I bought my first Pentax SLR, an S1a, and a clip-on light meter in 1968. The camera had one CLA in the late eighties, but at the time that the camera and meter were destroyed in a fire in 2008 not a screw had been touched on the meter, but it was still working perfectly. My wife and I used the camera, with and without the meter, for most of those forty years, so for nostalgic reasons in 2009 I replaced the S1a with an H1a from a local film camera dealer. In early 2011 I purchased a meter in fine external condition, and advertised as working, from an online shop, but when it arrived I was disappointed to find that the needle was stuck. I searched online for instructions on disassembling and repairing Pentax clip-on meters, but I never found anything that tells as much as how to get the cover off. So with a bit of experience in camera repair, and some knowledge of the delicacy of galvanometers--having destroyed a couple when I was a kid--I decided to open my light meter and see if I could fix it. Being successful, I decided to make my notes available to anyone who would like to attempt the same thing.
These instructions apply to the type 2 clip-on light meter, the square-cornered one. I have never even held an earlier type 1 meter, the round one, so I have no idea whether any of this information applies to it. From the photographs of it I've seen, I suspect not.
The user guide for the meter is in the Pentax online archives at http://c758710.r10.cf2.rackcdn.com/files/support/manual/184_1314744935-53897465_manual.pdf. I hope to include some clearer photographs here someday, but for now the illustrations in the Pentax guide will have to do. All letters in parentheses in the instructions below refer to the illustration "Major Parts of the Honeywell Pentax Clip-on Exposure Meter" in the user guide. I've tried to use the same names for parts as well, except for "film speed setting dial," which seems clearer to me than "film speed setting," which the guide uses for the part labeled (A).
1. Remove the meter from the camera and put the L-Off-H switch (D) in the middle position, Off. (The Pentax guide calls this the "Lo," "Hi," and "Off" switch.)
2. There are two set screws in the bottom of the film speed setting dial (A) and two set screws in the side, one under the letters “ASA” and one under “1600.” First, loosen the set screws in the bottom of the film speed setting dial until they project about 2–3 mm. It isn’t necessary to take them out, but if you do, the tiny springs under them and the tiny ball bearings under the springs may fall out through the holes. If you don’t remove the screws, springs, and ball bearings through the screw holes, be careful not to lose the bearings and/or the springs when you remove the film speed setting dial.
3. Loosen the set screws in the side of the film speed setting dial (A) so that the dial can be separated from the film speed dial (B, with the index dot on it) and the shutter speed dial (C) on top. Lift the shutter speed dial and slide its shaft out of the meter.
4. Unscrew the screw under the shutter speed dial (C) and the screw on the opposite side of the body of the meter. Unscrew the light window mount (H) at the front of the meter. Use a rubber gasket or rubber-padded pliers to grip the outside edge of the mount without damaging it. The top will then lift off the meter.
5. Watch out for any screws or parts that might have come loose inside the meter. In my meter, the little brass screw and spring plate that hold the galvanometer in place had come loose, and the spring plate had fallen inside the galvanometer, preventing it from rotating.
6. To recalibrate the needle I used a 1.4-volt 675 zinc-air hearing aid battery. Insert a fresh battery and then press the green battery check button (E) at the top of the pivot shaft of the L-Off-H switch. If the galvanometer is working, the needle should move toward the small green patch at the bottom of the meter dial. If the needle stops before or after the green patch, adjust it by turning the zero adjust screw (N) on the bottom of the meter next to the battery. Careful: turn the zero adjust screw only a few degrees at a time; a small angle of adjustment can make a large change in the needle’s position.
7. When I took the top off my meter, the spring-loaded tape with the f-stop scale (G) printed on it came off the takeup reel geared to the film speed dial (B). If that happens, remove the two screws on each side of the meter and lift off the plate with the zebra stripes. Manually turn the spring-loaded tape reel clockwise (as seen from the rear of the meter) a few turns until spring tension is built up in it again and then reattach the tape to the geared reel with a bit of transparent adhesive tape. Try not to turn the geared reel, and try to attach the end of the tape at the same point on the reel that it was before.
8. Put the meter back together in the reverse order. After you get the cover and the L-Off-H dial back on, insert the shaft of the shutter speed dial (C), then attach the film speed setting dial (A) on the bottom of the shaft and hold it firmly against the film speed index dial (B) so that you can recalibrate the meter before tightening the set screws. If you took the springs and ball bearings out of the film speed setting dial, reinsert them, bearings first, in the bottom of the dial. That will be easier than trying to get the ball bearings to stay in position on the ends of the springs while you try to reassemble the dial. Turn the bottom set screws until they are flush with the bottom of the dial.
9. To recalibrate the Pentax meter, use a reliable comparative light meter as your standard to establish the correct settings for a particular light source. Take a reading with the comparative meter at a set distance from your light source and find the f-stop for a particular speed and ASA (ISO). For example, my comparative meter set at ASA 200 showed f/4 at 1/60 second. (I used an old Kalimar meter that I know to be accurate. There's no reason you can't use a digital camera with manual adjustments or even an iPhone app, but it seemed more appropriate to me to use an analog meter of approximately the same vintage as the Pentax meter.)
10. If you’re using an indoor light source, as I did, you’ll want to set the Pentax meter’s L-Off-H switch to L. Then hold it at the same point where you held the comparative light meter and turn the film speed index dial (B) until the correct aperture shows opposite the needle’s position on the f-stop scale (G). Hold the film speed index dial (B, the one with the dot) steady and turn the film speed setting dial (A) until the speed you’re using shows opposite the film speed index mark (P).
11. Now comes the hard part. While keeping the f-stop scale (G) in the same position on the meter dial and holding your film speed setting on (A) and (B) with one hand, turn the shutter speed dial (C) with the other. Once you get all three dials to show the settings you established with the comparative meter, hold the dial parts together while you tighten the set screws in the side of the film speed setting dial (A).
12. After they are tightened, turn the set screws in the bottom of the film speed setting dial (A) until the dial turns firmly, but not too tightly, with a nice click into each setting.
13. Attach the meter to the camera and make sure that the shutter speed on the meter's dial matches the set shutter speed on the camera. If the tape with the f-stop scale hasn’t come loose, the shutter speed coupling pin (O) at the bottom of the film speed setting dial (A) should fit into the slot of the camera speed dial so that both speed markings match.
14. If you've had to reattach the f-stop tape to its reel, you’ll probably find, when you mount the meter on your camera, that the speed shown on the meter doesn’t match the speed on the camera. That is, the position of the tape relative to the shutter speed coupling pin (O) has shifted. You’ll need to take the meter apart again and reposition the tape, and you may have to experiment until you get it correct. It’s tedious work, but after the third or fourth time you’ll get faster at stripping off the top and the zebra plate and putting everything back together again. It’s well worth the time spent if you get the meter working properly again. You may also be able to adjust the position of the geared tape reel by loosening its set screw, but my tape attached almost exactly over the screw, so I left well enough alone and moved the tape instead.
Good luck!
N. R. Parsons
11/9/2011