Shutter repairs

Testing a shutter
The full-sized image has lots of annotations for you to check out.
The shutter on my SXVR-H18 CCD-camera broke after three years of use, so I e-mailed the manufacturer to order one or two shutter modules as spare parts. Unfortunately they didn't have any in stock, but a day or two later I received an email saying I've been sent a box with a few old shutter modules in an unknown condition. That box arrived today in a thoroughly crushed shape, containing five nearly intact shutter modules in plenty of bubblewrap. They were apparently from various stages of manufacturing as they were all fairly different. The structure was the same in all (obviously, as they are for the same camera) but the electronics (current limiters and a parallel caps), shutter blades and mechanism substrates were all different among the modules. This was going to be fun.

I made a small 2-pin test-harness for the motor power connector to check the electro-mechanics, quickly tested all modules and none worked properly (could be from the rough handling of the package). So I disassembled all the shutters and sorted the parts based on condition. After the sorting thru the pieces I came out with three busted motors (two are needed per shutter), three pairs of warped, uncoated shutter blades and three working shutter.I had enough one the good parts pile to build at least one, most likely three, possibly even four working shutters modules. I decided to build three as making the fourth would require a bit more tools than I had taken out for the job.

The test-rig for the assembled shutter-modules was rather simple and I didn't even take a picture of it. Just a wide rubber band (visible in above image, too) to keep the shutter from over-extending and the same 2 pin connector for power from the bench supply as for motor tests. Tapping the pin-header on the shutter opens or closes the blades depending on polarity, and the motion stops against the rubber band.

The image is from testing one of the refurbished shutter modules on the camera (I should probably cut a smaller bit of antistatic mat for the computer desk as well to be on the safe side). Although all three were just fine with my test-rig, at first only one of those worked on the camera it self. Once I re-measured a rough estimate on the actual camera shutter signal, I lowered my test-rig voltage to 2.5V and limited the current to 60mA. With these I was able to repeat the performance on camera, and an hour or two later I finally had three fully functional shutter modules.

Out of curiosity I check the failed motors in more detail. The motors are small, 6mm diameter DC-motors with an equally tiny planetary gearbox. A shutter blade is press-fitted on the output shaft. Two of the broken motors were burnt or stuck and didn't turn at all, and the motor from my camera had it's planetary gearbox shred to powder, but the motor itself works just fine. I guess the cold winter nights can have an effect on polymers and they simply can't take the stress at low temperatures (below -30°C on clear winter nights).

In theory I should be able to rebuild one more shutter when the current installed one fails, and if these last at least a season each I should be OK till a proper replacement for the KAF-8300 sensor arrives. My requirements for a replacement are quite simple: no mechanical shutter, same diagonal or more, roughly the same pixel size. And a backlit sensor with better QE, especially on Ha-band, would be nice.

Now all that's left to do is to get a small bottle of argon, go to a clean place, recall how to completely clean a CCD-sensor, re-dry the humidity eaters and reassemble the camera in an argon-bath, so I don't have to worry about sublimated ice on the sensor surface.

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