There is a story going around through various web sites that there is a simple fix for a IIIa light meter that doesn't work. According to these experts the problem is oxidation of the electrical contacts to the photocell and that all one needs to do is to remove the cell, take a blade and scrape the contacts. This is supposed to restore the meter to normal operation.
The fact is that about one of every five IIIa camera I receive for servicing has damage to the cell contacts caused by scraping. Zeiss understood corrosion, and in most of their light meters the cell contacts were gold plated to eliminate the possibility of corrosion and to ensure long term good electrical contact. In its last production meters Zeiss dispensed with mechanical cell contacts completely and changed to using permanent soldered connections. There is no need to scrape the contacts. Corrosion is the problem, but it is corrosion to the cell itself, and not to the electrical contacts. The following illustration of the ideal selenium photocell shows what I mean by this.
The cells in Contax IIIa cameras are all old. While some may respond to light, the meter cannot possibly be accurate or linear with an old cell in it. The only way to restore the meter to like new operation is to have a new cell installed in it. There is absolutely no substitute for this. When I replace a cell I use the Zeiss method to solder it in place to completely eliminate the friction type contact source of unreliability.
There are almost no workers who work on the Contax IIIa light meter. I am happy to work on them and am expert in restoring meters to full operation, even those which have been written off by other experts.
If your IIIa meter has a problem and you want it made right correctly please write to me.