Forget about loading the camera with
negative film.
Get a roll of slide film. Load that into the camera, paying attention to set the correct ISO on the dial (this is fiddly if you don't have perfect eyesight).
Shoot in both bright daylight and overcast ("diffuse") light. Take written notes of the aperture and shutter speed you have used across the roll.
A waning or drifting TTL meter will show glaring errors in exposure because slide film does not have the overly generous latitude for under- or over-exposure that is such an endearing feature of negative film.
If meter errors are plainly visible and persistent, the camera requires service. This is especially so of the now very old Pentax 6x7 cameras (as opposed to the moderately old, later generation Pentax 67 bodies [1989 onwards] ).
Other errors are poor correlation of shutter speeds (marked shutter speeds are typically slower when firing), irregular frame spacing (large and larger gaps or overlap of frames), inaccurate shutter travel (some frames partially exposed, others not), battery compartment corrosion and the condition (or even absence!) of the meter coupling chain.
Foam seals on the base of TTL or non-ttl meter prisms wear down over time. This can mean the prism can 'wobble' slightly, and in certain circumstances, come away from the camera completely if tilted to portrait (vertical) orientation. Replacement seals are available, but the task is a grubby and tedious affair.
About the meter coupling chain. This is the 6x7's achilles heel and requires an awareness that incorrect prism-lens procedure can give rise to breakage. It is a bummer that requires disassembly of the camera's front (e.g. the attention of Eric H., mentioned in the foregoing post). This brings us to the first rule:
If you remove the prism, then remove the lens.
Re-mount the prism, and then re-mount the lens.
This resets the chain and meter coupling.
Above all else,
use the camera frequently and when not in use, keep the shutter speed dial on either B or X, not on a marked shutter speed.
Last edited by Silent Street; 01-08-2017 at 04:32 PM.