Fix Old Camera: Gossen Luna Pro Battery Diode Update
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- Опубліковано 21 жов 2024
- PX 13 battery availability issue for the Gossen Luna Pro and Luna Six hand held light meter. This video shows how to update Gossen Luna Pro meters to accept and accurately function on modern 1.5 volt button batteries.
classic camera repair - www.phototronic...
A few tools and books - www.amazon.com...
Thank you for this video. Humongous help. My Luna-Pro did not have the diode, nor the sliding light diffuser. My battery compartment slotted coin cover was corroded shut and the chamber was spinning when I tried to force it open. After removing it, hitting it with DB Blaster, then white vinegar, then boiling water, I persuaded it open.
I did, however, have a small 6mm clear rubbery washer left over after assembly. Everything seems to be working fine. I just hope it's not some important pivot point washer.
Another nice video. Could you include a video on how to make the adjustments? I wouldnt be able to guess what each screw is supposed to do.
Maybe the easiest approach to calibration for a tinkerer is by exposing the meter to different light levels and successively adjusting the trim-pots. Small adjustments should be made working between light levels.
As a light source, you either can make an adjustable light-box, or use several white walls with different levels of illumination accessible throughout the adjustment procedure. Meter the light source with a known good meter to determine the levels you are working with.
Adjustment Potentiometers positions: Upper left by itself - P1. Left to right across the bottom - P2, P3, P4, P5
P1 (10k) is battery test current adjust.
P5 ( 20 k) is high light adjustment. (P5 is used when the nd filter covers the CdS LDR) CdS (Cadmium Sulphide) LDR (light dependent resistor)
P2 ( 75 k) is low light adjustment. (P2 is used when the CdS LDR is directly exposed via the lens)
P3 ( 10k) is low light meter shunt adjustment.
P4 ( 10k) is high low meter shunt adjustment
P3 and P4 probably need to be set near mid point.
In bright sun about EV 14 or so, with the dome on, (incident mode) and ND filter on, the CdS/LDR resistance is 520 Ohm.
Dark resistance is about 20 Megohm.
The battery current needs to be in a range 20 ~ 60 uA, which is just enough to drive a small signal schottky diode toward saturation, so depending on the diode voltage dropper placed in series with the modern batteries that now need to be used there might be an accuracy problem that should be adjustable if need be. Some times after a diode install update no adjustment is needed, if the meter was accurate to begin with and the proper voltage drop was achieved with the diode modification.
Thanks for the extra info, if I get brave enough to (potentially) sacrifice my old Gossen I will give it a try.
So if the battery tester lands on red that means the battery voltage is ok and the light meter read correctly? Or what exactly the battery indicator shows?
Adjustment Potentiometers positions for the Gossen Luna Pro / Six:
Upper left by itself - P1. P1 (10k) is battery test current adjust.
Left to right across the bottom - P2, P3, P4, P5
P2 ( 75 k) is low light adjustment.
(P2 is used when the CdS LDR is directly exposed via the lens)
P3 ( 10k) is low light meter shunt adjustment.
P4 ( 10k) is high low meter shunt adjustment
P3 and P4 probably need to be set near mid point.
P5 ( 20 k) is high light adjustment.
(P5 is used when the nd filter covers the CdS LDR)
CdS (Cadmium Sulphide) LDR (light dependent resistor)
In bright sun about EV 14 or so, with the dome on, (incident mode) and
ND filter on, the CdS/LDR resistance is 520 Ohm.
Dark resistance is about 20 Megohm.
The battery current needs to be in a range 20 ~ 60 uA, which is just
enough to drive a small signal schottky diode toward saturation, so
depending on the diode voltage dropper placed in series with the modern
batteries that now need to be used there might be an accuracy problem
that should be adjustable if need be. Some times after a diode install
update no adjustment is needed, if the meter was accurate to begin with
and the proper voltage drop was achieved with the diode modification.
Small adjustments should be made working between light levels.
As a light source, you either can make an adjustable light-box, or use
several white walls with different levels of illumination accessible
throughout the adjustment procedure. Meter the light source with a known
good meter to determine the levels you are working with.
This is good stuff. Is the table at the end the conversion with and without the ND filter in place? I imagine I do not have to re-assemble the meter every time I tweak it (and that is my guess the purpose for the conversion table, so that I can test the high range without the filter and leave the unit dissembled during calibration). Also the shunt adjusts the low end of each range, correct? In other words, it is the Y intercept and the corresponding pot is the slope (adjusted at the high end of each range). Also is the EV @ISO100?
Wonderful! ... What a fabulous find this has been. Thank you!
Thank you for your interest in Fix Old Cameras.
Do you happen to know the relative magnitude of the current for this circuit? I have several diodes to choose from and I want to know which would most closely give me the .3V drop for this circuit. Also, all this diode does is drop the voltage, so you would need to use a silver oxide battery, correct? Because this battery has the most level voltage output over time while lithium and alkaline show a steady decrease in voltage over their life (Correct me if I have my battery types all mixed up). So this decline over time would affect the meter measurements if I'm not mistaken. Last question, can you simply use #9 rubber o-rings as spacers for these button cell batteries or do they need to make contact with the sides of the battery terminal?
