Berninas really are the best sewing machines ever made, and are certainly the best central bobbin machines by far. They are quieter, smoother and more reliable than any other CB I've ever seen.
The 830 and other 8xx machines are the best of the best, but the 730 and other 7xx machines are pretty much the same. As with all machines, they have their issues. The one that springs to mind for all of these is the camstack gear, which Bernina decided was best made from nylon. Nylon was a good choiceover what they used before that (midway through the 530 they swapped from a more reliable plastic) but as most of us know, after about 40 years they crack and have to be replaced. Replacement is relatively easy and inexpensive (although you need to pick a good quality one - they're not all well made) and this has been documented quite well.
I will instead be going over the two more common issues I see in my shop.
1. The needle position won't move or can move too easily, and
2. The buttonhole mechanism will not move.
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| Both seized components are here |
The solution to both of these is not too complicated. Regardless of whether you have one or both of these issues, repair involves the same procedure.
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| The four important components for this job |
You must set the zig-zag control to maximum then remove the needle position knob. To do this, loosen the nut marked with a red 1.
Remove the knob by twisting and pulling at the same time. Note that there is a large spring washer on the front, between the knob and the machine body. The internal mechanism (marked 3) can be allowed to drop out of the way.
Next, loosen slightly the screw marked with a red 2. You should now be able to remove the zig-zag control which contains the buttonhole mechanism, which is a zig-zag limiter.
If you're doing this because you're having trouble with the needle position you won't be able to remove the plunger (marked 4), but if by some miracle it moves freely, remove the plunger as well as the spring behind it.
Assuming the plunger is seized, you need to turn your attention to the front. Remove the three screws that are holding the zig-zag label on. It is also holding the plunger and spring. Once you have removed this, carefully remove everything. If you might not remember where everything goes, take pictures with your phone.
With everything out, you need to apply some heat to the seized component/s to loosen them Don't be tempted to force anything with tools. Remove the spring before you start.
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| Components in boiling water |
Put the zig-zag control and the needle stop into a cup and pour very hot or boiling water into the cup, covering the parts. Wait for a couple of minutes then remove the parts one at a time. The buttonhole mechanism should now be soft enough that you can move it with your hands. Apply some solvent if it starts to move (methylated spirits and mineral turperntine), and move it back and forth. After several of these, it should be very easy to move and you will start hearing a click when it goes back and forth. Now, dry it (I use compressed air) then apply a drop or two of SMO (sewing machine oil) and work it in. Pat yourself on the back because that's one job done.
Remove the plunger and use your bench to try and push the plunger into the housing. Once you can do this, apply solvents and use something reasonable strong and pointed to pus it out again. Once it gives a little, the solvent makes it much easier very quickly. Again, apply a drop of SMO, work it in, and reassemble.
Reassembly is actually pretty easy. You can put the spring and plunger in after the housing, because it's no longer stuck. Be careful not to lose the spring.
Make sure you have the spring washer on and push the zig-zag control before tightening the screw. Setting the zig-zag in the right spot is made easy because the mechanism needs to be at the bottom of its travel at the zero setting. If you have chosen to put the spring and plunger in afterthe zig-zag control, do it now. The part marked 3 can now be replaced and tightened and you're finished. If you find it hard to set the zig-zag and needle position, loosen it off just enough for an adjustment.
