The watch reached me in a pitiable condition. Nothing worked anymore. Neither the hands let move, nor did the balance wheel swing.
The Junghans J90 has a size of 11.5''' and is the only movement with a cylinder escapement with the smaller Junghans J91 (8 3/4'''). It exists in two versions, with 1 Jewel and with six. The present watch has only one jewel. The hands and dial could be easily removed and at the first glance under the dial was a very dirty and rust attacked movement visible.
The wheels of the normally reliable functioning rocking bar were completely locked together.
The set lever and its screw were a single lump of rust. Also the dial side bearing of the balance shaft showed on the back signs of significant rust.
The angle lever and the rocker were first thoroughly bathed in rust remover.
The following dismantling showed more and more damage. The cylinder axis of the balance was also heavily eaten by the rust and no longer usable.
The escape wheel initially seemed fine.
Under the rocking bar, the three wheels were very dirty and the actual condition could only be assessed after a cleaning. Neither the winding nor setting mechanism worked.
The set lever had become an inseparable unit of rust with its screw. The screw crumbled and the angle lever broke while trying to fix it with the tweezers.
The search in the fund for a suitable angle lever and its screw proved to be hopeless.
Unfortunately, the escape wheel, which initially appeared intact when installed, had also become a victim of rust. A tooth crumbled only by placing it on the surface.
The disassembly of the gear train was routine and no major damage occurred here.
To tie the rust a little, I sprayed the entire movement with WD 40. At the places where the gilding peeled off, the movements' plates also showed damage.
While the pre-cleaned parts in the cleaning machine are rotating, the dial has been carefully freed from superficial dirt. The hands also got a little attention.
Fresh from the cleaning machine, the spare parts were crawled through. A new Plexiglas was needed, an set lever with screw, a new escapement wheel and a balance shaft...
In the old furnishing box were some parts to find, an escape wheel, a complete balance with spiral, but unfortunately no set lever.
After a few days the remontage could be started. Fortunately, a good friend and Junghans collector could still find a set lever with screw (thanks again Jens !!!).
The new (also old and used) balance with spiral was exchanged.
During the cleaning of the new balance, the gilding of the balance wheel unfortunately almost completely disappeared.
The dial side was largely reassembled without replacement parts. Although the three wheels of the rocker bar showed slight rust, the function was not impaired in the first tests. The parts were used again.
Only a new second hand was missing, but finally there was a matching one.
The watch has devoured a lot of spare parts and the gear is still irregular, but over the day it is still "only" about four minutes in the minus.
For trial purposes, a simple strap on is used, which would permanently damage the bottom of the watch and leave its mark.
Finally, the revision of this watch was a lot of fun and I was able to make some experiences and learn new things.