Possible to fix old light meters?

Kawaiithulhu · Nov 22, 2014

From the 1940's era I've got a beautiful DW-48 but the cell is less reactive than normal, over 4 stops in bright light and it hates dim.
Is it possible to bring these back to life or is it doomed to be a pretty display piece now?

E. von Hoegh · Nov 22, 2014

Kawaiithulhu said:
From the 1940's era I've got a beautiful DW-48 but the cell is less reactive than normal, over 4 stops in bright light and it hates dim.
Is it possible to bring these back to life or is it doomed to be a pretty display piece now?

Google search "Quality Light Metrics".

Gerald C Koch · Nov 22, 2014

If it is a selenium cell one then you out of luck. Electronic types perhaps if you can find an equivalent cell.

Kawaiithulhu · Nov 22, 2014

They're selenium so I may be SOL (selenium outta luck), but it's cool that Quality Light Metrics is not very far from where I grew up in LA - I'll pay a visit when I decide what to do, thanks for the tip

John Koehrer · Nov 22, 2014

usually it's the contact of the cell to it's frame

Sirius Glass · Nov 22, 2014

I have a Tessina selenium light meter and I cannot get anyone to fix it. There are no parts.

bsdunek · Nov 23, 2014

As John said, it's often the contact to the cell. Disassemble and clean the contact areas, rubbing LIGHTLY, as the coating is very thin. Just rubbing with a piece of paper is often enough to remove the surface corrosion. A little glasses cleaning solvent or lens cleaning solvent won't hurt. It's certainly worth a try.
Additional info. here if it still doesn't work: http://elekm.net/zeiss-ikon/repair/meter-repair/

John Koehrer · Nov 23, 2014

bsdunek said:
As John said, it's often the contact to the cell. Disassemble and clean the contact areas, rubbing LIGHTLY, as the coating is very thin. Just rubbing with a piece of paper is often enough to remove the surface corrosion. A little glasses cleaning solvent or lens cleaning solvent won't hurt. It's certainly worth a try.
Additional info. here if it still doesn't work: http://elekm.net/zeiss-ikon/repair/meter-repair/

US paper money has nice coarse weave that's good for cleaning this and small magnets like shutter speed/release on newer cameras.

AgX · Nov 23, 2014

Otherwise have a try at substituting the selenium cell by silicone photovoltaic cell.

Kawaiithulhu · Nov 23, 2014

All good ideas. I think that since it is still sensitive to light I'll spend Thanksgiving break attempting a cleaning of the contacts before trying to figure out a sensor swap or sending it out.

bsdunek · Nov 23, 2014

I'm a mechanical engineer, not electrical, but, AgX, I don't know how you can substitute a selenium cell with a silicon photovoltaic cell. Not saying you're wrong, just don't understand. If that can work, please let us know. I have a couple of historic light meters I would get working if I could.

AgX · Nov 23, 2014

Others have done so. By cutting a Silicone cell to size (or even taking a similar size from a pocket calculator or such), mounting it in the meter and re-calibrating it.

jochen · Nov 24, 2014

Hello,
a silicon solar cell has a completely different spectral sensitivity than a selenium photo cell. To compensate for this difference maybe you would have to implement one or more filters in front of the cell and to completely recalibrate it. Maybe the adjusting resistors have to be changed to adjust the current to the galvanometer.

Mr_Flibble · Nov 24, 2014

The selenium cell will die pretty quickly if the protective shell of the cell is compromised. If the meter still works but has lower output than normal it is probably corrosion of the contacts.

I have replaced the Selenium cell with a calculator solar cell once, added a 1k Ohm variable resistor to fine-tune it to the circuit.

Kawaiithulhu · Nov 27, 2014

The operation was a success, but the patient stayed died.

And by died I mean that even with cleaned contacts and fresh re-seating of the element this old beast isn't very sensitive and runs 3-4 stops off even with the GE to ASA correction. Or to put in geek words: it's now very precise, but not accurate at all

With its box and manuals intact it will now make it into my shelf display.

wombat2go · Nov 27, 2014

I put a thread here some time ago "Vintage Spotmeter Refurbish"

Basically the project was:
-The meter housing and lettering were cosmetically OK and the sensor was OK.
-The electronics was non functioning,, the battery types were obsolete and the battery compartment was corroded.

1) Obtain data sheets as much as possible for the characteristics of the original sensor.

2) Measure the transfer function of the original meter and its scales.

3) Model the DC steady state in a circuit simulator, modelling the transfer function of the sensor.

4) Select a present day battery type of different voltage.

5) Design a new circuit on the simulator using a transistor voltage follower to allow the new supply voltage while holding the original sensor bias and driving the original meter.

6) Rebuild the electronics on a prototype board

7) Recalibrate using dslrs

The difficulties are :
In those old meters the designers might have made custom meter scales to handle the non-linearity of the particular sensor.

The cost to do the above. It can only be done on a hobby basis. The cost in hours to do the above was far more than the purchase price of a new meter.

In retrospect my project was successful. The meter is now fairly accurate with the possible exception of EV8 to EV10 or so where the transition from low range to high range occurs.

RalphLambrecht · Nov 27, 2014

I'm all for fixing rather than pitching stuff but this is too involved for average Joe.I recommend to buy a new meter(even used)and retire this one.

wombat2go · Nov 27, 2014

RalphLambrecht said:
I'm all for fixing rather than pitching stuff but this is too involved for average Joe.I recommend to buy a new meter(even used)and retire this one.

I agree.

If there was one type of old meter that was very popular, it might be worthwhile to design a "kit" of internals plus a procedure for average tech oriented photographer to update it with soldering etc , new battery type etc, while preserving the "look and feel" like I did with the old Pentax3/21.

However I see there were many providers of the old meters and photographers have their own preferences of them to this day as we can read on the various threads on the topic.

Happy Metering!

Possible to fix old light meters?

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