Pentax MX Meter Fix

by Todd on July 24, 2011

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.

Here is photo of the bottom of the camera with the baseplate removed. The red box indicates the region that’s been enlarged for the fourth and final image, appearing just below it:

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.

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{ 18 comments… read them below or add one }

Sluggo July 25, 2011 at 2:01 am

Nice complete write-up and clear photos. I did the same repair a couple of years ago on my currently used MX, and another MX is coming in the mail that supposedly just has meter problems, so I might get lucky again.

Your essay here is well done and should help more people keep these excellent cameras in service.

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lorenz July 26, 2011 at 5:47 am

thx you, i just wondered why the batteries are used up that quickly. i just fiddled around with the contacts pressing them gently apart and it works like a charm now. the threshold when between constant off and constant on is very small, but its manageable. also the base plate is very easy to put off and on again, no threat of things falling apart an ruining it all.

cheers and thx!

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Philip Greene August 16, 2011 at 6:20 pm

Thanks for posting this. A neighbor gave me a Pentax MX with a meter that wont shut off draining the batteries fairly quickly. I had the same thought a few weeks after researching the problem – that no one really explained what was supposed to be touching what and when – only referrals to the problem area and that something was supposed to be bent?I’ll have another look at my camera now and see if I can figure it out finally. I just don’t want to bend in the wrong direction and break anything so I am trying to be clear on what I need to do before I try it.

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Todd August 16, 2011 at 6:24 pm

Thanks for reading and commenting, I’m glad this could actually help someone. Good luck with it Philip!

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Joel October 13, 2011 at 12:09 pm

This is exactly the fix i am looking for on my mx camera which doesn’t give me the meter reading. I will be trying this fix today. tnx a lot. Wish me luck !!

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prima March 20, 2012 at 9:54 pm

thanks Todd for your information…i use pentax mx too (black body)…i’m from indonesia…

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Todd March 22, 2012 at 8:24 am

Thanks for the comments, everyone, I really do hope this helped some people. My MX eventually went back to having the same problem. Presumably I just didn’t bend the part enough, and I can redo the fix, but I haven’t had the time, and wasn’t highly motivated because the MX began to show other issues (film spacing, for example). I do like using old gear, and the MX is a solid, beautiful piece of equipment. But lately I’ve been picking up the F100 more often than anything else, just for convenience and dependability. This leads me to want something similar in nature that allows me to attach Pentax lenses, so I’ve ordered a PZ-1. Still eyeing an MZ-S as well. :)

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Fraser Morrison October 23, 2012 at 11:52 am

Thanks for this.I also saw other posts giving advice to adjust the contacts but none with the detail you supplied.Everything working again…for now !!,that said, if I have to take the base plate off again I think the screws will have had it.

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Todd October 26, 2012 at 6:28 pm

Heh…for me the biggest issue with the screws was not losing them! Glad this helped, and I hope the fix lasts.

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Spencer October 26, 2012 at 5:09 pm

Thanks for the info. Does taking the base plate off expose the film if you’re half way through a roll? Should I wait until I’m done the roll to try the repair? Thanks

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Todd October 26, 2012 at 6:29 pm

Great question, Spencer. Honestly, I have no idea. But I think we both know the safe answer. ;)

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Spencer October 26, 2012 at 6:49 pm

Ya, well put. I’ll wait. Thanks for the quick reply.

bob santos October 29, 2012 at 9:31 pm

Hi Todd, very nice write-up with detailed pics. I found this when trying to find a solution to fix my mx with a jammed/stucked rewind lever. No luck so far.

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Todd November 18, 2012 at 2:04 pm

Thanks, Bob. I have no idea on that one. Hope you’ve had some luck since posting this!

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Antipattern December 7, 2012 at 7:58 pm

I have just acquired a ME Super that didn’t show any meter readings, and there is a similar mechanism, it seems, just at a different place. (the ME Super looks very different, as you say) I pressed the shutter to figure out which lever did what, fiddled around with it, and now the ME-S gives me meter readings again. Cheers for that!

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Todd December 7, 2012 at 7:59 pm

Great news, thanks for posting. :)

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Steve March 25, 2014 at 11:53 am

Almost 3 years later, this guide is still helping people out. I just bought a MX with constant-on meter, with this page it was a 5 minute fix. Thanks!

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Todd March 25, 2014 at 12:09 pm

Steve, thanks for checking in. I think this post accounts for about 80% of the traffic to my blog. :P

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