Canonet QL17 GIII ASA Setting behaves strangely

[bennowa]

Hi there,

I recently succesfully cleaned stuck shutter blades of my beloved Canonet. 🙂 Happily I put everything together again, only to notice a weired behavior of the ASA setting mechanism.
The ASA setting ring, while moving just fine, has no reaction on the metering needle any more. I can move the ASA ring, but the needle would not move - the setting is constantly at what must be ASA 400.

There is one exception though: At ASA 25 the metering needle suddenly adjusts to this film speed. At ASA 50 to ASA 800 is constantly on the same level. 😕

I disassembled, cleaned and reassembled the ASA settings mechanism around the lens tube but this did not help. It all looks fine, but I may be wrong. Now it's me who is stuck. Has anyone an idea or clue how to solve this problem and get the ASA settings system up and running again? The Canonet is arguably my best camera and I miss her dearly....
Thank YOU! 🙂

 

[Sonnar Brian]

The mechanism is mechanical, works by using progressively larger openings over the photocell as you increase ASA setting. It sounds like the metal ring with the openings is not properly in position with the lever used to change the setting. The ring has a hole that sits on a pin, been years since I opened one up. I would check that it is opening as expected over the cell, then take off the namering and position the mechanism if it is not opening as expected.

 

[bennowa]

Thanks, Sonnar Brian! Initially I also thought it would be a mechanical mechanism, just like you described it. But in fact (from what I can see) the setting is achived by an array of resistors. Move the ASA ring and the current runs through a different resistor.
The progressively larger openings over the photocell, as you described, are driven by the shutter speed settings. (it's an interesting setup as it is the other way round in many cameras...)

in the picture attached, you can see the pins that connect to the ring with the array of different resistors (ring not depicted here; Picture is not mine but copied from the internet; sorry...).
I checked every single resistor on the ring with a multimeter and they all produce reasonable results. 😉

Maybe there is some error in the electronic circuitery? Or a short that cuts the ASA settings ring out of the loop somehow?

 

[bennowa]

...any Canonet QL17 GIII experts here, who might have an idea whats wrong with the ISO/ASA mechanism?
Thank you! Any help is appreciated 🙂