La Cimbali Junior D/1 rebuilding dosing control knob

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by mclearn »

Hi all. Long-time lurker, first time poster.

I have a La Cimbali Junior D/1, circa 1993 or so that I have been hard at work rebuilding. Dating it is hard to tell because there are no obvious dates on the labels under the drip tray. (The heater element brass fitting has a date stamp of 1993 which is the only definitive thing I can go on. This is the D/1 model with the 4 coffee doses selectable via a knob on the front panel.

I recently had everything removed and carefully cleaned. The frame was sandblasted and powder coated and it looks great. Excited to put it together and I was putting all of the the electrics back together this weekend. After attaching the knobs to the front, I experimented to make sure they worked well and unfortunately the "dose selector" knob was extremely sticky.

For reference, the knob is pictured below connected into the system.

So I did what any reasonable person might do who just spent a long time ripping apart every other system, and I opened that too. Unfortunately, it was booby-trapped with springs and small brass pieces. I managed to rebuild all of the bits, and I tried to infer the correct orientation of the internals, but I cannot determine if I got it all back together again. I wanted to use the wiring diagram to help determine if I had it correct. Here's the wiring diagram from another post on HB:

Does anyone know how to test the knob selector to make sure it is selecting properly relative to the printed dosing on the front cover? The wiring diagram suggests that R has a significant role to play. However, continuity testing with R and the dosing rods in the chamber gives me strange results.

I realize I could always get the machine put together, pull some shots and determine what I've done and fix if necessary. However, if anyone has some ideas at this early stage to let me confirm appropriate settings, I'd appreciate it.

In case anyone is interested, here are the details of the inside of this knob:

Inside of each of the chambers are two very carefully oriented notched discs. The two chambers are exactly the same on the inside and the only difference is how the notched discs are oriented.

The notched discs permit the brass contacts (with the help of a spring) to either make or break contact depending on the position of the notch. The two bolts which go through the entire length of the unit help to align everything. I've marked the location of the spring-loaded brass contact plates on both chambers (well, at least where they would go on the other one after the rebuild).

The square metal axel runs the length of the center of the notched discs and attach to the knob. Turning the knob causes the notched discs to turn and permits the contacts in each of the two chambers to open and close. The knob component on the far right of the picture with the old yellowing grease is another spring-loaded mechanism (those springs are at least 10x stronger than the others!) and as far as I can tell provide the resistance and tactile feedback to the knob operator to know it is in one of the four positions without it slipping.


#2: Post by quadra »

hey Mclearn, did you manage to get this sorted? if not let me know and I will walk you through it! I wonder if you would be willing to share some better pictures of your selector panel ? those graphics are usually pretty beaten up and it would be nice to try to redo mine from a good image.