Repairing a Bernina Record 730

Found a Bernina Record 730 at a junk shop, completely seized with a cut cord but it came with the foot pedal, accessory box and…oddly…a Record 830 knee lifter. Which I still have, and don’t really know what to do with. Of course I bought it right away. I was very excited. I have a very exciting life.

The brand, Bernina

Bernina is the cream of the crop when it comes to sewing machines, during the middle of the 20th Century, the three brands anyone wanted were Bernina, Elna and Husqvarna (Viking). Other brands were good, but not as, or cheaper. This has been switched up a bit over time, for example Elna started to die at the end of the century, and released a few garbage models, then were bought out by Janome, Pfaff built up etc etc. But Bernina remained at the top.

For most of the century sewing machines were fully mechanical devices, of course, and those three brands made full metal, heavy duty devices that did the job, did the job well, and would do the job forever with minimal maintenance. They really are works of art some of these machines (both figuratively and literally, the Elna Lotus can be found in the Museum of Modern Art) and when you pull them apart (easily) and need to make minor adjustments. For the most part, a bit of oil can fix most problems. A lot of thought went into making machines that would last the test of time, and that everyday users could maintain. A nice thought when compared to devices of today.

As a result of this, even today, 50 year old machines are still desirable for everyday usage and can command significant price premiums. Imagine people seeking a 50 year old computer for everyday work rather than hobby value.

The model, Record 730

Within the stack of Bernina models, the most well known are the Record series, which encompass the “30” family, eg the Record 530, 730, 830, 930, 1030. The “40” family are the Favorits and some “50”s exist which are Industrial models. Underneath the 30 models were a range of whatever flavour they wanted at the time. For example the 708 was basically a 730 without all the stitch patterns, and the 817 was a flatbed version of the 807. The 1000 series had things like the 1000 Plus (A 1010 with a Rotary Hook), the 1005, the 1008, the 1010 and a range of others to fill out their product stack. The Records all had a reciprocating vertical hook.

Generally (but not always, such as the case of the 1000 Plus) the higher the number the higher the status of the model.

The Record 730 specifically, was the last of the full metal models, but was otherwise almost internally identical to the 830. The 830 is generally the more desirable model, but I’d personally put that down to nostalgia of it being the new modern look when people who are now looking for Bernina’s were young.

To me, the 730, being internally similar but with a full metal casing that doesn’t age is more desirable.

Despite it being described as full metal, there were a couple nylon “sacrificial” gears that were intentional points of failure, better the devil you know. But in a twist of irony, the plastic degrades over time and eventually breaks through regular usage. And one of these gears has failed on this machine.

This machine itself

This machine itself, though, is an otherwise excellent condition piece with the 75th Anniversary Special Edition Badge, which makes it easy to date as a 1968 model. At the time of purchase I wasn’t exactly sure what the issues were at time of purchase, aside from it having a cut cord but I assumed whatever issues it had I could resolve.

The accessory tray was present, with feet and some needles. And, as mentioned earlier, a knee lifter which I later discovered was for a Record 830, and not this machine. The presser foot was the comfortable larger version that came with the Special Edition model and could be secured to a table if desired.

Once I was able to get it home I was able to start inspecting it closer, most of the knobs moved happily, and the needle responded.

The First Problem – Cut Cord

But of course the cord was completely cut off which usually signifies an electrical problem, which I expected would be a failed motor or something, or maybe something shorting. In any case it shouldn’t be a wildly difficult fix as the only electrical parts are the foot pedal and motor.

The Fix – New Plug

I started by simply chucking a new plug on the end of the cord, a simple task and something everyone should know how to do, great for fixing frayed cords, or devices you’ve bought overseas with overseas plugs that you’re constantly swapping adapters on. I’ll write and link an article here soon about doing it if you don’t already know.

Warning: There is electrical risk in doing this, the cord was cut for a reason but I’m confident in my knowledge of the circuit that I believe at most we’ll get a short and blow a breaker, or that it will go to ground. In any case I won’t be touching bare metal with my hands until I know it’s safe. Fire risk is very low as long as I’m present.

The device is hooked up to a 10a power board with a breaker, and the main 16a breaker at the wall if something goes wrong. It’s not an ideal scenario but I think it should be good enough. Cord on, press the pedal and the motor buzzes but doesn’t move.

Good sign, it’s getting power, the pedal is feeding it and nothing out of the ordinary. I believe that it should now be relatively safe, and that the cord was cut because the motor wasn’t doing anything but buzzing.

Buzzing could be a couple things, the most likely culprit on a device of this age is a blown start capacitor, AC motors have a capacitor which fires a pulse out of sync to get the motor moving, wherein the standard current can then take over.

I disengage the motor from the drive by spinning the knob on the drive wheel (all sewing machines from my knowledge have this ability) and press the pedal, motor fires up without any difficulty whatsoever. Speed control all works and it’s good.

So it turns out the motor and electrical system was fine, the electrical tester probably wasn’t aware of the ability to disengage the motor, so concluded the motor capacitor was fried and cut the cord.

Fixed, with minimal effort because it was never really broken in the first place.

