Mamiya 7: No Finder LED Display After Impact Damage
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Interesting repair on a Mamiya 7: the camera was impact damaged and the obvious sign was the damaged battery compartment. The complaint was that the LED meter display would not illuminate in the finder, but the shutter did work. After disassembly, I found that the damaged battery box had pushed up to the interior of the plastic grip and was causing a slight leakage to ground. This was enough so that the battery could put out enough current to fire the shutter but not the LED display. After fixing up the battery box and repositioning the circuit board which had also been pushed up to the grip, all is well. Of course, the rangefinder was also off by quite a bit so that got taken care of.
For those that might enjoy some of the nitty gritty details of this repair, I have posted some photos and will explain them:
Photo four shows the grip and you can see that although it is plastic, it is conductive (47 ohms)! This is because the interior of the grip is coated with a conductive material. Canon was probably the first to do this with the plastic top cover in 1978 on the A-1.
Photo five shows current draw in standby after the repair. The 4 micro amps is within specs. Almost all cameras and electronic devices these days draw current (micro amps) when “turned off”. When this camera came into the shop, the battery read 5.15 volts with no load and under load probably close the minimum voltage needed of 4.3 volts.
The final photo shows the silver frame finder reflector indicating that this is an early model. In fact, it is one of the earliest I can recall seeing as it was produced in April 1995.
