I recently acquired a Pentax MX in reasonable condition. I’ve been in search of this camera for some time. I have others of this series but all require a battery to operate unlike the MX which only needs a battery for the light meter. I was pleased to find that most of the shutter speeds worked, however the light meter did not, which is not uncommon for this camera.
On getting the camera home, the battery compartment was clean but the cap had some corrosion on it. I have found a cleaning bud and surgical spirit to do a good job of cleaning it up.
On putting a fresh set of batteries in the camera sadly the meter still did not work. A little research pointed to a possible simple solution. The battery cap has a plastic insert that keeps the batteries in place.
On removing this and refitting the batteries the meter worked. Success!
Having left the batteries in the camera overnight, I was dismayed to find the following morning, that the meter no longer worked. Back to square one! A little more digging around the internet revealed a further reason why the meter may not be working.
This time I would have to take the base plate off.
The light meter circuit consists of two pieces of metal coming in contact with each other to form a circuit. These are normally kept apart except when the shutter button is pressed half way down, which brings the two metal contacts together.
The picture above shows the metal contacts looking down on them. If we were able to look at them from the side we would see something like the drawing below.
Over time, the metal gets bent so that it is always in contact and thus drains the battery. This was the problem I had , the two pieces of metal were in contact all the time.
I simply placed a small screwdriver between the two pieces of metal and adjusted them so that the pieces of metal no longer touched.
Sure enough when putting it all back together the meter was again working. Job done!
It is very gratifying when there is a simple solution that ends in a fully working camera.