A few weeks ago the meter in my Pentax MX stopped working. I assumed it was simply dead batteries, and bought some new ones. Only yesterday I put in fresh batteries, because I wanted to use the camera. But the meter was still not working. No lights at all. This camera is 35-ish years old, and it’s never been worked on, to my knowledge (I purchased it on eBay from the original owner, who said it had never had any maintenance). So despite being in reasonable condition for its age, it’s still old, and not exactly clean. I plan to send it to Eric one day soon for some general cleaning and evaluation, but I haven’t had the time. But I decided to do a bit of Googling to see if I could find an easy repair to get me through for a while. I easily found some threads about the issue on Flickr and Pentax Forums, among other places, and it became clear that there were some bendable contacts inside which could be the cause of the problem. It’s not uncommon for these contacts to become bent in such as way as to either make the meter stay on indefinitely, or to prevent it from coming on at all. I even found a few photos, but no detailed explanation of precisely when and where the connections were made.
Still, I decided to remove the camera’s baseplate and look around in hopes of figuring it out. After a fair bit of fiddling (I’m not necessarily mechanically inclined), I managed to see how the setup was supposed to function. I made an experimental adjustment to one of the contacts, reinstalled the baseplate, and sure enough, it’s fixed! I could have done this in a lot less time if I had had a clear explanation of how to do it, so I decided to take a few snapshots and provide a quickie tutorial. I hope it helps someone in the future.
The first photo shows the baseplate still on the camera, and the red arrows indicate the screws which need to be removed to pull off the plate. As you might note, one of the screws doesn’t have any black paint on it, so perhaps someone has been inside the camera before, or maybe it just wore off. This repair is not difficult, but the most sensitive part is probably the removal of the screws. They are tiny, and easily stripped. Fortunately for me, none of them were seized with age, and I was able to remove them (you’ll need a very small screwdriver) without any damage. The second image shows the screws sitting on a penny for size comparison.
This last image shows the copper contacts and the mechanism of actuation of the meter. There’s some kind of insulating material (A) sandwiched between the lower (B) and upper (C) contacts. Note that ‘upper’ and ‘lower’ here refer to what their relative positions would be when the camera is in normal shooting orientation. Contact (B) has an L-bend in it, and the arrow leading from (E) points to the apex of the right angle bend. I’m hoping this is clear! It’s about the best I could do quickly with a two-dimensional photograph, and I don’t feel like making a rotated diagram tonight.;)
In this image, the repair–a simple bend of contact (C)–has already been done, and the camera is just sitting without the shutter button being depressed. You should be able to see that contacts (B) and (C) are not touching. When the end of the short section of the ‘L’ of (B) touches (C), the circuit is completed, and the meter activates. In the normal state shown here, contact (C) is held up (toward the top of the camera) by that yellow insulated protrusion, which is attached to a post that’s pushed downward by the shutter button. When the shutter button is pressed halfway, the yellow piece is pushed toward the bottom of the camera (toward us, in the picture), and it only has to move a millimeter or so to allow (C) to come into contact with (B), thus activating the meter. Pretty simple.
In my case, contact (C) somehow got bent upward toward the top of the camera, so it was never even resting against the yellow piece, and wouldn’t close the connection, even when the shutter button was pressed all the way down. To move it, I just held the camera in one hand, simultaneously holding the shutter button down for easier access, and with a small screwdriver, I bent contact (C) up toward me (toward the bottom of the camera) just a tiny bit. Got it on the first try, and it seems to be working just fine now. I am assuming that in cases where the meter becomes constitutively active, contact (B) gets somehow bent up toward the top of the camera and maybe slightly toward the right side (left in the photo), so that it’s always touching contact (C).
Well, that was a lot longer than I planned on it being, but I wanted to make sure everything was clear. Hopefully I’ve succeeded. FWIW, I also took the bottom plate off of my Pentax ME Super, thinking maybe the mechanism would be the same (this was before I grasped how it worked), but it’s not. I have no idea how this mechanism varies among other cameras of this approximate age.