Gossen-Bolex Light Meter Repair

I have had a Gossen light meter for Bolex for a while, but the one I have is missing the trim screw and the protective clear plastic over the dial.
It is also the older model with a smaller lens on the front. Also, it was missing the incident light diffuser.

I recently found a newer version, however, its readings were pretty far off.

So, time to open it and check it out...

Newer meter on the LEFT and older meter on the RIGHT.

Removing the chrome trim screw in the middle of the dial allows access the the screw which holds everything in place. The whole dial needs to come off by rotating it about 90 degrees. Then it should be free to come apart.

Under the dial are two long screws that hold the case together.

With the case open, one then has access to the trimmer potentiometer. It is wrapped in tape and stuffed under the meter face. Mine was also held in place with rubber cement. They made it so there is enough slack on the yellow wires to safely pull the potentiometer out for adjustment.

Last year I made this calibrated light source, and it really gets a lot of use.
The manual does not indicate the K value for the meter but I calibrated it to K=14.03 with a zinc cell.

After calibration I re-assembled it. I'll keep the older one as a working spare.