Mamiya Prismat CP mirror occasionally sticks in the up position
Asked 12/1/2020
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2 answers
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I have a Mamiya Prismat CP (1964, likely) film SLR. The mirror sometimes sticks in the up position after firing. Pulling the advance lever usually resets it. I initially suspected old foam or sticky internal lubrication, but this camera doesn’t appear to have the common foam ring issue. Before opening it up further, what should I check for, and what can cause this kind of intermittent mirror jam?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
3
So turns out my guesses were completely wrong. I did end up opening the camera and putting some drops of oil in recommended places, which didn't end up solving the issue.
However, during this process I removed the battery for the built in light meter. The original 1.3V battery is not really available anymore but I found out that a standard 1.4V hearing aid battery works quite well. they're also quite cheap. This battery happens to be just slightly thicker though. What I found out was that the mechanism suddenly worked perfectly when the battery was removed. Moreover it stopped working again when I applied light pressure to the bottom of the battery compartment. The pressure must be blocking some mechanism behind it just enough to be unreliable.
The issue was finally solved by dremeling the plastic on the back of of the battery compartment to be a bit thinner. I also made sure not to screw on the battery cap too tight.
Not sure if this is going to help anyone, but there it is. I know some others use the same batteries for old cameras, so it must happen more often.
Originally by user96199. Source · Licensed CC BY-SA 4.0
user96199
5y ago
0
Generated from our catalog & community — verify before relying on it.
In this case, the cause was not sticky foam or lubrication. The problem turned out to be interference from the light-meter battery/battery compartment.
The original meter battery was replaced with a hearing-aid cell that was slightly thicker than the intended battery. With the battery removed, the mirror mechanism worked normally. Applying light pressure to the bottom of the battery compartment made the fault return, suggesting the battery or battery-compartment fit was pressing on or obstructing part of the mechanism just enough to cause intermittent jamming.
So before assuming a full mechanical overhaul is needed, check:
- whether the battery is the correct size/type
- whether the battery compartment is deforming or pressing on internal parts
- whether the problem disappears with the battery removed
If the camera works reliably without the battery installed, the issue is likely physical interference rather than a mirror-box lubrication problem. Be cautious with adding oil—random lubrication can fail to fix the issue or make things worse. On older mechanical cameras, fit and clearance problems can sometimes mimic more serious internal faults.
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UniqueBot
AI5y ago