Repair of the Chinaglia Multimeter "CORTINA ELECTRO"Lorenzo De Luca ·
In this article we will discuss the repair of the multimeter (or as it was called in the manual “analyzer”) Chinaglia Mod. "Cortina Electro," manufactured in the 1970s in Belluno and kindly donated to the laboratory by a local collector and electronics expert.
Although such an instrument is now outdated by more high-performance modern instruments, for me it remains a piece of measurement instrumentation history, with the added bonus that it was made by a local firm, at the time famous in Italy and abroad.
Moreover, this instrument has even greater value to me because my grandfather also owned a Chinaglia multimeter, which I now own, and which has an important place in my multimeter collection.
Repair of the current and voltage measuring circuit
The multimeter is found already opened, perhaps from a previous repair attempt, and is not functional. immediately you notice some resistors completely burned down to char.
It is therefore decided to replace them, but given the state they are in it is not possible to measure them because they are now a completely open circuit, so the paper manual of the multimeter that was given to me along with the instrument and whose scan is now attached to this article comes to the rescue.
However, the values required are special and not found in the classic standard resistors nor available for purchase, so it is decided to make custom resistors by using standard resistors and adding series and parallels, measuring with a 4-wire fixture the resistance obtained until the exact value is achieved.
Repair of the resistance measuring circuit
The resistance measurement function is still not working perfectly, and this is the only measurement that requires the use of two AA batteries in series installed in the instrument.
I notice, however, that although there is no significant current demand from the instrument and the fuse is intact, after the fuse holder I read a voltage of only 0.6V, much less than the 3.2 I measure before the fuse holder itself.
The problem is identified as corrosion of the fuse holder contacts, so it is decided, while waiting to install a non-corroded fuse holder, to solder the fuse onto the fuse holder contacts properly cleaned of oxide.
After this modification and verifying that the battery voltage now reaches the analyzer circuit, the ohmmeter also begins to work properly.
Also today we come to the successful conclusion of the repair, the instrument is back in working order and after a calibration and external cleaning it can really be said to be as if it just came off the production line.
If you have not already seen it, it is also worth reading the blog article on the repair of the Keithley 130 multimeter, which most likely contributed along with the digital multimeters of that period to make the beautiful Chinaglia obsolete.