This is the schematic diagram for a Z80 plug-in module for the //c. 

I don't know the manufacturer. The pcb has a yellow color and the name 
'Cirtech' is written on it. Cirtech seems to be a pcb etching company 
in Switzerland. There is also a US patent code written on it, the patent 
claims an etching process for double-sided pcbs.

The markings on the ICs have been removed, therefore I had to guess the 
part numbers. All TTL parts were obvious, but I don't have any information
whether they are LS, S or HCTs.


Patrick