing machine foot pedal is nothing but a mechanical or electronical light dimmer. There are a few little differences, because driving a sewing machine motor is a bit more demanding than dimming an incandescent lightbulb. Such a dimmer pedal can, as every other mechanical/electrical/electronical device, fail after years of use. Connecting cables, too, can be ailing after year- or even decade-long (ab)use.

Using an appropriate adapter allows troubleshooting a suspected cable/pedal assembly in (y)our workshop without lugging a heavy sewing machine around. Therefor I call this my ‘sewing machine simulator’.

Vintage electrical sewing machines from the 1960s (such as the venerable beauty that I inherited from my mom, see above) are equipped with the stone-age, mechanical rheostat that is enclosed in a ceramic case. It contains one or two columns of many thin (about 0.5 mm) graphite pills that have a high electrical contact resistance when in their relaxed rest position. The more pressure is exerted on them when pressing down on the pedal, the smaller the resistance becomes, and so more current can flow from the mains outlet, through the pedal, to the machine’s motor. The concept can work for decades, but generates heat in operation and is not too energy-efficient. This kind of pedal is still available today as a quite inexpensive (but perhaps not too long-lasting) replacement – provided you know how to connect it to the machine. These pedals only need a two-pole cable between machine and pedal.

Later machines came with more or less sophisticated, electronical pedals. Some of them need an additional, third, 'live' wire for supplying the electronics (identifiable by a three-wire cable or a three-pin connector), and most others doing without it (two-wire cable or two-pin connector). This kind of pedal as well is available as a quite inexpensive replacement; in order to connect such an aftermarket replacement pedal, the third (supply) wire can be left out – again, as long as you know how to connect it to the machine.

Unfortunately, most sewing machine manufacturers chose to design their own, specific connectors, not only for safety reasons but also for ulterior, commercial motives. Therefor, replacing a cable or a pedal is usually becoming more difficult the older the machine is, because these connectors are hardly available as spare parts, if at all, and often only complete with cable(s) and usually the pedal. Of course, the manufacturer would prefer selling a new machine to supplying a replacement pedal or even a replacement cable and/or connector. Even if a matching pedal and/or cable is available (or if you manage finding a second-hand replacement on an auction platform), this may become quite expensive. But, as already mentioned above, there are cheaper solutions available. I will mention some of these as well as my own DIY pedal, towards the end of this Instructable.

Please note: Recent machines, identifiable by a low-voltage pedal equipped with a plug similar to the one you know from your headphones, are NOT covered by this Instructable, because these machines have all the control electronics integrated inside their enclosure, if I understand correctly. Their pedals, as far as I know, only contain a low-voltage potentiometer. Once I should stumble upon such a machine, I might extend this Instructable accordingly.

In the following steps, I will show you how to identify and troubleshoot different cables/pedals of some of the popular (at least in my European region), earlier sewing machines, and how to cobble together makeshift adapters and connectors that allow simulating these machines, mostly with materials from your junk box, for next to nothing.

Please be aware of the fact that these makeshift adapters and connectors are exactly what their name says - makeshift, a.k.a. workaround, expedient, quick & dirty - and they might have, depending on your implementation, your skill level, and your safety awareness, a somewhat reduced safety standard. But they are intended for troubleshooting only and never for use over extended time periods.

Real-world cable and connector repairs are not the main focus of this Instructable, but I will mention one or two examples towards the end, just for your information, in case you should become curious.

