Pentax 645N repair & common faults
Excellent coverageThe 645N is Pentax's second-generation 645 body, launched in 1997 and the first in the line with autofocus. It pairs a TTL autofocus and metering system with an electronically controlled vertical metal shutter, so almost everything the camera does depends on the health of its electronics and its 6V lithium cell rather than pure mechanics.
TTL autofocus SLR · electronically controlled vertical metal shutter · program/aperture/shutter-priority AE · 6 V 2CR5 lithium · Pentax 645 mount
Common Pentax 645N faults
Pentax 645N LCD screen has missing or faded segments
The top control panel uses a liquid crystal display to show shutter speed, aperture and frame count. On bodies of this age the display fluid or its seal commonly degrades, so patches fade, blacken or disappear. It is a display fault rather than a sign the electronics underneath have failed, and the camera will often still meter, focus and fire normally despite what the panel shows.
Pentax 645N shutter won't fire
Release on this body is electronic throughout, the mirror and shutter cycle only runs with power behind it. A dead or corroded 2CR5 cell is the most common cause, followed by a mirror or shutter mechanism stuck partway through its cycle. Try a fresh battery first. If the mirror is visibly up or the finder stays dark, that points to a mechanical stall rather than power.
Pentax 645N autofocus won't lock or keeps hunting
The 645N reads focus through the lens and drives the lens motor via a coupling in the mount. Hunting or a refusal to lock can come from a worn or dirty coupling, a tired AF sensor, or simply low light and low subject contrast, which this generation of AF struggles with. Try the lens in good light on a contrasty subject before assuming a fault.
Pentax 645N exposure is consistently wrong
Metering runs off a cell behind the mirror feeding the program, aperture-priority and shutter-priority modes. Consistent over or under exposure usually traces to a meter that has drifted with age, exposure compensation left dialled away from zero, or a shutter no longer holding its marked speeds. Check the compensation dial reads zero before assuming the metering circuit itself is at fault.
Pentax 645N mirror is noisy or hangs before dropping
The mirror box uses a foam damper to cushion the mirror at the top of its swing, and on cameras this age the foam commonly turns sticky as it breaks down. That shows up as extra mirror slap, a mirror that hesitates before returning, or a gritty feel through the finder. It is a wear-part issue rather than a sign of a deeper mechanical fault.
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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.