+nerdanderthal IDontLikeGooglePlus There is a Fix Old Cameras video under the Olympus Playlist that demonstrates a diode and battery contact repair on an early version of the OM-1. Thank you for your comments and interest in FOC.

First note that the Depth of Field button on the ST801 can be locked by turning to the left. However if there is a malfunction, the ST801 mirror box is not attached to the front plate, so the front plate can be removed to access the stop down button without any major disassembly. The procedure could be covered in a Fix Old Cameras video. In the mean time check the lenses for a manual diaphragm setting for stop down metering. Also note, that the open aperture feature of your camera makes its M42 screw mount non standard and when using a non Fuji lens you may have difficulties when trying to focus at infinity and also possible is the lens could get stuck on the camera.Thank you for your continued interest and suggestions.

Maybe one day.

The 1N34A should work. phototronic.biz/tips

The Pentax H1a and the Spotmatic line of cameras are all very similar in mechanical function. The camera in question is need of general service and to do properly requires a fair bit of disassembly. However the tension on the shutter springs could be increased to overcome the present inertia of the shutter curtains. The tension points can be accessed by removing only the bottom cover. This procedure is fairly simple and could be covered in a Fix Old Cameras video. Thank you for your interest and patience. As always, suggestions are greatly appreciated.

Thank you for suggestion and interest in FOC.

Thank you for the suggestion as it would be a fairly easy effort as there is room for the modification under the bottom plate.

@@FixOldCameras I opend mine and I got a 1N34A diode ready. But there are 3 (!) red cables going away from the battery compartment... Can you help? Don´t know how to contact you from Germany as my spoken english isn´t to good to phone you. I would like to make a video of the mod for your channel (free of charge of course)...

@@gun_flyin hi. i have a leicaflex sl but mine have only 2 cables. anyway... the sl have adjustment knobs hidden under the leather on front of the prism. you can calibrate your meter with them, no need to phisically modificate the camera. at least, mine work just great ant it's accurate

@@Fabio-id7jz thx I will give that a try 👍

Typo - it is ECG109

As long as the meter is working properly before the diode modification the meter will be as accurate after the modification with a 1.5 volt battery as it was originally when it operated on a mercury battery (1.35 volts).

@@FixOldCameras Thank you for the swift reply !

+Joseph Greenberg It is. The ECG 109 diode is now considered a vintage diode. It does still have limited availability. Any equivalent germanium diode will work as a substitute. In fact any diode can be tried, if the drop is incorrect try another, you will not harm the circuit.

Yes.

Thank you for the suggestion. It would be a good subject for an FOC video. Hard to say when it might be produced.

The diode modification will not fix a dead meter, but will make a meter that was designed to operate with the discontinued 1.35 volt mercury battery operate correctly with a 1.5 volt silver battery. It does so by dropping the voltage input from the battery.

thanks again. appreciate a lot you videos.

kettch42 The 1.5 volt battery will make the meter inaccurate but will do no short term harm. Using a hand held meter or another camera as a point of accurate reference the ASA can be adjusted to the point where the meter reading of the CL matches. Unfortunately this is not a linear adjustment and the meter will still be slightly off as the lighting conditions change. Most print film has an exposure latitude of one stop under and a three to four stops over, so you should be OK for the most part with the ASA compensation. Slide film is not near as forgiving. The button battery such as the EPX76 is readily available. But a small O-ring around so it fits properly in the battery chamber. The functionality would then be the same as the 625 battery.

Right on.

Not at this time, maybe in the future.

Fix Old Cameras thanks for the answer

@@FixOldCameras this link is no longer correct. Have an update?

@@Cheetorblz phototronic.biz/tips

Maybe... but at the very least the top cover will need to be removed for an inspection of the meter circuitry.