Materials

1. Brass (preferred) or steel screws, e.g. M2 or M2.5, length about 20 mm – depending on the actual pedal/machine/cable combination, and/or
2. Pins harvested from an old IEC-320 appliance inlet – depending on the actual pedal/machine/cable combination
3. Perhaps two springy 4 mm ‘banana’ plugs from your junk box – depending on the actual pedal/machine/cable combination
4. An old (but working) 60 to 100 W incandescent lightbulb – yes, it has to be an incandescent bulb! You might use an 80 W, linear, halogen bulb instead, since they are still available nowadays (but I don’t know for how long)
5. A socket for the lightbulb or an appropriate socket for the linear halogen bulb. In case of a linear halogen bulb, you must provide a contraption that protects the user (you) from touching the halogen bulb, because in operation, they become VERY hot VERY fast, and you never! must touch them with your bare hands, even while being cold
6. Some two-pole stranded wire with a cross section not less than 0.5 mm²
7. Matching wire-end ferrules
8. Some PS (polystyrene) sheet, about 1 mm thick – perhaps pilfered from some packing material
9. Masking tape
10. Heat-shrink tube (may in a pinch be substituted by electrician’s tape; not recommended)
11. Chopsticks or other wooden sticks of matching size, such as skewers
12. Polystyrene cement (as used for assembling plastic model kits)
13. Hot glue sticks
14. Solder; easiest to solder with is the old-fashioned tin/lead alloy (63 % Sn, 37 % Pb) that unfortunately fell from grace due to its toxic lead content. It may, however, still be used for DIY and medical applications. The current, lead-free solders cannot be processed that easily, they require a somewhat higher soldering temperature and usually some more flux. Solder joints with these solders are, in addition, less reliable.

Tools

1. Ohmmeter (or a multi-meter with Ohms range)
2. Continuity tester
3. Small screwdriver
4. Scissors
5. Wire cutter
6. Wire stripper
7. Crimping tool for wire-end ferrules (optional)
8. Hot-glue gun
9. Hot-air gun
10. Soldering iron

The internal and external wiring of household sewing machines usually follows three different, basic configurations, of which I show you three example diagrams here. These diagrams are not too complicated and show the interconnection of mains, pedal, and motor, including the sewing light within the machine that can be switched on or off, independent of the motor control.

1. Bernina machines from around 1960 (e.g. the 530 Record pictured in the introduction, and the early 730 Record versions) have two separate, dual-wire cables. One of them connects the machine to the mains outlet. The connector in the machine is similar to today’s IEC-320 male appliance inlet but has two pins only. The second cable is fixed to the pedal, it connects to the machine with a proprietary, two-pin, male plug, see the ‘Version 1’ diagram. Since the two cables are separate, no more has to be said about them here.
2. Later Bernina 730 Record models from the late 1960s have a single cable that is kind of a daisy chain; two dual-wire cables are joined at the proprietary female connector that is plugged into the machine. One of these cables goes to the mains plug, the other one to the pedal. See the ‘Version 2’ diagram. For these machines, inexpensive aftermarket replacement pedals can be found that, with some luck, are even equipped with connector(s) matching the machine.
3. Bernina 830 Record versions (early 1970s) are similar, but the pedal cable has an additional, proprietary, female connector that plugs into the pedal. See the ‘Version 2’ diagram. For these machines, inexpensive aftermarket replacement pedals can be found that are even equipped with connectors matching the machine; if not, connecting them is no witchcraft as long as you know how to do it.
4. Then there were the Bernina 802-803 series machines that featured electronic pedals for the first time (afaik). These pedal cables had a third wire because the electronics within the pedal needs supply voltage. The cable itself is a daisy-chain configuration, too, with a proprietary female connector that looks as if it had four contacts, but only three of them are used. Two cables start there: A dual-wire cable that goes to the mains plug, and a triple-wire cable that plugs to the pedal, again, with a proprietary female connector. See the ‘Version 3’ diagram. Spoiler alert: Substituting such an original pedal by a modern replacement pedal that has a dual-wire cable only is possible without problems – the only thing you need to know is how to connect it.
5. I have one more cable/connector/pedal combination in my collection that fits a Singer 8280 sewing machine. It is much younger but still about 20 years old and seems to be very similar, if not identical, to the one I found on a ‘Durabase’ supermarket-brand machine of about the same age, if I remember correctly. This is as well a daisy-chain configuration, but with a different, proprietary female machine connector that, of course, doesn’t match any Bernina machine that I know of. The ‘Version 2’ diagram is valid for this connector type, too.
6. I will get access to a vintage, Swiss-made Keller sewing machine soon. When I have collected the information for its cable/connector/pedal, I will update this Instructable accordingly.

