Mamiya M645 Super repair & common faults
Excellent coverageThe M645 Super is Mamiya's mid-1980s revision of the 645 system, built around interchangeable film backs, viewfinders and focusing screens rather than a fixed body. Its shutter is mechanically built but electronically timed, so the body needs a working battery to fire at all, and metering, where fitted, lives entirely inside the AE prism finder rather than the body itself.
Interchangeable roll-film backs (120/220) · mechanically built, electronically timed focal-plane shutter · interchangeable prism and waist-level finders · CdS metering in the AE prism finder, not the body · battery-dependent shutter release
Common Mamiya M645 Super faults
Mamiya M645 Super won't fire
The shutter is electronically timed, so a flat or corroded battery stops it firing regardless of which back or finder is fitted, worth checking first. The body carries a mechanical interlock with the film back, refusing to release unless a back is properly seated with the dark slide withdrawn. If a fresh battery and a seated back still won't release, the fault has moved into the shutter or mirror mechanism.
Mamiya M645 Super meter reads wrong or dead in the AE prism
Metering lives entirely in the AE prism finder rather than the body, so a dead body battery won't touch it, but the finder has its own cell, battery and contacts. A fresh finder battery and clean contacts are worth checking first. Otherwise the CdS cell can drift or fade with age, showing a reading that's consistently off rather than dead, a finder-specific fault rather than a body one.
Mamiya M645 Super shutter capping or uneven exposure at high speeds
One edge of the frame coming out darker than the other, worse at faster speeds and less visible at slower ones, points to the two focal-plane curtains no longer travelling in sync. Ageing curtain tapes losing tension, dried lubrication on the moving parts, or drift in the electronic timing governor are the usual causes. It's a shutter mechanism fault rather than anything a battery or contact clean will fix.
Mamiya M645 Super film back light leaks
Unexplained fogging along frame edges, usually worse in bright light, points to the back rather than the body since backs seal separately with their own foam and dark slide channel. Decades-old seal foam turns to a sticky crumble or compresses flat and stops sealing, and a dark slide that doesn't seat fully home leaves a gap. Worth confirming the slide is pushed fully home before assuming the seals have failed.
Mamiya M645 Super mirror stuck up or slow to return
A mirror that stays up after firing, or drops back with a delay, usually points to old grease thickening on the mirror box pivots and linkage, or the foam bumper the mirror lands on turning sticky or disintegrating. Return speed that's consistent but slow suggests drying grease, while a mirror that never frees points to something obstructing the box. It's a mechanical fault rather than an electrical one.
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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.