OM-40 (OM-PC): Battery Drain, Stuck Mirror, Top Cover Removal


My OM-40 drains the batteries too fast.
By far, the vast majority of "battery drain" complaints on the PC/40 are due to a sticky electromagnet -- trust me, they are. It's an easy fix -- pull of the front edge of the mask below the mirror and clean the surfaces between the magnet and armature _carefully_. Then replace the plate w/contact cement. In normal circumstances, good silver oxide batteries (use no substitutes!) _will_die_ in 6-12 months. If a dedicated flash is used, battery life will decline substantially. Lithium or alkaline batteries will die in a few weeks. Period, end of story.

My OM-40's shutter and/or mirror is stuck
The PC has 3 electromagnets -- one to control the exposure time, one to control the aperture arm in program mode, and one to release the first curtain. Any of them can get "sticky" -- sounds to me like the last one, the first curtain release magnet, is sticky.

The only long-term reliable solution is to have the camera disassembled and get this magnet assembly cleaned -- a full overhaul, of course. But you _might_ get it to break loose for a while by smacking the camera firmly against the palm of your hand. (Now, now, now -- it's a sturdy beast, a firm whack or two (or ten!) won't hurt it! Just don't leave a lens on it when you do!)

If this _does_ release the mirror, make a habit of _not_ winding the camera until just before you want to take a shot (off the top of my head, I don't recall for sure if leaving the camera un-wound keeps this magnet/armature separate, but it might). That is, until you've had the camera overhauled -- then don't bother, it's extremely rare to see this happen twice on the same camera.

I am trying to take an OM-40 apart. I unscrewed some screws but it seems that the ISO dial won't come off like it does in a OM-2 body.
  1. remove the rubber pad on top of the wind lever and the screw underneath -- everything else lifts off.
  2. Unscrew the screw from the center of the rewind knob (_never_ remove the screw from the knob of a 1/1n/2/2n) -- lift off the knob.
  3. Unscrew the plate underneath the rewind knob -- below it is the mode selector knob, and under it is a detent ball (2mm), holder, and spring (don't loose the holder!).
  4. _carefully_ pry off the plate over the ASA knob (slip the sharp point of an X-acto-type knife under the corner by the window and work it up -- work slowly and try not to crease it -- you can flatten it out later). Underneath is a small screw over a little plate, covering a conical spring (small turns to the top), that rests in a plastic cup that's keyed to the knob. Once this screw is removed, the knob will lift off.

Thereafter, you've got 6 screws that keep the top on. Underneath are three loose parts -- the spring that pushes down on the back latch, the rewind button that's keyed to the top cover, and the post that the rewind button rests on. And see -- there's no room to spare....

There's some wires attaching the top cover's circuit to the main circuit -- if you unsolder them, be sure to draw a precise diagram showing where the wires come from, as well as as many of the others that you can -- you never know when a wire will break off while you're working!

(BTW, the ASA knob of the OM-2/2n doesn't really "come off" -- it's bezel is staked onto the top cover, and most of the parts are attached from underneath. Yes, you can pull off a plate or two, but that's about it....)

contributed by Clint Rumbo