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Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 280
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 05, 2008 - 12:23 pm: | 
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There was this Hi-Matic 7s which I got from ebay for close to nothing. It was said to be for tinkerers, but it turned out to be worse.
The shutter is intermittently inoperative, the self timer stuck. Film transport is blocked, RF out of focus. But the lens is fine. So I decided to repair it, starting with a closer inspection of the meter. A sad short test showed the meter was dead, dismantling it and freeing it from its housing revealed that the rear retracting spring (simultaneously this one is the electric contact from batt. minus) was loose on the axis and had to be resoldered. This is usually not possible because there is not enough space for the soldering tip. I gently (VERY gently!) moved the spring with a toothpick and tried to align it with the solderpoint on the bearing (which is glued on top of the meter coil, too much heat will definitely harm the glue!). This can additionally be done by shifting the insulating piece that holds the other end of the spring. (VERY slight bending of the small metal strip to which it is soldered is possible, BUT ONE HAS TO BE EXTRA CAREFUL, if you slip it means the end of the meter!) When this was done I chose my weakest soldering needle (12V, 8 watts) and just inserted it in the narrow gap between the light meter frame and the windings of the spring. It worked! Not at once, but after several attempts the solder temperature was just right and the soldering time long enough that the spring and the bearing could be joined together.
For those who want to try this operation: One has to make sure not to give the joint too much or not enough heat. Don't get out of patience, even if your time is limited. Soldering time, on the other hand, should be as short as possible. Work slowly and carefully, wherever you touch the spring it will at once attract any solder which can then never be removed again, because the material is so fragile!
Although I have tried this repair at least half a dozen times, this is only just my second successful approach.
With the meter working I am now going to tackle the other flaws. |
Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 282
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2008 - 04:27 am: |
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The Hi-M 7s is making good progress on its way to recovery. I have found another reason for the notorious Hi-Matic lens wobble disease: the outer part of the helicoil is screwed to the square lens carrier plate from the front with six relatively small screws, if they come loose the whole setup becomes shaky. Secondly (and probably more important) there is a steering plate that keeps the lens straight when focusing, its two screws (accessible only from the back of the lens carrier) tend to unscrew just like the two two crosshead countersunk screws of its companion piece on the shutter housing. With all these screws just half fastened or out of their holes the whole lens barrel can be moved in all directions. Tightening them of course requires a COMPLETE knockdown of the camera's major components.
If you find Canonets difficult, keep your hands off the older Hi-Matics, they are difficult by two!
In the camera I am currently working on one of screws rattling around in the body had managed to get to the meter where it had been caught by the magnet!
One thing leads to another, that is what may have caused the shearing off of the retracting spring.
N.B.: On dismantling the shutter a small brass gusset fell out, it goes to the self timer lever and sits right under the thin flexible steel dust cover; it puts the self-timer back to default position for some reason. |
Charlie
Tinkerer
Username: Charlie
Post Number: 146
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2008 - 06:48 am: |
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You can buy rear window defroster patch kits in auto parts stores which contain a small tube of conductive epoxy. I have used small dabs to attach wires to PC boards, no heat involved but a slow cure time. I used it on a Yashica Electro 35 with no problem. I butt glued two wires together for testing and found zero resistance across the joint. |
Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 283
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 08, 2008 - 07:36 am: |
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I have used this stuff myself on a Ricoh 35L and inside a pocket calculator board, but found its mechanical stability depends very much on how clean the parts are that are glued together. I was not too optimistic it was suitable for tacking down the spring. |
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