Update:

The Keller Kl.22 and Kl.2800 wiring is very similar to the 'Version 1' diagram above, with two little exceptions: Both two-wire cables (from the mains outlet to the machine, and from the machine to the pedal) are permanently fixed to the machine, and the pedal cable is plugged into the pedal with the same connector that is used for the connection of the mains cable to the Bernina 530 machine.

This might be somewhat confusing, but unless you have a Keller and a Bernina 530 machine side-by-side, it's unlikely that there is a mix-up.

Needless to say that the Keller pedal must NEVER be connected directly to the mains using a Bernina mains cable – otherwise, some fireworks and other nasty olfactory effects must be expected.

When comparing the diagrams of the three different versions in step 1, you can see that they are not that different.

To avoid misunderstandings: Please note that for detecting the pinout of the machine connector, only the cables and the pedal are required, but not the sewing machine.

Version 1 is the easiest to understand – there are two cables, one for connecting the machine to the mains outlet, and another one for connecting the pedal to the machine. The common conductor of the two cables connects via the machine, and there are, of course, two connectors, both of them with two contacts. The appliance inlet at the machine is male, and the plug on the cable from the pedal is male, too – so it is impossible to get zapped (or worse). In this case, nothing has to be detected because the two cables are clearly separated. And since we deal with AC (alternating current) here, there is no polarity to be observed.

Version 2 is almost identical, but the two cables – mains to machine, and pedal to machine – are combined at the single machine connector that has, now, three contacts. The common conductor of the two cables is connected within the machine connector rather than within the machine. There are different cases.

Regardless whether the pedal is mechanical or electronical, if there is an additional connector between pedal and pedal cable, it’s easy. You can find the contacts common to mains plug, machine connector and pedal connector with an ohmmeter or a continuity checker; the common contact at the machine connector is usually the centre contact.

In case of a mechanical pedal, if the pedal cable is fixed at the pedal, finding the common contact is not that simple. First, establish (using paper, pencil and a sketch of the connector’s front view) which two contacts of the machine connector are connected to the mains plug. Let’s assume the contacts #1 and #2 of the machine connector are connected to the two pins of the mains plug. Select the 1 kΩ or the 10 kΩ range on your ohmmeter and connect it between contacts #1 and #3 of the machine connector. If the resistance reading is infinity regardless of whether the pedal is pressed or not, contact #3 is not the common contact, but contact #2 is. If the ohmmeter reads between infinity (pedal not pressed) and some 10 to 20 Ω (pedal fully pressed), then contact #3 is the common contact. Usually, the centre contact, that is, contact #2, is common. To be sure, you might open the pedal carefully and check with the continuity checker which contact of the machine connector goes to both the mains plug and to the pedal. This will be the common contact.

Worst of all is an electronical pedal with a fixed cable – then you cannot use the ohmmeter but must try to open the pedal carefully, that is, non-destructively, and check with the continuity checker which contact of the machine connector goes to both the mains plug and to the pedal. This is the common contact.

Version 3 is almost identical with version 2, but the pedal cable has three conductors for supplying the pedal electronics. I never met a pedal requiring the additional supply with a fixed cable, but identifying the common and the supply contacts on the pedal connector isn’t easy nevertheless. For this purpose, you either have to guesstimate, use trial & error, and/or you need access to manufacturer’s specs (that I fortunately had during repair of the Bernina 286 pedal supplied with the Bernina 802 and 803 ‘electronic’ machines).

Provided that the manufacturer didn't change wire colours during production, the wires for connecting a dual-wire pedal are black and brown. The third, blue supply wire is no more used, and its end must be insulated.

To simulate the machine for checking pedal and cable(s), you need a connector (or connectors) similar to the one(s) installed in the machine. They must, of course, match the machine/pedal cable connector(s).

