Mamiya 7 65mm Lens: Testing for a Broken Flex Cable
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This post is another one about the Mamiya 7 65mm lens. I see a lot of these lenses in the shop with the issue of a broken flex cable. If you are purchasing one of these lenses, check it carefully. The symptom is that the red light meter warning at the bottom right of the display will flash and the meter will not work.
In the video, I show how I quickly check these lenses for a broken flex cable. The lens fixture outputs to a VOM and at the beginning of the video, I am changing from minimum aperture to largest aperture on the lens and you can see the resistance via the meter needle changing from high to low and back again. So far this looks like all is working. But in the later half of the video I turn the focus ring and you can see that the resistance goes to full open and this will cause the meter to not receive aperture info and not work.
To replace the flex, the lens needs a fairly good disassembly as shown in photo two. Photo three shows the flex cable out of the lens and ready to get de-soldered from the lens contact assembly. You need to be careful at this point as too much heat on the pins from a soldering pencil will cause the plastic of the contact base to melt.
What was interesting about this particular example was that it had previously been repaired for this same problem. But, a jumper wire was added instead of replacing the cable and this is visible in photo four. Actually, the repair was not done badly and held up alright except that the adjacent trace also developed a tear probably at a later date and that was causing the issue today. Photo five shows a close up of both broken traces.
A caution for working on these lenses without the proper equipment: Even to access the contacts for a patchwork repair, the rangefinder unit needs to be taken out and if you don’t have the tools to properly calibrate it, the lens will not be within specs. In the case of this lens, the rangefinder was out by -0.10mm. That’s way too much. Farthest out spec should be -0.015.
