Selenium meter repair

OK: here's a Web page on short step-by-step instructions. These apply

to the Zeiss Ikon Contessa, but can be adapted to most selenium cell

meters, provided you can get to the cell.<P>

 

I haven't opened cells of ... say ... an Olympus Pen or a Canonet 19

or some of the others. But this really is intended to show you that in

most cases, it's not the selenium cell, rather oxidation of the

contacts.<P>

 

<a

href=http://host.fptoday.com/melek/zeiss/repair/meter-repair/meter-repair.html

target=_new>Visit page here.</a>

I would love to get the meter on my Rolleiflex going again! Looks pretty easy to do on the Contessa.

Thanks, Mike

 

I might just be brave enough to try this. Would you also provide a list of the tools you use, including nomenclature and size. I hate it when screws get buggered by using the wrong tool. I think I can use my own fingernails. One more thing. If the selenium cell is indeed dead, where can one get a replacedment?

 

Thanks Mike, for your instructions. First class effort!

Kerry, RadioShack sells this 17 or 18-piece screwdriver set. It includes some Phillips-head and a couple of nut drivers and hex pieces too. But the slotted screwdrivers give you just about every range you need. I also hate to see damaged screw heads.

 

Everything else is stock. The Pilot pen is sold as Silver Marker or Gold Maker with silver- or gold-colored casing.

I also used a Sharpie metallic marker once, but the tip was slightly too broad.

Hi, Mike. Thanks for the info! One other observation...a few of the Japanese meters were open at the bottom or at one end (some Yashica, Olympus, Petri, etc). Any loose piece of metal which is magnetically attractive will end up inside, and this usually stops the rotating coil dead. More than once, I've found all to be just fine except for that.

 

Jon

Wow, thanks Mike for the easy to understand example.Is it pretty much the same on the Retina IIIc?

The Retinas used sealed meters, mostly made by Gossen. You can disassemble them, but they're more difficult to service because of that. And it seems that most meters on Retinas seemed to have weather the years better than the Zeiss Ikon meters. As I've claimed in the past, I think it's because the Retina meters are sealed, while the Zeiss Ikon meters are rather open to the air, allowing for much quick oxidation of contacts.

Would this work on my old Leicameter? My local technician wouldn't take it for free, saying they can't be repaired.

Damn, you're good indeed!

 

Thanks for the "instructions", Tito.

Thanks very much, Mike! Nice to know that what I thought was black magic, (getting these to work), was really brave exploration and common sense. New life!

... almost anything can be disassembled. The real challenge is in reassembly.

Ain't that the truth...I've been working on a Signet 35 for over a year. I still know where all the parts go, mostly.

Henry Scherer has a section on his web site about this "repair." See http://www.zeisscamera.com/First.html#IIImeterrproblem

 

The following is from Henry's site:

 

The IIIa Lightmeter Problem

 

There is a story going around through various web sites that there is a simple fix for a IIIa light meter that doesn't work. According to these experts the problem is oxidation of the electrical contacts to the photocell and that all one needs to do is to remove the cell, take a blade and scrape the contacts. This is supposed to restore the meter to normal operation.

 

The fact is that about one of every five IIIa camera I receive for servicing has damage to the cell contacts caused by scraping. This damage adds a fair amount of work to the camera servicing because it is necessary to repair this damage by polishing out the scratches and replacing the gold plating that was removed by the surface being scraped. Zeiss understood corrosion, and in most of their light meters the cell contacts were gold plated to eliminate the possibility of corrosion and to ensure long term good electrical contact. There is no need to scrape the contacts. Corrosion is the problem, but it is corrosion to the cell itself, and not to the electrical contacts. The following illustration of the ideal selenium photocell shows what I mean by this.

 

 

* C is a transparent thin layer of metal that is deposited over the selenium layer (B) that is deposited over the steel sell support (A). The selenium layer is made up of small crystals. In order to collect the electricity from all of them, a conductor must contact each crystal. The only way to accomplish this is to use a contactor surface that is so thin that light can pass through it. Over a long time (around 20 years) this layer oxidizes and looses its ability to conduct electricity. The result is cell failure.

* (E) and (D) are raised electrically conductive surfaces that are applied to the front and back of the cell. These are typically made of epoxy filled with silver dust. These are the surfaces the meter electrical contacts compress against when the cell is installed in the meter.

