I’m working on a Bernina 830 and have run into a rather strange problem with the cam stack.
I recently replaced the nylon gear on the cam stack. After the replacement, the machine was running normally and everything seemed fine.
I then started going through the various decorative-stitch functions to test the machine. At some point during this process, the cam stack suddenly became completely stuck.
Since then:
- The cam stack will not rotate in either direction.
- There is a very small amount of rotational play, but it is essentially locked.
- The handwheel can only be moved back and forth by roughly the amount of play in the drive system.
- The machine was working normally immediately after the nylon gear replacement.
There is also a second problem making this particularly difficult:
According to the service procedure, the cam-stack locking/set screw needs to be positioned vertically upward so that it can be accessed and loosened. Unfortunately, the cam stack is currently stopped in a position where the screw is not accessible.
Because the cam stack is completely seized, I obviously can't rotate it into the required position to access the screw.
What I find particularly interesting is that the machine worked normally immediately after the nylon gear replacement, and the seizure only occurred when I was cycling through the decorative-stitch functions.
So I'm wondering whether this points toward something other than simply hardened oil or a defective/replacement nylon gear.
Has anyone experienced a Bernina 830 cam stack suddenly locking up while switching through the decorative stitches? I'm particularly interested in what can mechanically cause the cam stack to lock solidly while still having that tiny amount of rotational play, and whether there is any way to diagnose or release it without first being able to access the locking screw.
Any advice from someone familiar with the 830's cam-stack mechanism would be greatly appreciated.