Unfortunately, these connectors are rarely available off the shelf or not at all, so you have to cobble them together by yourself. To make things easier, the simulator only needs two contacts, even if the machine connector has three contacts – with the exception of version 1 that needs both a two-pin ‘machine’ plug and a two-pin ‘pedal’ socket. As long as the whole thing remains well insulated and so electrically safe enough, it doesn't matter if it is just a workaround. It is intended for a short test only but not for long-term usage.

The two first pictures above show the connectors on my Bernina 530 Record machine with their matching plugs, first the connector at the rear of the machine that connects to the mains, then the one at the machine's right-hand side where the pedal cable is plugged in.

I will give you step-by-step instructions how I made the connectors for version 1. Some words about connectors for the other versions will follow.

First, the two-pin, male, machine plug:

1. You need the female machine connector (picture #3) and a strip of polystyrene about 2.5 cm wide, 1 mm thick and long enough to fit at least two times around the machine connector. Tightly wrap the polystyrene strip around the end of the machine connector and use polystyrene cement on a length of about 1 cm at the beginning of the strip. Clamp together until the cement has set.
2. Then coat the rest of the strip with glue and wrap the whole strip tightly; fix with some masking tape and clamp until the cement has set (picture #4). You can then pull this coil away from the machine connector, it will be the collar of your new plug substitute.
3. Cut up an old IEC-320 appliance inlet (picture #5) to remove its pins (picture #6).
4. Strip the ends of a piece of two-wire cable, tin them and solder them to the two shorter pins (picture #7).
5. Cover the ‘business end’ of the machine connector with masking tape and cut it to shape. With a knife cut two slots into the tape where the pins will go in (picture #8). Thanks to the masking tape, the machine connector used as a template and the new plug will be easier to separate later.
6. Slide the polystyrene collar over the end of the machine connector so that it protrudes about 10 to 15 mm over the end of the connector. Firmly push the two pins with the connected cable into the two slots (picture #9).
7. Fill the hollow within the polystyrene collar and cover the ends of the pins with hot glue, then let it cool down (picture #10). Only after it has cooled down completely you can separate your new connector from the machine connector – which normally requires some patience and/or gentle violence.
8. You may want to slide some large heat-shrink tube over the polystyrene collar that extends towards the rear. Shrink it with your hot-air gun. Once it has cooled down, fill the gap between the cable and the end of the heat-shrink tube with some more hot glue as a kind of makeshift strain relief (picture #11).

Then, the two-pin, female, pedal socket:

1. The pedal plug has two pins with a diameter of 4 mm (picture #12). To contact these, I used two old, hollow ‘banana’ lab plugs by ‘Stäubli MultiContact’ that are springy enough to accommodate and reliably connect to the 4 mm pins of the pedal plug (picture #13).
2. Strip the ends of a piece of two-wire cable and solder them to the end of the two lab plugs (picture #14).
3. Cover the front of the pedal plug with masking tape (picture #15).
4. Plug the two lab plugs with the cable end onto the pedal plug (picture #14 again).
5. Put a piece of tube with sufficient diameter over the lab plugs and temporarily tape it to the pedal plug (no picture for that step, sorry). This tube piece must be somewhat heat resistant because it will be filled with hot glue; I used the inner cylinder of a roll of adhesive tape and didn’t check for thermal stability in advance; after filling it with hot glue it immediately went soft and shrank faster than I could watch – not so good (picture #16).
6. Fill with hot glue and let cool down. My ‘socket’ was really ugly and smaller than planned (picture #17).
7. Slide some heat-shrink tube over the assembly and shrink it with your hot-air gun. Again fill the end of the heat-shrink tube with hot glue as a kind of makeshift strain relief (picture #18).

For producing (male) connectors matching (female) machine connectors, some imagination and improvisation is required. The principle is similar to what I told you above: Use the cable’s (female) machine connector as a template and find matching contacts. I used instance pins harvested from old, cut-up IEC-320 appliance inlets, but in some cases also screws with a matching diameter, M2 and M2.5 in two cases; the cable can be connected by soldering or by using solder lugs fixed to the screws with a nut and perhaps one or two serrated washers.

