| Author |
Message |
    
William Martins
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 09, 2005 - 09:29 am: | 
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I have a Yashica 35 Electro G on which (long after acquisition) I recently removed the
bottom plate. I found some wires disconnected from the small circuit board next to the
battery compartment. One lead (red wire, battery + ) is directly off the battery compartment.
The second lead is white which I found out is the ground wire - probably from the battery
compartment also. There is a third wire (red) which, I suspect, is the lead going from the
circuit board to the positive side of the test lamp switch.
I need to know on what solder pads of the circuit board these wires connect to. There are two resistors connected in series: one has a value of 300 ohms (plainly marked) and the other is 700 ohms - I can make out the first color band, violet. So it looks like the lead coming
directly off the top of the battery compartment is connected to the pad holding the standoff lead
of the 700 ohm resistor. I' am basing this on the proximity of the pad when the circuit board
is mounted. The other two leads are up for grabs.
If some kind soul who owns one of these beauties wouldn't mind taking a peek and letting me
know how these wires connect, I would be deeply grateful.
Thanks,
Bill Martins |
WernerJB
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 09, 2005 - 01:48 pm: |
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Have just removed the bottom plate of my GS, but the design is different from what you describe, the resistors are printed to the white square board; when the circuit board is mounted, the red wire from battery plus is the closest to the front of the camera, the white one is connected on top of the board to where one of the resistors and the transistor (? three legs) are soldered together, maybe this helps, but I'm afraid I am not a very useful "kind soul", WJ |
charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 09, 2005 - 08:51 pm: |
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If you Google "matts classic camera collection" and go to rangefinders then Yashica you will see a picture at the bottom of the page that may be of help. |
charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 10, 2005 - 06:51 am: |
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Also see "provins.org.uk/" for schamatic of Yashica |
William Martins
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 10, 2005 - 08:09 am: |
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Hello Werner,
Thanks for your reply to this post. Your description sounds essentially like what I have only with different components. You say "...one of the resistors and the transistor (? three legs) are soldered together". I assume there are two transistors on your board. If so, and they are connected in series ( one after the other ), that would make up a voltage divider which helps stabilize voltage. If one terminal of the transistor is connected in between the resistors, then I would say that is the Base terminal of the transistor which needs
current across it before the transistor will conduct. So this would be a simple switching transistor. The output going out through the
Collector terminal to the Battery Test switch before it is distributed to the rest of the camera.
Anyway you more or less confirmed my thinking and I got a better idea of what to try. Thanks for your help.
Bill Martins |
William Martins
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 10, 2005 - 08:12 am: |
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Charlie,
Thanks for replying to this post. I've
been on both of the sites you mention and have
received help from both.
Bill Martins |
w-buechsenschuetz
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 10, 2005 - 02:22 pm: |
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The small board below the bottom plate is the battery test circuit. It DOES NOT work as a voltage regulator, which - btw - would not be possible without a proper reference voltage which can be set by a reference diode or IC only, but not with a voltage divider. If I remember correctly the circuit has one transistor only and is virtually identical to the test circuit of the Canonet QL17-GIII except for the thermistor which eliminates thermal drift (seet the repair manual section).
Similar to the meter circuit, Yashica used different versions of the battery test circuit. Older versions have a transistor and some resistors soldered to a board, while later ones come with 'printed' resistors. BTW this is what Yashica refers to as 'IC technology' on the Lynx14E/5000E - these ones do not use ICs in the meter circuit but a 'printed resistor' technology. |
Charlie
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 10, 2005 - 03:26 pm: |
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Are the wires broken or eaten through by corrosion? If the latter you may need to trace back to the battery compartment and throughout the camera to find all the problems. Good luck. |
William Martins
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 11, 2005 - 06:37 pm: |
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Hi Charlie,
The wires were broken off. Everything
is almost pristine as far as corosion goes. I think someone was tinkering with it and dismounted
the circuit board and/or battery compartment and
the wires came loose. There's not much solder
holding these connections and the wire size is
small anyway. I did a continuity check with the
meter testing the white lead on the board with
one in the test switch compartment and got a reading. So that looked encouraging. I'am waiting for a one cell AA battery holder so I can
bypass the battery compartment and apply some voltage to the circuit and see what's what. Radio
Shack doesn't stock them anymore. Thanks.
BM |
William Martins
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 12, 2005 - 10:30 pm: |
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w-buechsenschuetz
Thanks for replying to this post. First let me say the circuit on this camera is carrying two discrete resistors.
If you want me to send you an image of the exact board I can do that now. I never said anything about voltage regulation as you describe it. But I can recognize a voltage divider when I see one. And one of the benefits of such a system is that it has a steadying effect on the Voltage. You get that automatically. You don't need feedback and reference to accomplish this.
A second resistor, connected from the low voltage end of the first to the negative power supply terminal acts as a constant load for the first so that any variation in current from the tap becomes a smaller percentage of the total current through the first resistor. The heavier the current drawn by the resistors when they alone are connected across the supply, the better the
voltage regulation at the tap.
Also I get the feeling that this is one of the earlier production models. I don't think Yashica, at that point in time, would incorporate an elaborate system in the power supply that would drive up production costs. With the subsequent success of the camera in the market they could go to more sophisticated improvements. But early on it made sense for them to keep things simple.
Bill Martins |
Winfried
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 13, 2005 - 12:04 am: |
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Actually, you mentioned something about 'stabilizing voltage', but re-reading your post I see you did not say that the whole circuit acts as a voltage regulator.
Of course what you say about a voltage divider is correct, especially when the second resistor acts as a rather high load compared to the circuit's total load. However, in this case they simply make use of a transistor's base-to-emitter threshold voltage (I know it's not really a threshold), and in this case of course the voltage to be detected should be constant, so you can't do it with a single resistor from the supply voltage to the base. The transistor switches the battery test lamp on and off depending on voltage conditions. The big advantage is that you can detect voltages down to 1V or so, which was not possible using integrated circuits at that time (and still today ICs working at 2V and below are scarce). |
