Bernina Foot Pedal | Bernina Foot Control | Vintage Bernina Speed Regulator

The control pedal for Bernina sewing machines is a slightly older model of the pedal, but in terms of quality it lags behind the newer models, on the contrary, I think that these older ones are longer and more durable, so let's start in some order. On the desktop, in addition to the pedal, there is also a Bernina electric motor, the data on the plates are as follows: Bernina motor type 807/85 W, pedal: Bernina sewing machine speed regulator type 200, rated resistance 700 ohms. In our country, the usual name is "slipper", I am .....
I call it a "control pedal" and the English translation would be something like a "sewing machine speed regulator".
The pedal is connected to Bernina's electric motor for checking, pressing the pedal does not start the motor, the small "curtain" of foil does not start (1). I intended to open the pedal, regardless of the fact that it does not necessarily mean that it is defective, there are few posts on the Internet that deal with Bernina starting pedal, let me emphasize immediately, this post is educational in nature
this type can be performed EXCLUSIVELY by professionals, DANGER of electric shock. !! And those of us who work on this can be "struck" by electricity every day, most often it happens when turning the device on and off from the socket and during work, at times it is forgotten that the device is energized and that can be dangerous. !!! First and foremost is to disconnect the main line completely (2), there are 6 small screws on the underside of the pedal that need to be unscrewed and then set aside, then we remove the cover (3) and have an overview of the inside,
everything looks pretty clean, without any special traces of burning, on the left side is a capacitor, at first glance correct, usually, if it is defective it has a bigger or smaller crack on it, we see two slightly stronger springs that I removed but not necessary . In order to test the correctness of the pedal, this can also be done with an OM meter, the starting pedal is practically a switch of variable output voltage. The rated resistance on the pedal is 700 Ohms, that is the maximum resistance and
its reading is at the first contact inside the pedal, with increasing pressure on the pedal the resistance decreases and thus on the machine motor comes a higher voltage and an increase in the speed of the electric motor (4). Figure 5, why am I emphasizing it, I will use it to try to explain the principle of operation of this pedal, of course it is easy for those who understand electricity, but for a layman I am not sure ,? So two wires are the input to the pedal and basically it's one wire through which voltage is passed through the electrical circuit inside the pedal, say on 
half the pressure of the pedal input voltage is 220 and at the output 185 V, so less. We see this part of the white color which is made of ceramic, the ceramic is 100% insulator but also excellent heat tolerance, inside this part are two holes filled with thin round graphite sheets. Graphite is an excellent conductor, but due to the large amount of these leaves that lightly touch, there is resistance to the movement of current, which is indicated by a red line and blue arrows. On the upper side there is a metal bridge under which there is a copper sheet that simultaneously compresses both "pillars" of graphite sheets, the compression itself weakens the resistance (increases
output voltage). 

In the middle of this ceramic element there is a metal "stick" which has a nut at its other end (a dashed black line with a transverse red line) (5), when the foot is pressed on the pedal the voltage already passes, when a situation is created that the resistance is over 0 (zero) then this nut connects the two contact plates on the other side and thus the flow of voltage through the pedal is practically without resistance and the sewing machine motor rotates at full power and speed.This nut is adjustable from the bottom and this is also done with OM meter , it is desirable to work

pedals and was "elastic", ie, that there are no sudden transitions of the speed of the electric motor. I hope this is clear ☺.
At "full throttle", the current seeks the shortest path, and then the graphite sheets are not under any voltage load. Well, we built that ceramic part (6), the wires should be inspected so that they are not in any case in poor contact or interruption, the capacitor is there to "absorb" the spark that occurs inside the ceramic part, nowadays it is not useful, it served sometimes not to interfere with the work of TV and
radio, today that technique has gone quite far and that capacitor no longer has any special role but let it, it doesn't matter.
Now we will disassemble and remove everything from and from the ceramic part (Fig. 7). In the attached picture we see graphite sheets, there is no need to touch them, it is desirable to clean the contacts marked with a blue arrow. The ceramic part itself can be well dusted with compressed air, everything must be dry, do not lubricate anything. First, the lower screws are inserted, for which the contact plates are tightened, they have
its place and you should pay attention to it, then put the leaves back, carefully, they must be nicely arranged, they must not be placed transversely, stuck, etc., their number in both columns is not important, it is important that they are approximately at the same level when return to the ceramic part. Then we put the final, slightly stronger graphite-ceramic parts on the upper side and then the metal bridge, then there is a central screw on which the spring is previously placed and the contact ones are tightened on the lower side.
sheets, thermal insulation pads are placed under them. Do not overtighten unnecessarily, align them and use the opportunity and adjust the central contact nut nicely with the OM meter, it moves a little harder and needs it for its stability.
We put the complete part back, tighten it with screws and a piece of thermal insulation material is placed under the ceramic part. If you have removed the springs, put them back, carefully, these are slightly stronger springs (10). Now we put everything under voltage again, CAUTION, the bottom cover is not placed in the picture, you MUST put it before plugging in.
Let's go "gas", the engine is started, a small foil curtain is started by the engine fan (11).
Thus, this work was completed with the fact that this was a completely correct pedal, the fault was in the motor, the wire was placed incorrectly 😀

1 comment:

  1. Anonymous21.9.16

    I'm a Bernina fan.This is excellent,thank you very much.