Most of these connectors have special outlines and also recesses that protect them from being plugged the wrong way round, and these must be modelled as well. I again used polystyrene sheet for the collar, and the smaller ends of chopsticks to fill in the recesses. To mechanically fix and at the same time electrically insulate the pins and the chopstick ends, I recommend hot glue here as well. You will find pictures of some of these connectors from my collection a little later.

The Keller two-pole, female pedal connector mentioned in the update at the end of Step 1 is shown at the left in picture #19 above; it is identical to the one at the machine end of the Bernina mains cable. The black, three-pole version with additional, protective earth contacts at the right has been used e.g. for coffee makers. I don't know if these connectors have been used internationally, but they were popular in Switzerland at the time.

BTW, the two-pole mains cable with the female connector mentioned here can be, in a pinch, replaced by a mains cable with an IEC320/C9 female connector. These cables have been used for many years with Revox HiFi and some Roland equipment. Their female connectors differ by having a slightly smaller outline, but the contact configuration is very similar to the one known from Bernina and Keller.

The heavy lifting was done in the last step, it gets easier now. Let’s continue with the example from step 3, with two separate cables for the machine and the pedal connectors, also refer to the ‘Version 1’ circuit diagram above.

1. You have two short pieces of cable with the new custom connectors on one end, the other ends still are free. Strip both ends, twist one wire of each cable (in my example, the blue wires) together, and solder (picture #2 above). The two other ends should be provided with wire-end ferrules – if you closely watch the picture, you can see that the brown wire ends are not soldered. There exist tools for crimping wire-end ferruless, but don’t worry if you don’t have one. You can also give them a few gentle nicks with your wire cutter, because they just should be fixed a little on the wire until they are clamped in the simulator's screw terminal.
2. Bend the two (blue) connected wires backwards and insulate the soldered end with a bit of heat-shrink tube (pictures #3 and #4).
3. Connect the remaining (brown) wire ends of your cable assembly to a bulb socket (picture #5).
4. Fill the gap where your cable assembly enters the bulb socket with some hot glue as a kind of makeshift strain relief (picture #6).

Tadaa, you’re done!

You can now test pedal and cables with your new simulator – just connect first the pedal cable to your custom female connector, then the machine cable to your custom male connector, insert a lightbulb (60 to 75 W) into the socket, and finally plug the other end of the machine cable into a wall outlet.

If the cables and the pedal are ok, you can turn the lightbulb on/off and dim it using the pedal, as shown in the video below.

If the pedal is faulty, there are several possibilities:

1. The simulator’s lightbulb is always ON, regardless if the pedal is pressed or not. In this case, when plugging the cables to the machine instead of to the simulator, the machine immediately starts running at full throttle – then most likely the capacitor in the mechanical pedal must be replaced. It is also possible that the pedal produces a nasty smell, gets very hot or starts to smoke. If the capacitor isn’t the culprit, then I recommend replacing the pedal, see step 5. Please note that when using a mechanical pedal for an extended time, also in normal operation it can become warm, but it will not produce any smoke signals or other olfactory effects.
2. The simulator’s lightbulb is always OFF, regardless if the pedal is pressed or not. In this case, when plugging the cables to the machine instead of to the simulator, the machine will not run regardless of the pressure on the pedal – then most likely the pedal is faulty. Faulty pedals can be repaired, but it is a bit tricky; in such a case I recommend replacing the pedal, see step 5.
3. The simulator’s lightbulb is sometimes ON and sometimes OFF when moving the cable(s) around while the pedal is pressed. In this case, when connecting the cables to the machine instead of to the simulator, the machine will sometimes run, or stutter, and sometimes it won’t – then most likely somewhere along the cable’s length there is an interrupted wire, usually close to one of the connectors. You can try to locate the interruption by intentionally wiggling the cable while pressing the pedal. For repairing interrupted cables, see step 6.

There also could be a slack joint inside the pedal, in its mechanics, or its graphite column. However, repairing pedals is a bit beyond the scope of this Instructable; in such a case I recommend replacing the pedal, see step 5.

