The Camera Craftsman Magazine was a specialist magazine for camera technicians and service professionals that appeared periodically until 1980 and was published in the USA.
An invaluable source of practical tips and repair instructions as well as background information, accessible on Learn Camera Repair:
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The July/August 1978 issue began a multi-part series on basic photographic circuits in cameras:
Larry Lyells, the author, was the magazine's technical director. We owe him countless technical articles, including in other specialist journals for photo technology.
I don't know of anything comparable, except the
The SPT Journal & Service Notes, highly recommended for anyone who likes „to look under the prism“.
It is also very interesting to follow the massive emergence of electronics in camera technology in the articles, which practitioners had to cope with in the 1970s. This meant spending on training and investing in equipment and tools for service.
Something similar happened again with the rapid triumph of digital photography at the beginning of the new millennium.