Olympus OM-2 with ASA dial issue.

[nickajeglin]

Hello,

I just got an OM-2 that seems to be in working order with the exception of some ASA settings. I get a mirror lock up if I set the dial to 250, 200, 100, 1000, 1250, or 1600. The shutter will also lock open and the iris will stop down as if it just froze in the middle of the exposure. I did wait several minutes to make sure that it wasn't trying to take a long exposure for some reason, and it seems that it's really locked.

The lock can't be fixed using the reset procedure in the manual (rotating the shutter speed ring to the *reset mark). It can only be cleared by switching the ASA dial to an adjacent setting. I'm using brand new SR44/357/303 batteries, and after I noticed the issue I double checked them with a multimeter.

The battery check indicator works intermittently, it seems to act like a touchy contact to me. That makes me think that maybe the ASA dial issue is also a switch contact problem. I've skimmed the service manual enough to know that the electrics run on very low voltages, so I could see how extra switch contact resistance could cause a problem. Hopefully this is a straightforward contact cleaning job.

Can anyone point me the right direction on where to start?

 

[nickajeglin]

Ok, so I dug into the service manual a bit more. Assuming I'm right about poor switch contacts, I think I'll need to follow the procedures starting on pg. 98. Has anyone removed the A cam to clean/diagnose the contact piece A, AR resistor board, and A cam?

Would it be a bad idea to do a minimal disassembly then go in with some deoxit D100 on the AR board/contacts?

Or am I on the wrong track here?

edit: I also see on pg. 127-1 that bodies mfg before '77 don't have an insulating washer between the AR stack's "A contact" and a lock spring. The symptoms are described as "shutter locked (mirror hung up and shutter will not run)". 127-6 also shows a ton of ways that the AR switch mechanism can short out. So that looks promising as well. I think I'll review the disassembly section to try and access the whole AR area to see how scary it looks in there.

 

[koraks]

the electrics run on very low voltages, so I could see how extra switch contact resistance could cause a problem

Voltage and impedance aren't related in the sense that a low-voltage circuit would also imply a low impedance. In fact, a camera from that era is typically a very high impedance environment so a little extra contact resistance doesn't matter much, or any at all. The problem is VERY MUCH extra resistance, which is actually quite common, since oxidized silver contacts (a common implementation) tend to have a very high resistance indeed.

Would it be a bad idea to do a minimal disassembly then go in with some deoxit D100 on the AR board/contacts?

The first part sounds good, but I'm always very hesitant spraying anything into a camera. It tends to end up all over the place, make its way into places you don't want it, fogging up viewfinders etc. Besides, if it's effective against oxidized contacts, who knows what kind of havoc it will wreak on front-coated mirrors, lens coatings, fine mechanics, old rubber etc.
Mechanical cleaning is usually a better idea IMO.

 

[monopix]

Never heard of Deoxit - just looked it up - that's expensive stuff. But I see it has a needle applicator so, if you're suggesting you can dismantle to the point you can apply some cleaner, in just the right place, using a needle applicator, then I would say that's OK. Just don't spray the stuff everywhere. And I would use IPA using a syringe which would be cheaper.

 

[koraks]

And I would use IPA using a syringe which would be cheaper.

It won't dissolve oxidation though. Will work OK on some other types of fouling.

The main thing is to not just use a solvent, but also remove it along with the dissolved muck. I often read about people just applying some contact cleaner etc. and call it a day, but that's literally a half-a&&ed job!

 

[Nicholas Lindan]

Try CRC contact cleaner. No residue. However, it lacks the 'snake-oil' appeal of Deoxit.

The prices for contact cleaners are divorced from reality so shop around. Contact cleaners are all made from

Naptha (AKA lighter fluid)
difluoroethane
IPA

(Deoxit adds it's miracle trade secret ingredient - some sort of red colorant that -will- leave a residue.)

Brake cleaner is an alternative, selling for a lot less, but it's a pretty aggressive cleaner and may attack some plastics. Made from tetrachloroethylene - the modern version of the old, and missed, trichlor.

 

[nickajeglin]

Thanks for the input everyone. I will definitely try some mechanical cleaning with IPA first.

Any tips on accessing the area in question?

Quick side note on deoxit: it has a pretty good reputation among the vintage stereo repair community as it will clean/flush/lube faders and potentiometers without destroying the resistive strips. The common belief is that it's naptha with oleic acid as the "magic" ingredient (plus that delicious red dye). Whatever it is, it does a pretty great job without destroying old plastics. I have a preference for CRC as well, but I got a bottle of the deoxit for an old amplifier that had no available replacement pots, so I was trying to be extra careful there.