The Second Problem – Seized Machine

Of course this leads to the second problem, the machine buzzes when the motor is engaged because the machine is absolutely seized and rock solid. It moves in either direction about 0.1mm. Some of the knobs and levels still work, but they’re not really engaged with the primary drive and any of the components (or several) could be causing the seizure.

Therein lines its own problem, how can you tell if you’ve fixed one, if others don’t allow the first one to move? So how you can tell which one(s) is/are seized to fix in the first place if there’s no movement?

The Fix – Brute Force

The first thought, of course, is “You can’t” and you consider pulling the whole thing apart bit by bit. But you really do not want to do that. As well as probably pulling it back together wrong, every component is timed and should activate at certain points. Pulling apart would make finding the seizure easy, but open a whole host of new problems.

Luckily there is a simpler method, as long as you’re aware of what would cause the fault in the first place.

Old oil, when left to sit for years, eventually turns to varnish. What this means is that, at least with old sewing machines, there’s very little that can cause a mechanical seizure, especially not one that can entirely stop the machine with no give in either direction, and the fix is what you’re always told not to do to fix stuff, brute force. The oil has basically just become glue joining the gears and you have to break those bonds.

In this case I absolutely loaded every metal to metal part I could find with oil, and every couple hours for two days would crank it as hard as I could using my hands only both ways. As the oil soaked in, and force was applied to damage the higher layers, on the second day it just came free like magic and happily cranked away.

One thing to note is that the whole process is very demoralising, as there’s no indication that it’s working, and you spend the whole time wondering whether you’re just wasting your time.

As a final note, acetone (or petrol) can speed this process up, as it thins out the varnish. However I didn’t take this approach as it’s difficult to get out afterwards and can damage the paint, and plastic and any other oil derivative components inside the machine.

Fixed with brute force.

The Third Problem – Stops Halfway

So, why did it seize if it takes years for the oil to turn to varnish?

The answer to that question is the third problem. It turns out there was an actual fault, and it was broken. And due to this break, the previous owner must have put the machine away intending to get it fixed. Fast forward many years and it was now not only broken, but seized. So they gave up and got rid of it. The business that got it came along and did an electrical test and heard the buzz, and cut the cord. Then it went up on the shelf at a low price as-is, whereupon I stumbled across it.

So there is an actual fault, and it’s the root of all the subsequent faults. As the machine turned freely, it was all fine and dandy until suddenly it wasn’t and it seized up. This occurred both by hand and using the motor. But unlike the earlier seize, I could run it in reverse and it would happily back up.

So somewhere along the process there was a single point on one of its functions that couldn’t move and unfortunately this once again becomes a prior knowledge thing although it’s now prior knowledge that you yourself will have.

If something breaks on one of these machines, it’s probably one of the gears mentioned earlier.

They’re made to break, they’re weaker than everything else so that if someone else gets into a situation where it could break, then this will break instead. Unfortunately due to the nature of plastic, it degrades over time and they end up breaking more frequently than they should. However, as they’re made to break, they’re also made to be fixed and so it becomes a standard job to repair.

If you open the top, there are two obvious plastic gears which stand out from the rest, these are your gears to check. The vertical shaft gear is dead-easy to inspect as it’s all there on show, but the cam stack gear which controls the built in stitch patterns is less obvious, and that was what was broken on this machine.

The gear looks like this, and there are two points where the breakage will occur which are the two visible holes below the splines. Upon winding the machine back, the slow moving gear eventually revealed a gap where a spline should be and that was the fault.

The Fix – Replace Gear

Now, conveniently, a Bernina technician named Neal Iuan made a series of excellent videos on how to fix Bernina machines, and I followed his video, shown below.

The steps followed on

  • breaking the gear off,
  • removing the pattern indicator,
  • removing the cam stack
  • giving it a good clean
  • putting it all back
  • timing the machine

I’m not going to go into detail on these steps as the detail is right there above. I will note, though, that he correctly spends a good portion of the video clearly detailing the size range that the aftermarket Chinese cam stack gears came in, which are usually slightly smaller than they should be which can cause a knock when running. Wherein they should be 37.7mm, but are often 37.2-37.5mm.

I ended up purchasing an aftermarket Chinese cam stack gear after sifting through the options on AliExpress because I couldn’t find one anywhere else that wasn’t an aftermarket Chinese one. However I took his information seriously, and conveniently some of the sellers had photos of their gears inside some callipers. There were none that were exactly 37.7mm so I chose one slightly oversized at 38.1mm (the rest were undersized) and when it arrived it was exactly 37.7mm. Go figure, I’m guessing I lucked out.

I replaced the gear, fired it up and everything ran beautifully.

Fixed by replacing the cam stack gear.


Honestly, it’s been a lot of fun fixing this machine. There were moments where everything worked out better than I hoped and demoralising moments where I felt like it was never going to work but I’ve since learned a lot about these machines and love the mechanics.

The machine really is a great model, and the full metal body means no mismatched colouring on yellowed casing (like you’ll see on the Kenwood Chef A901 that I’ll later write an article for

The machine now runs beautifully with no known faults. I’ve cleaned it up, taken some glamour shots that I’ll keep in my collection and eventually put it up for sale and on to my next project.

Keep an eye out for these, they’re fun to fix, the mechanics are amazing and the difficulty level isn’t too high.

…Oh and they’re excellent sewing machines, which is probably important (but not to me).

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