I love our vintage machines I really do but sometimes they drive me mad
I picked up a 63 Alu 201k in very good condition, remarkable condition actually. Having done the usual wiring checks I plugged it in and what a racket!!!
The motor induction noise and the foot pedal popping and fizzing lead me stripping them both down for inspection.
The motor was pretty clean but being a BAK 13-12 it is a noisy motor anyway. Induction whine on my test foot controller was still evident but nowhere near the level of the unit it came with and that lead me to the control unit within the pedal itself. Stripping it down and removing the "putty" or whatever it is that frees the threaded bars that in turn unlock the carbon / graphite disks I started the sripdown. There are 53 of these little round disks in each side with the thickest being at the bottom. That means cleaning 106 disks smaller than a half pence piece and half as thick. The way a foot pedal / motor contol works is via resistance. The carbon disks offer resistance thus slowing the speed of the motor, the upshot of resistance is heat and perhaps some noise. Panic not if your pedal gets warm, it's a genuine result of electricity. Anyhow, this pedal in particular was suffering. There was no flow through the depression of the button, it was all or nothing, very little in the graduated acceleration, slow, slow, quick, Holy Cow!
After stripping it and emptying the disks on to clean kitchen towel, one for each side. it became apparrent that all was not well. Both bottom (thickest) disks were broken as well as a total of 15 resistance disks. The noise I was hearing was electricity popping through and arching over the disks. The heat generated was due to additional resistance, half a disk alters the resistance and can induce arcing and as such increases the heat. This was the popping sound. Bear in mind that if yours does pop it doesn't mean that anything is wrong, that is just the heating and cooling process.
Finally, after cleaning every single disk and replacing the broken ones with clean replacements the pedal was reassembled. This in itself is a tricky aspect, explanion in another topic.
Plugged it all in and tested it on the noisy BAK and yes there was induction noise and hesitation but once plugged into the other machines it was glorious, so smooth and predictable, single stitch predictable. I still have fingers full of graphite as I write this, it's a dirty job and unless you want to endure a day of tedium I would just go find another pedal. If on the other hand you are like me and like to delve into the unseen parts, how they work and how to fix them then dive in, just dont do it on the kitchen table!
Barny