Leica CL meter issue/circuit board access

[amaschas]

I've recently purchased a Leica CL that has (as expected) an issue with the light meter. Luckily, neither the cds nor the galvanometer appears to be the problem, but there does appear to be something going on with the circuitry that results in the meter activating intermittently. The battery tester button works fine and the meter is accurate when it works, but sometimes it just won't turn on, especially in the cold. I've done some poking around with a multimeter and I've noticed a few things that indicate that something might be up with the variable resistors used to adjust the meter.

I've measure the resistances of the parts of the circuit I can access, and the galvanometer is about 3kO, which I believe is correct. The circuit overall is about 26kO, which is way too high. On a few occasions I've poked one of the variable resistors and the resistance temporarily dropped to about 5kO, at which point the meter started working, so I think the issue is that something in the circuit is increasing the resistance between the cds and the galvanometer when the meter is active to the point that the needle won't move.

I have a few questions I'm hoping someone here can help me with. First, has anyone seen an issue like this with a CL, and were you able to solve it? Second, does anyone know of a good way to get access to the main circuit board with the variable resistors? Failing that, does anyone have a copy of the service manual they can share, or know where I can get a copy? Any help would be greatly appreciated!

 

[VictorM.]

The problem may be with the meter switch contacts. They're under the top cover, near the advance mechanism.

Some info and pictures: https://www.flickr.com/photos/rwrede/albums/72157659250533456

https://www.flickr.com/photos/animaux/albums/72157672469120774

 

[amaschas]

The problem may be with the meter switch contacts. They're under the top cover, near the advance mechanism.

Some info and pictures: https://www.flickr.com/photos/rwrede/albums/72157659250533456

https://www.flickr.com/photos/animaux/albums/72157672469120774

I did actually pull off the top and verify that the meter switch contacts are working correctly. I can see just from the change in resistance in the circuit that the meter turns on when I pull the advance lever away from the body, but if the resistance is too high the needle won't move. From what I can tell the resistance in the circuit needs to be around 5kO. Thanks for the suggestion and links though!

 

[VictorM.]

The circuit board seems hard to access but the adjustment 'pots' are under a cover in the film chamber. The cover is held in place with double-sided tape and is easily damaged. It's really thin aluminum. Here's some images from my files:

 

[amaschas]

The circuit board seems hard to access but the adjustment 'pots' are under a cover in the film chamber. The cover is held in place with double-sided tape and is easily damaged. It's really thin aluminum. Here's some images from my files:

I think the problem I'm having involves one of the pots—R4 specifically. My guess is that there's a bit of corrosion of gunk that's altering the resistance of the entire circuit. I've noticed that when the light meter is unresponsive, the entire meter circuit resistance is 26-30kOhm. But I can stick a screwdriver into the screw for R4 and wiggle it a little and get the resistance to drop down to its normal range, which is 5-10kOhm depending on the light hitting the sensor. This seems like a problem I could sort out quickly if I could access the actual board.

Maybe if I screw the R4 pot screw out entirely and clean it? I'm worried something will come loose on the board and be irretrievable if I do that though.

 

[kaspermail]

Hi any chance You found some way to repair it? I have similar problem with my CL. I think You just cant screw out any of the R3, R4, R5, R6 screws. I am trying to calibrate my lightmeter with Energizer alkaline battery? Maybe this cause the issue?