Measuring CDS Cells on OM2 (and other OM series)

[CámaraLiberada]

Help!! I have an Olympus OM 2 where the needle doesn't bounce back, despite the speeds auto-firing correctly. Reading other forums, this leads me to believe that the issue is the CDS cells (?)

It seems like they are a typical photo resistor, so should I just measure their resistance like I would any other resistor? If so what resistance value should they measure?

 

[koraks]

I expect it's covered here: https://learncamerarepair.com/product.php?product=2305&category=2&secondary=9
Without having looked it up (!!!) such cells generally measure in the 2k - 20k range or so, depending on type and illumination level.
Yes, you can measure these like an ordinary resistor with a decent multimeter. Note that the reading should be responsive to changes in light hitting the sensor.
I expect that the linked service manual covers the procedure to calibrate the meter.

 

[ic-racer]

I replaced the cells on a Nikon a while back .

The thread may be of interest to you.

Nikon F Photomic FTN Service

I just got a Nikon F with FTN finder. Also came with a 50mm 1.4 pre-AI lens and a 28mm pre-AI lens. What caught my eye for the auction was the fact that the camera was in a case! Usually a pro in the 1970s would not carry the camera in a case. I thought, maybe this one has low milage. Indeed...

www.photrio.com

 

[wiltw]

The OM-2 used Silicon Blue photociodes which create current when light strikes, not CdS resistive cells.

 

[ic-racer]

The Silicone Blue Cells in cameras are usually reverse biased, and not used in 'photovoltaic' mode. So they do act like a variable resistor; passing more current as light intensity increases.

 

[koraks]

The OM-2 used Silicon Blue photociodes which create current when light strikes, not CdS resistive cells.

It in fact used both: https://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/om2/htmls/index2.htm
The fact that the exposure times seem plausible given the lighting conditions suggests the Si-diodes are working A-OK, as those are used for the off-the-film exposure. So the idea that the problem is indeed associated with the CdS cells as suggested by @CámaraLiberada makes good sense. This of course does not exclude the possibility of the defect being not in the CdS cells themselves, but elsewhere in the circuit. Then again, CdS cells do have a habit of going bad esp. if the housing is compromised and moisture and air find their way in.

 

[4season]

Don't overlook possible faults with the galvanometer: They can become fouled with bits of magnetic debris, or simply go open-circuit. Easiest way to test is with a multimeter in continuity mode: The very low voltage and current ought to be enough to make the needle twitch.

 

[CámaraLiberada]

Don't overlook possible faults with the galvanometer: They can become fouled with bits of magnetic debris, or simply go open-circuit. Easiest way to test is with a multimeter in continuity mode: The very low voltage and current ought to be enough to make the needle twitch.

I will try this first. The client states the meter worked before, and I have not done any repair related to the meter, or even top access of the camera.