Mamiya M645 repair & common faults
Excellent coverageThe Mamiya M645 is a mid-1970s medium format SLR built around interchangeable film backs, viewfinders and prisms, aimed at professionals wanting 645 negatives without a full studio system. It has no meter of its own; metering only exists if a metering prism is fitted. The shutter release is electronic even though the shutter itself is a cloth focal-plane unit, so a battery is needed for the camera to fire at all.
Interchangeable finders and prisms · CdS metering in the accessory prism only · Electronically released cloth focal-plane shutter · 4LR44 (6V) battery · Interchangeable 120/220 film backs
Common Mamiya M645 faults
Mamiya M645 shutter won't fire
This is usually the body's own safety interlocks doing their job rather than a fault. Release is blocked unless the film back is fully seated, the dark slide is out, and the shutter is wound on. Because the release itself is electronic, a flat or missing battery gives the exact same dead response. Check the battery before assuming anything mechanical has failed.
Mamiya M645 light meter not working
The M645 only meters through its accessory metering prism, so a body fitted with a plain finder will never show a reading, that's normal and not a fault. On a metering prism, a dead or sluggish needle usually points to the CdS cell or its wiring ageing, or corroded contacts. Fresh cells are worth trying first, since a flat battery mimics a genuine meter failure.
Mamiya M645 mirror stuck up
A mirror that stays up after firing points to the return mechanism binding, often old foam or grease around the linkage stiffening with age. It's common on bodies that have sat unused for a long stretch. Winding the film advance on sometimes frees it, which is worth trying before concluding the mirror mechanism itself needs proper attention.
Mamiya M645 film back light leaks
Fogged edges or diagonal streaks on frames point to the foam seals inside the interchangeable back perishing with age, letting light reach the film at the joins. It's an extremely common fault on backs of this age regardless of how the body itself performs. Check that the dark slide seats and locks positively, since a loose or worn slide can cause a similar leak.
Mamiya M645 wind crank stuck
If the crank turns but won't complete a stroke, or feels rough partway through, it usually points to wear or binding in the advance train, which cocks the mirror and shutter together on this body. A jammed dark slide or a back that isn't seated properly can produce the same stall, so confirm the back is locked on and the slide fully withdrawn first.
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Try it now ›Scatto is a reference tool for people who service film cameras. It explains mechanisms and quotes service data, but it cannot see your camera at the bench, so verify anything load-bearing before you act on it.