Harvesting meter cells from new cameras to repair Nikon F and F2 meters

[Paul Howell]

I have a FTN non working head for my Nikon Fs, it came with a silver F along a with standard non metered head from bodies I inherited from a friend who passed away. I had an odd thought, what are chances that a cell harvested from a working Yashica 300 or non working Sigma SD 9, shutter is dead but meter still work for the FTN head? As I recall the Nikon F head used 2 batteries so about 6 volts, close the a camera driven by a CR5. Or a cell from a shoe mounted meter?

 

[Chan Tran]

Both of these cameras have different type of sensor and not the Cds type in your Nikon F. It's better to get a brand new Cds cell to replace. You need to see the size and shape of the Cds cell in the Nikon F and of couse the resistance characteristic. If you want to convert to newer type of cell it's still better to buy a new cell and design the circuitry.

 

[4season]

It might work, but without knowing the parameters of the original part, or that of light meter circuitry, I'd guess that the odds of it being a good replacement aren't so hot. I'd rather start with a brand-new part, and work from there. A small number of CdS photoresistors are still available through sources like Digikey, and if you restrict your choices to just those with peak sensitivity within the visible spectrum, your choices are narrowed down even further. The form factors are likely to be different from the original part, so you may need to get creative.

Also, galvanometers fail too. I test these by first ensuring that they move smoothly (not fouled with debris), then touching a low voltage / low current power source to it's terminals. The Ohms function of a multimeter ought to provide enough to cause it to twitch, but if not, something like an SR44 camera battery can be tried.

 

[Paul Howell]

Both of these cameras have different type of sensor and not the Cds type in your Nikon F. It's better to get a brand new Cds cell to replace. You need to see the size and shape of the Cds cell in the Nikon F and of couse the resistance characteristic. If you want to convert to newer type of cell it's still better to buy a new cell and design the circuitry.

Are Cds cells still being made? I was thinking that the reason no one repaired F and F2 meters was that the Cds cells are not available. I need to take apart my FTN meter to see how it is made. I looked for a diagram for it could not find one.

 

[beemermark]

Are Cds cells still being made? I was thinking that the reason no one repaired F and F2 meters was that the Cds cells are not available. I need to take apart my FTN meter to see how it is made. I looked for a diagram for it could not find one.

Cds cells don't die. It's the resistor under the speed dial that wears away. See

 

[Wolfram Malukker]

CdS cells do die, but only when exposed to air. The more modern ones with epoxy potting live a long life, the older metal can with a window do degrade over time.

 

[Paul Howell]

So, it if the resistor that dies why is noone repairing them?

 

[Chan Tran]

Are Cds cells still being made? I was thinking that the reason no one repaired F and F2 meters was that the Cds cells are not available. I need to take apart my FTN meter to see how it is made. I looked for a diagram for it could not find one.

Yes you can still buy them like these

https://www.amazon.com/Photoresistor-Sensitive-Assortment-Resistors-Light-dependen/dp/B07M9P6357/ref=asc_df_B07M9P6357/?tag=hyprod-20&linkCode=df0&hvadid=693270340071&hvpos=&hvnetw=g&hvrand=4970986664823803156&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9026816&hvtargid=pla-835067387698&psc=1&mcid=113a4e11b9a03f0eb5b998d9fca90f52

 

[Chan Tran]

I found the service manual but to down load the manual I have to pay. But I can do a screen shot of the page with the diagram. The FTN finder has 2 Cds cells.

 

[Chan Tran]

Cds cell not being used for meter today because it's a poor sensor for meter not because they don't make them any more. They still use them for other applications where accuracy isn't important like light switch that automatically turn on when it's dark.

 

[bernard_L]

Your chances of finding a suitable replacement are, IMO, quite slim. Yes, the current-voltage response of a photoresistor is linear.
BUT various photoresistors differ not only by their sensitivty, i.e. conductance (inverse resistance) at a given light level. The resistance versus illumination curve is NOT linear. Or, rather, it is linear in a log-log plot, with a slope that is different between various units. This slope (in log-log) being less than one is welcome because a large dynamic range of illumination translates to a smaller easier to manage, dynamic range in resistance and meter current.

For those readers not mathematically inclined, and as simple example, a value γ=0.5 means that when illumination changes 100-fold, resistance changes only 10-fold.

Illustrating the slope in log-log coordinates, from: https://docs.rs-online.com/fb50/0900766b8001a9d6.pdf

Variation of that slope between sub-types, from :https://www.kth.se/social/files/54ef17dbf27654753f437c56/GL5537.pdf

Dispersion of γ values even within a well defined component model number:

 

[Paul Howell]

I found the service manual but to down load the manual I have to pay. But I can do a screen shot of the page with the diagram. The FTN finder has 2 Cds cells.
View attachment 381190

Thanks, this is helpful, once I have a cell that will fit I will need to find the right set of resistors the compensator resistor may be key. But once I change that resitor might need to change the others.

 

[reddesert]

The problem with these meters is generally said to be the resistive track wears out - the "functional resistor" in the circuit diagram. This is like the track of a potentiometer and not a standard electronic component you can buy. If it were just a question of replacing the CdS cells, then someone could probably try to replace the cell with another CdS cell and adjust some of the trimpots to get it to work over some range.

There are two CdS photoresistors in parallel. If one of them went bad, you would probably see slightly off meter readings, but the meter would work. It is unlikely that both would go bad at exactly the same time.

 

[BobUK]

Slightly off subject, I read of someone having a Selenium celled camera meter that was faulty.
They stripped a cheap calculator for it's solar cell, and used that to get their camera up and running again.

 

[Paul Howell]

The problem with these meters is generally said to be the resistive track wears out - the "functional resistor" in the circuit diagram. This is like the track of a potentiometer and not a standard electronic component you can buy. If it were just a question of replacing the CdS cells, then someone could probably try to replace the cell with another CdS cell and adjust some of the trimpots to get it to work over some range.

There are two CdS photoresistors in parallel. If one of them went bad, you would probably see slightly off meter readings, but the meter would work. It is unlikely that both would go bad at exactly the same time.

I think I will replace all the resistors. Next step is set up a work station so that I tear down the FTn head. Might to get a new soldiering iron with the smallest tip. I think I have all the tools. Getting the silicon bule out of the Sigma SD9 should be too difficult as I don't need to be careful taking it apart.

 

[Chan Tran]

I think I will replace all the resistors. Next step is set up a work station so that I tear down the FTn head. Might to get a new soldiering iron with the smallest tip. I think I have all the tools. Getting the silicon bule out of the Sigma SD9 should be too difficult as I don't need to be careful taking it apart.

If you can take things apart you can test the Cds cells and see if they are still good. And you can also determine their characteristic.

 

[Paul Howell]

I think I have the right equipment, I have pretty good multimeter, I need to set up a test rig so I can power the Cds with a light source.

 

[Chan Tran]

Reading the service manual I found the key of the meter is the FRE. It's not linear but rather logarithmic.

 

[guangong]

I avoid all of this bother by using the plane prism and a small hand held meter when present. However, I did enjoy reading the commentaries.

 

[Paul Howell]

Well I have plane prisms for both of the Fs, Not sure when the FTn head died and was a little surprised that Nole had one, he was always a incident meter kind of guy. At this point it is a matter of curiosity.

 

[SMD]

It is the carbon track that gets used up when the feeler scratches repeatedly on it. What I wonder is how nobody begun producing it as a replacement part. China do you hear me?