Compur Electronic 3 shutter - what could go wrong?

[linhofbiker]

I just bought a Super Angulon 165mm from Germany. The lens is in a Compur Electronic 3 shutter. I have been told that these shutters are not reliable and can't be repaired. They run on an old 4.5v mercury battery but can be converted to CR123 with an adapter. I have 3 other lenses in Copal 3 mechanical shutters, so I could put the 165 SA in one of these some time in the future.

My experience with electronic shutters is limited to a Bronica GS-1. The Bronica lenses had a Seiko 0 electronically time shutter that was controlled from the camera body. These shutters never failed, were accurate and were silent during long exposures. I think the Seiko was designed in the early 1980's while the Compur Electronic shutters were designed in the 1970's or earlier. Have circuit boards, integrated circuits and solid state devices changed in that decade or so? The principles that guide an electronic "escapement" aren't that complicated I would think and therefore should be repairable or even replaceable. But I am an optimist and did have some electrical engineering training many years ago.

[Jim Galli]

I've never had one that didn't work. Have you applied 4.5 V from some source and given it a try? Cleaning electrical paths that slide against each other and checking for hard solder joints would be a place to start if it doesn't work. I wonder if an electrical diagram could be had for these. Mr. Salomon, can you help?

[Bob Salomon]

I've never had one that didn't work. Have you applied 4.5 V from some source and given it a try? Cleaning electrical paths that slide against each other and checking for hard solder joints would be a place to start if it doesn't work. I wonder if an electrical diagram could be had for these. Mr. Salomon, can you help?

Sorry, no. They were not available when I sold Linhof and our service center didn’t handle them.

[Havoc]

First you have to know what can't be repaired: the mechanics or the electronics? Some electronic components can go bad and are next to impossible to find or find a replacement that could fit. On the other hand, if the schematics and functioning are documented I'm fairly sure some enterprising hobbyist could put a replacement together. Likewise I'm fairly sure that if a correct mechanical piece is available, it could be remade.

[linhofbiker]

Thanks Jim. I have not received the shutter yet and was told it is working. In preparation for its sudden demise I have ordered an old repair manual about Compur electronic shutters, the 1 3 and 5, so hopefully there will be some circuit diagrams to aid in a repair if needed.

[MusicalPhotog]

I have a 300mm Symmar Conv in one... Works quite well. But I have noticed that the time does seem to fluctuate with the voltage applied. For example when running it with a 3v CR2 lithium battery, the speeds sound like they drag a bit (comparing by ear with known good mechanical). So now I'm toying with the idea of wiring a battery holder that holds (3) AAA batteries, in series, for a total 4.5v, to see if that would make a difference. AAA batteries are certainly easier to come by than the 4.5v mercury cells. Has anyone else tried this? Any reason I shouldn't attempt it? (For example: mA value from AAA too high?)

[Gary Beasley]

I have a 300mm Symmar Conv in one... Works quite well. But I have noticed that the time does seem to fluctuate with the voltage applied. For example when running it with a 3v CR2 lithium battery, the speeds sound like they drag a bit (comparing by ear with known good mechanical). So now I'm toying with the idea of wiring a battery holder that holds (3) AAA batteries, in series, for a total 4.5v, to see if that would make a difference. AAA batteries are certainly easier to come by than the 4.5v mercury cells. Has anyone else tried this? Any reason I shouldn't attempt it? (For example: mA value from AAA too high?)

I wired an electronic compur up with two aaa in series, mainly because thats all the battery holders I had at the time and it worked great. I never checked the accuracy but seemed to time quite well just from observation.

[Havoc]

mA rating has nothing to do with this so it should be safe. What can be a problem is that the voltage over time is different. Mercury cells have a very flat discharge curve, their tension varies little while they are used and then go fast low at the end of life. Alcaline cells have more drop along their life compared to mercury.

If the shutter speed depends on the voltage, then a couple of alcaline cells and a small voltage regulator would be a better solution. Some low drop regulator could be used. But it would be best to first measure the current used during an exposure to make sure this setup works. If it actuates some coils, then the current demand can be rather high during a short time. And you have to make sure you can supply it.

[domaz]

mA rating has nothing to do with this so it should be safe. What can be a problem is that the voltage over time is different. Mercury cells have a very flat discharge curve, their tension varies little while they are used and then go fast low at the end of life. Alcaline cells have more drop along their life compared to mercury.

If the shutter speed depends on the voltage, then a couple of alcaline cells and a small voltage regulator would be a better solution. Some low drop regulator could be used. But it would be best to first measure the current used during an exposure to make sure this setup works. If it actuates some coils, then the current demand can be rather high during a short time. And you have to make sure you can supply it.

A really crude solution to voltage drift would be to use a higher voltage battery pack (2 cell lithium perhaps which would be ~7.2v) then attach that to a 4.5v voltage regulator. The only drawback is you would need a switch between the regulator and battery as it would tend to draw current even when not in use I suspect.

[aphcl84]

These are in my experience extremely reliable shutters that generally either work perfectly or not at all when something is wrong. They can run as per the manual on 2.5-6v power so battery compatibility is pretty easy to manage, I use a cr123 with a aluminum spacer for my shutters. The mechanics of the shutter are very simple and share a number of parts with the non electronic compurs so parts availability is not that difficult. And the electronics are also quite simple consisting of 5 small transistors, two capacitors, two variable pots and 22 resistors. All of which could be replaced with modern equivalents. The shutters do use a small amount of power at all times though so be sure to remove the battery box when not using it.