SEI Photometer Selenium Cell Replacement

Bill Burk · Apr 7, 2016

I recently picked up an SEI Photometer where the battery had never been replaced.

The corrosion was so bad, that after scraping out the old carbon and zinc I felt like a coal miner.

The selenium cell was, naturally, shot. So bad that chunks were falling off of it.

But I had played with the idea once of making a solar battery charger and had bought a few flexible solar panel pieces. I had one left that fit in a cylindrical shape (after cutting it in half). A little wiring and soldering...

Presto. A replacement selenium cell for the part that can't be found anywhere. Just cut a strip of solar cell material and place it inside as a cylinder and wire it up (Positive goes inside, Negative goes to ground).

mike c · Apr 7, 2016

Bill, how do you know the the solar cell is going to produce the same voltage as the selenium cell. It would be nice if it works out OK.

Bill Burk · Apr 8, 2016

I don't know yet... I just shoved a flashlight in the barrel and the needle swung more than halfway.

The bulb mount was so badly corroded that I have some more work to do before I can mount a proper bulb (I have the right bulbs).

If anything I have more active cell area than the original design, and I assume the new cell materials are more efficient. So I'm pretty sure I will be covering up part of the cylinder with black paper because the needle will probably peg.

When it comes to final calibration, I'll just mark a new red line where the needle has to be to agree with another meter.

jeffreythree · Apr 8, 2016

It should work with some extra resistance in the circuit. I used this to fix one: http://thermojetstove.com/Autoeye/meter.htm . The part about adding a resistor is towards the bottom part of the tutorial.

Bill Burk · Apr 8, 2016

Well, I got the bulb/battery compartment assembled. The flexible cells must have lower voltage than the original cell, because the needle only travels halfway with the bulb at full brightness.

Bill Burk · Apr 8, 2016

Now it's together. It's working.

Bill Burk · Apr 9, 2016

A retaining clip holds the battery spring in the base, on the type with a microswitch, one lead from the microswitch is screwed to the plate where the battery spring is mounted. Unscrew and lift the microswitch wire and remove the clip and then you can see the interior and clean it appropriately.

The black button type has a switch contact point soldered to the plate where the battery spring is mounted. It might be dirty.

I wouldn't spray anything in since it's so easy to take apart. But if you like to leave it alone, those rheostats are heavy gauge resistance wires coiled into a cylinder... I think working it back and forth will improve contact. Not like the carbon-based rheostats that wear out... these wear in.

Bill Burk · Apr 9, 2016

Thanks silveror0,

Good stuff.

Update. These flexible panels do the job! They are suitable replacements for the original cell.

I was fiddling around and broke a connection on the flexible panel. The place where copper joins selenium is very fragile on these things. You get one chance to solder a wire to it. Tin the lead you are trying to connect and then press it to the copper connector, solder for the briefest time possible... there is a plastic covering you have to melt and then the solder will spread. At the instance solder spreads remove the iron.

So I took the extra strip you see in the first picture and tried again, very carefully. Made my second one better than the first.

Checked with the voltmeter and got plenty of voltage. Put it back together and now I have full needle swing. The original standard brightness mark is "near" where I get correct readings.

Bill Burk · Apr 9, 2016

After reading the directions that ASA 40 is supposed to be across from the mark... where I had 50... I moved it. Busted both thin clear bands in the process and now the red calibration line isn't right on. (I never expected the calibration mark to fall correctly - it was just a nice coincidence earlier).

Like all my repair jobs. I need to learn when to quit. It was better before I knew what was right.

Bill Burk · Apr 9, 2016

For reference, this is the kind of cell, similar to what I used... sliced down the middle with a pair of scissors.

http://www.flexsolarcells.com/index...ges/02-PowerFilm-Solar-Cell-Module-MP3-25.php

Cells like these are cheap enough that I would recommend anyone projecting on their SEI Photometer... to pick up at least three of them.

Bill Burk · Apr 10, 2016

silveror0,

Think nothing of it. A couple busted clear bands won't hurt anything. They are the thin ones and they are held in place by channels, so other than "knowing" they're split... nothing bad will come of it.

I agree that paragraph 2 item 4 should say something else, just a typo. I read "is set against" - and compared it to my other SEI and saw the one-third stop difference and felt it was important to move it.

I started to worry I did the same to you after giving you advice to work the rheostat... when I read that one of the top service needs is rheostats that are no longer serviceable.

My absolute favorite mod is using the dime-store gadget that lets me put an AA battery in the D-Cell compartment. Beats tearing the paper wrapper off a Carbon Zinc cell or using expensive, heavy Alkaline D-Cells.

Valentin Trandafir · Jul 6, 2021

Hello !
I'm Valentin, an amateur photographer who just bought a SEI Photometer that I find absolutely fantastic !
But, unfortunatly, there are some issues and I need help to (hopefully !) fix them.
To make everything more complicated, I'm not a technical person (but ready to try my best !!!) and my english is not so good.
Would you, please help me to fix this photometer ?
Eventualy, I can send the meter to someone for repair and service if you know such a person.

Regards,
Valentin

chriscrawfordphoto · Jul 6, 2021

Valentin Trandafir said:
Hello !
I'm Valentin, an amateur photographer who just bought a SEI Photometer that I find absolutely fantastic !
But, unfortunatly, there are some issues and I need help to (hopefully !) fix them.
To make everything more complicated, I'm not a technical person (but ready to try my best !!!) and my english is not so good.
Would you, please help me to fix this photometer ?
Eventualy, I can send the meter to someone for repair and service if you know such a person.

Regards,
Valentin

Here is the factory service manual for the SEI Photometer:

https://learncamerarepair.com/product.php?product=172&category=2&secondary=37

Bill Burk · Jul 7, 2021

If it works without dismantling you will be better off. For example if you can carry a regular meter and adjust the SEI to it (find a spot, read with your main meter, set the SEI to match, and then go use the SEI)… Then you should not worry that the needle doesn’t move. My replacement solar cell never really was any good.

Valentin Trandafir · Jul 7, 2021

Thank you both, Chris and Bill !

SEI Photometer Selenium Cell Replacement

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