Any thoughts on an odd OM2 meter needle issue?

Hi all,

 

I've been repairing an OM2 (not n), and have an issue I've not come across before, in summary the meter needle does not move or respond to light, this is the same for n=both manual or auto mode.

 

Batteries:

New batteries tested with both auto and manual and the camera shutter fires at all speeds and settings

Exposure:

Although the meter needle does not move both auto and manual modes appear to correctly set the right exposure settings, however the needle doe not move or provide any feedback, the aperture and speed rings also have the right tension and recoils and have no obvious issues, this is also somewhat confirmed due to the camera appearing to expose correctly.

Meter Needle:

I've had a look at the needle, its not misshapen in any way and if I carefully move it backwards and forward there is also no resistance or anything preventing it from moving. The needle will also move very slightly if I set the speed and ASA to the extremes so there is a little life in it, if I adjust any settings again it drops to the floor

Wires:

All wires and solder joints are great, current is as expected.

 

My last resort was to fit a new meter assembly I have spare, but before I do this (as it involves a bit of faf)I wanted to understand if I have missed anything, as I say I've seen a number of these but this is a new issue and can only assume the meter assembly is faulty in some way?

 

Any thoughts kindly appreciated.

Nothing more fun than facing the world with a meter-less camera and overcoming the challenges and obstacles.

Hopefully OM guru john_hermanson_2 will come along shortly, and deduce exactly what's wrong.

 

Until then: are you saying the camera appears to set autoexposure correctly (you can hear the speeds change when you adjust aperture, ASA, re-aim the camera)? If yes, it may not be the needle itself but the CdS reading cells connected to it. CdS cells tend to expire from age suddenly, in many mid-'70s cameras. The OM2 has two co-operative metering systems: durable SPD cell that reads off the film making real-time adjustments during exposure, and more aging-vulnerable CdS above the focus screen that predicts what shutter speed the SPD cell will set, and reads it out on the scale (or provides manual center-the-needle guidance). If the CdS cells croaked, the needle won't move or indicate exposure, while the independent SPD cell pointed at the film might still provide accurate autoexposure. A test roll of film would confirm whether this is the case: if so, at least you'd know you could still use the camera "flying blind" in AE mode until you get it repaired.

Edited March 29, 2019 by orsetto

Hopefully OM guru john_hermanson_2 will come along shortly, and deduce exactly what's wrong.

 

Until then: are you saying the camera appears to set autoexposure correctly (you can hear the speeds change when you adjust aperture, ASA, re-aim the camera)? If yes, it may not be the needle itself but the CdS reading cells connected to it. CdS cells tend to expire from age suddenly, in many mid-'70s cameras. The OM2 has two co-operative metering systems: durable SPD cell that reads off the film making real-time adjustments during exposure, and more aging-vulnerable CdS above the focus screen that predicts what shutter speed the SPD cell will set, and reads it out on the scale (or provides manual center-the-needle guidance). If the CdS cells croaked, the needle won't move or indicate exposure, while the independent SPD cell pointed at the film might still provide accurate autoexposure. A test roll of film would confirm whether this is the case: if so, at least you'd know you could still use the camera "flying blind" in AE mode until you get it repaired.

Hi Orsetto,

Thanks for the reply, yes this is correct, auto exposure does seem to be working as the aperture changes, and also responds with the same aperture but changing the light source I'm pointing out, just no needle movement! My instinct tells me that this is probably working okay but alas no meter movement, although as you say I should maybe put a film through it and review the results.

 

I will take a further look into the CDs cells, as you say there may be an issue here, my only apprehension is that I've never seen these fail, yes a little unreliable in their ability and there is that quirk of holding exposure in memory, but you could be right, there is a first time for everything!

 

Kind regards

I will take a further look into the CDs cells, as you say there may be an issue here, my only apprehension is that I've never seen these fail,

 

You've been very very lucky then!;)

 

This is probably the single most common failure point in vintage cameras: dead meter function caused by expired CdS eyes. I've never owned an OM2, so can't speak to how long its CdS system usually lasts. But I have owned several OM1s: these do suffer CdS failure in the usual manner, in ways that match some of your symptom description (the needle moves only if you set extreme shutter/aperture combos). Most cameras use a pair of CdS cells, one on each side of the eyepiece (OM1/OM2 are set up like this). The failure pattern typically manifests as: one of the two cells dies first, leading to partial functionality with limited sensitivity and tendency to over or underexpose by two-three stops. Then the second cell dies, leading to completely unresponsive meter needle that only seems to move if the camera is set to four or more stops over/under exposure.

 

With some cameras, CdS death vs needle gauge failure is very easy to diagnose: they have a battery check that involves the needle moving to a specific point on the scale with a good battery (if it does, the needle gauge is fine and the CdS is definitely dead, if it doesn't the needle gauge is dead and you might also have bad CdS cells). Unfortunately the OM2 cameras use a separate light for battery check, so that simple diagnostic doesn't apply. If you can get the needle to jump any significant distance by setting the shutter speed ring to 1 sec or B at f/1.4, chances are its OK (a totally dead needle mechanism wouldn't respond at all to any input). Dysfunctional metering isn't often the result of a bad galvanometer needle indicator: while fragile in some respects, they're remarkably rugged once installed in a camera. I've rarely encountered such a failure unless the camera suffered an impact strong enough to jolt the needle bearing (dropped off a table, fell down some stairs).

 

Of course, the OM2 has a more complex metering scheme than most other 35mm SLRs: the problem could be in the electronics or wiring that feed the finder readout. not the CdS cells or needle gauge at all.

Edited March 30, 2019 by orsetto

Hi Orsetto,

 

Many thanks and certainly words of wisdom that I'll surely take into consideration.

 

Kind regards Steve

Well in manual whatever the meter does really doesn't matter. In auto the OM-2 (the Olympus way) has 2 metering systems. The meter needle (which uses the sensor in the viewfinder) is only to indicate the approximate shutter speed. The actual shutter speed is determined by the sensor in the mirror box reading the shutter curtain (for short exposure, the first shutter curtain has a pattern on it) or the film (in case of long exposure). So the meter can be completely dead and the camera still work perfectly.

Hi Bebu and thanks for the reply, with a test film I have found that the auto exposure is working fine, I still think at this point that for some reason the meter assembly is dead, not sure or how this caused but when I get some free time I will look to swap the meter with a spare to see if get a needle response back.

 

Kind regards