* Another problem that can effect the cell over time is that the selenium layer (B) is a special form of selenium called "metallic" selenium. Selenium can have several crystal forms, some of which are electrically unconductive and which will not generate electricity when exposed to light. It is possible for the selenium in a cell to begin to change its crystal form over time. This conversion process can be triggered by the cell being exposed to excessively high or low temperatures. Once started the conversion process will proceed and cannot be stopped. In most cases its progress is slow.

 

The cells in Contax IIIa cameras are all old. While some may respond to light, the meter cannot possibly be accurate or linear with an old cell in it. The only way to restore the meter to like new operation is to have a new cell installed in it. There is absolutely no substitute for this.

 

There are almost no workers who work on the Contax IIIa light meter. I am happy to work on them and am expert in restoring meters to full operation, even those which have been written off by other experts.

 

If your IIIa meter has a problem and you want it made right correctly please write to me.

I sometimes wonder if that forum isn't a disguised commercial advertisement playground for THE man who owns THE website in which He explains He is The Only One who can repair Zeiss Ikon Contax stuff. THE man here, THE man there... anyone who searches Google with "Contax Zeiss" keymords will find his commercial site on the 18th results page*. So, no recurrent free ad is needed here, in my opinion.

 

Mike made many efforts to let us know about the DIY tips, I assume he was not doing that in order to get another advertisement for THE man and THE website, wasn't he ?

 

*BTW, Rick's pages are found on the 10th and 11th results pages with the same keywords :-)

Thanks for the detailed info. I have several that need repair. What is the purpose of the marker pen line? Thanks again

Scherer's dogmatic rant reminds me of Seinfeld's soup nazi skit. Mike's illustrations clearly show that removing corrosion on the contacts improves the function of the light meter. He didn't say that it would always fix the problem or be 100% successful. Little on-board selenium meters are never going to give the photographer more than a starting point for selecting exposure values because of a whole host of variables. If you can do a simple repair that gets you close enough, that seems like a pretty good thing to me. Common sense doesn't have to be ruled out as a possibility.

I wouldn't want to use the selenium meters on any of my classics to set the actual exposure - I am a little more experienced than the person for whom such a meter was designed. All I want is for the meter needle to move, to demonstrate the function of the camera to the wide-eyed "what's that, a camera?" types. If I was restoring a camera to mint functionality, only for display or re-sale, it would be different. So far I haven't had a problem with any of the semi-auto selenium cell cameras such as my Olympus Trip etc. Maybe I'm lucky.

I've found that if the meter is lively, it's also usually accurate to within a stop. And for b/w or color print film, that's usually close enough.

 

Sluggish meters are more indicative of a bad cell and are discarded. I've bought quite a few Contessas (I have a weakness for the folding Contessa and folding Contina II). I ended up with some dud cameras, but the selenium cells were good.

 

So far, I've ony run up against one cell that was sluggish, which I replaced.

 

In general, if you use steel wool, you burnish the contacts (hence, you remove the oxidation). The line of metallic ink on the cell forms a nice conductive bond with the existing material.

 

It's worked pretty well for me, and I haven't had one fail on me since. However, it's only been three years, not three decades. So maybe in 10 or 15 years, I'll be "eating crow."

 

By that time, we'll all be shooting digital, because we know film is dead! (wink, wink)

 

By the way, I have no doubt that Henry Scherer's skills far surpass my own. Still, it's possible to revive the meter in many cases without expensive surgery.

Mike: who is your supplier for replacement Se cells?

Scrape away, if you choose. It's your camera.

 

Robert

A very good, very precise and quite unagressive scraping tool is the fiberglass rechargeable pen that was formely used by stenotypists to correct writing machines faults. They are quite easy to find in some bureautics furnitures shops under several brands like Faber-Castell or Staedtler. You can also find them online at Micro-Tools for less than $10.00 including shipping.

 

I can say in addition that if a gold plated contact has lost its gold, it will cost you much much less money to have it gold plated again by your local jeweler than sending it to THE repairman. Having a 1mm x 9mm contact track goldplated with 5?m gold thickness shouldn't cost more than $30.00 by an honest jeweler.

Here is a picture of this tool.

And a picture of the refill, available separately for $1.50 each (lasts quite a long time).

I highly recommend this tool, having used it myself with success for years. Of course, you have to stop scraping as soon as the oxydation layer is removed, not to remove the metal itself.

The small retaining clip is made of copper, not gold.

 

RadioShack in the U.S. sells (or used to sell) a similar tool. Works pretty well for cleaning up contacts, though the small tips tend to break and little fibers can be a pain to remove from your fingertip.

 

However, as much as I like it, it doesn't work on getting to the underside of that clip, which is why I like steel wool or something similar.