The not-so-very-different diagrams for machine simulators of the version 2 and 3 types are given above, too, followed by a picture of some more DIY connectors and simulators from my own production for different sewing machines, from left-to-right:

1. The simulator for 530- and early 730-type Bernina machines. This is the one for which I gave the step-by-step instructions in step 3 above.
2. The simulator for later 730-type Berninas.
3. The simulator for 802/803-type Berninas (this is first one I made, and as you easily can see, it's the ugliest of them all).
4. A little off-topic: Adapter for connecting an aftermarket pedal to the pedal cable connector of the 802/803-type Berninas. In fact, only two of the three pins of the adapter plug are used.
5. And the last one at the far right, again a little off-topic: Simulator for a Singer 8280.

This is my little family of sewing machine pedals – from left to right:

1. The mechanical LWA-43/2 pedal for the early Bernina 530 Record, Swiss-made by Scintilla SA. I think also the early Bernina motors were provided by Scintilla.
2. A more modern, cheap, mechanical ‘horseshoe’-shaped pedal (https://www.amazon.de/N%C3%A4hmaschinen-Fu%C3%9Fpedal-Hufeisenf%C3%B6rmiges-EU-Stecker-Universeller-Empfindlicher/dp/B0CDHZW4BZ/ref=pd_ci_mcx_mh_mcx_views_1_image). There are several retailers selling via Amazon, but the machine connector of none of them matches any Bernina machine – so you have to connect the cable from the pedal to your original Bernina pedal cable by yourself.
3. A modern, cheap electronical pedal (https://www.amazon.de/ckpsms-Marke-325-213-14-FUSSBEDIENPEDAL-N%C3%A4hmaschine-830-831-800/dp/B07YD1GJM9/ref=sr_1_7?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&sr=8-7). There are even versions with a machine connector fitting the Bernina 830-series sewing machines. You can, however, connect the cable from the pedal to your original Bernina pedal cable by yourself if you have a different type of machine.
4. And the one at the far right is my own, DIY sewing machine pedal. I made it using a Proel GF12L guitar volume pedal. It contains nothing but a potentiometer and a very simple, very convenient dimmer module by Conrad. But at the end of the day all the components cost me more time and money than any of the two replacement pedals above.

These pedals all are specified for 220/230 V mains voltage. If you live in a 110/115 V country, be careful to purchase a replacement matching your local mains voltage. The two links above are, of course, only valid at the time of writing, they can be dead tomorrow or the day after. But I'm confident that you know how to use Amazon's search function.

When buying a replacement pedal from Amazon or, e.g., AliExpress, make sure that you really get what you want before you click on the 'buy' button! Many sellers, not only from China, either don’t really know what they sell, or they trip over the language barrier – the amount of nonsense you can find in many of the product descriptions is amazing. So, caveat emptor! (in plain English: Buyer beware!). Sending back an item that doesn’t really match and getting a refund is rather easy with Amazon, but very difficult if not impossible with a Chinese seller – and shipping to China can become quite expensive, at that.

Connecting the two-wire cable from the pedal to the sewing machine’s original pedal cable is no rocket science – except in the case of the three-wire, version 3, pedal cable. There you have to be careful to pick the two correct wires for the connection - one helpful hint to do so is given at the end of step 2. When connecting (‘splicing’) cables, make sure that the contact is mechanically solid (e.g. by tightly twisting the two wire ends together before soldering), and that the two wires are insulated from each other and from the outside world, e.g. by using heat-shrink tube.

This step is not exactly the main focus of this Instructable and is work in progress, I apologise for that. It will be updated step by step, as soon as it is finished. Thanks for your patience!

When the simulator’s lightbulb is sometimes ON, sometimes OFF when moving the cable(s) around while the pedal is pressed, or the machine will sometimes run, or stutter, and sometimes it won’t, then most likely there is a broken wire somewhere along the cable’s length. Take your time to locate the interruption by intentionally wiggling the cable while pressing the pedal. These interruptions occur close to a connector in most cases.

Repairing the cable can be difficult, depending on the connector

(to be continued)