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Alberto
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 28, 2004 - 11:31 am: | 
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Hi, I've an Agfa Selectronic S in very good condition with a shutter problem.
When I fire it, the shutter stay open for long time (~10 seconds or more)and the battery test lamp light on.
The batteries are ok, when I remove them the shutter fires very fast (1/250?).
The exposure meter (CdS cell + galvanometer) seems working ok.
BTW, does anybody has got the user manual?
Thank you. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 28, 2004 - 11:46 am: |
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I don't have an user manual. But I have (more or less) succesfully repaired one of these beasts, i.e. I needed another junker to repair it.
In your case I think there is something wrong with the shutter circuitry which is located inside the lens barrel. I once started to write a repair article on the Selectronic S, but getting to the shutter circuitry is rather straightforward. First you have to unscrew the inner filter ring and remove the name plate. Then you have to separate the focus ring from the front lens cell and to remove the latter. Now you can remove a thin ring of springy metal to remove the shutter cover.
In your case my best guess would be changing the timing capacitor, it is located on the upper right of the electronic assembly. You can also try to clean the gold wire contacts which hit against some pins of the circuit board. |
Alberto
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 01, 2004 - 07:44 am: |
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Hi Winfried, nice have your suggestion again.
It sounds not so comfortable. Do you know if it's possible to find the circuit diagram, or something similar? The problem seems related to the timing of the shutter. It opens, but it doesn't release after the right time.
Usually capacitors (electrolitic ones)can short or open. But I have no idea how an electronic
shutter circuit of the early seventies was done.
Thank you, regards. |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, October 01, 2004 - 03:08 pm: |
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The Selectronic Sensor cameras work with with a TAA580 integrated circuit which was manufactured by Valvo. All I found about this circuit was a short description and a pin-out diagram showing that this is a comparator circuit with a power driver.
Basically one input of this comparator is fed via a variable resistor (to set basic timing). The other input is fed by the timing capacitor which (depending on the camera, I don't remember how the Selectronic does it) is either charged or discharged by the CdS resistor. As soon as the voltage reaches the threshold set by the variable resistor the shutter solenoid will be switched off and thus will close the shutter. The higher the resistance of the CdS resistor, i.e. the darker the ambient light the longer it will take to charge (or discharge) the capacitor, hence the longer the shutter open time is.
In case that the capacitor needs to be charged, maybe it has a short and its voltage never reaches the threshold.
BTW the circuitry is not so much different from the Yashica Electro35 circuit except they used a standard IC instead of a module composed of several transistors (or a special IC on the later Electros). |
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