Silver oxide is the best choice of battery. The diode can be tried with no concern of damage until you find the right combination of diode. Rubber O-rings can be used to hold the button batteries in place. The battery cap is the positive contact the battery terminal is the negative contact.
Which pole does the diode belong on --- Pos or Neg.
I just bought a gossen super pilot cds, does the same diode work on that meter? Also, do you happen to know if I just adjust the voltage pot should I get the same result as installing a diode? Thanks in advance!
I have a Gossen Luna-Pro that I haven't used in a long while. It's been properly cared for and stored. The needle is seemingly stuck in one position and doesn't deflect, doesn't move, at all. I put fresh, correct batteries in it, and it didn't make any difference - the needle still doesn't deflect with switch engagement. The needle is stuck in the upright position, a bit to the left side of the battery calibration red mark on the scale. I haven't taken it apart yet, but would like to, just to see if there is something mechanical I could do to free up the needle. Any suggestions on what it may be? Thanks. Great video, by the way! I've read all the comments, below, too.
First of all thanks for all your videos.
I have a gossen profisix (luna pro sbc) which I am trying to calibrate. There are three potentiometers labeled P1, P2 and P5. Do you know how to calibrate those?
many thanks for the post, I did this and now its right on. Very good meter and a big enough dial.
Good to hear of your success.
Hello, can gossen sixtar be calibrated like this too?
I have a Lunasix 3 and I am about to do the same upgrade but on my model, but: THE RED WIRE IS THE NEGATIVE!
The position of the batteries is the same as yours with the + touching the screwing cap. If the diode must be connected to the positive that is the wrong wire. Please check with a multimeter with the 'beep function' which is the positive.
Online you can find another video where you can see an Italian guy installing the diode on a blue positive wire one the side (Mine is Yellow).
I had intended to fix a Gossen Luna Pro meter in this way, but before I got to that point, I tried zinc-air 1.4v batts to see how that worked and found that I am unable to calibrate the meter with any battery. The voltage adjust shows good and can be adjusted, but the needle will only swing within 20 or 30º at either end on either scale. Shouldn't it at least be able to zero in the dark? I can't get a full deflection at all. My question is just this: do you think something else is wrong making it not worth the trouble, or am I missing something simple because I'm unfamiliar with this meter? Thanks very much. I enjoy your videos.
By the way you describe the issues, it is possible that the travel of the galvanometer is restricted. Can you manually move the needle its full swing? Does the meter peg when full battery voltage is applied? The meter should behave properly when powered by the zinc-air battery substitutes and zero in no light or when shut off.
The needle swings free enough and seems to react to light, but only with a small deflection which I'm unable to adjust to anything like zero even with the sensor covered. I can adjust it to a hi value but can only reach a value perhaps 3 ev lower than that... or vice versa. Battery test works, meter zeroed w/o power; It doesn't seem like something mechanical to me...maybe a bad component? What happens when you drop these a few times? I wonder if something broke loose. I paid very little for this, so perhaps I'll have better luck next time. Thanks very much for your response.
By the results of the trouble shooting you have done, it does appear to be a circuit issue or a combination Cds and circuit issue.
Battery 625 this light meter gives you accyrate readings of exposure ?
The diode modification with the proper voltage drop results will make the use of the available 625 (1.5volt) alkaline battery fairly accurate. Although an alkaline battery is not an ideal choice for a light meter due to its slopping discharge rate. The batteries will need to be replaced before the discharge level drops below 1.4 volts. The silicon diode suggested gives acceptable results, but is not a perfect choice. If a different diode is found that works better it will be posted. There are also MR-9 battery adapters available, but be sure to get an adapter that has the voltage dropping circuitry.
I recently acqired an FTbN and it had a tell tale scratch from a clumsy top removal. I went ahead with 1.5v. Alkaline and of course it's fine. They're really cheap these days, so I will be following your work on my Luna Pro also.
Question:
I have a working Weston Master Universal, a working Weston Direct Reading, and a Master II with the Invercone which doesn't work, but I would prefer to carry. Were these photovoltaic selenium cells interchangeable? Could one go into another? Thanks.
A direct swap might work or you might need to add a resistor. Might require some experimentation. Let us know what you discover. There was a time when selenium panels were available and could even be resized. Silicone cell salvaged from old solar powered calculators can sometimes be used in conjunction with a resistor (maybe a variable resistor so it would be easier to tweak)
Hi I bought I bought a Lunasix 3 but im batteries were not available, i was wondering if I could send it to you for modifications?
If you are interested in possible repair... phototronic.biz/service
thanks for the video! I want to open up a Lunasix Pro but mine doesnt open after taking out the 4 screws on the back. It feels like it is being held back by the turning dial on the front. Any idea how I can open it?
By the way my problem is, that the turning dial doesnt move the neadle anymore..
Any advice would be greatly appreciated.
Hmmm... not sure. Maybe the issue that has frozen the dial is also interfering with the case separation. Maybe there is another case screw that was overlooked on your model... do not know of the location of such, but variation of design has been known to occur.
Thanks for the great video, have used a few of your tutorials to repair some vintage cameras and lenses I own. What would you say is an economical modern equivalent of the sk 3080 diode, or what should I be looking for? not too up to speed when it comes to these sorts of things. thanks so much!
Substitute for meter system voltage dropping diodes -
ECG109 - OA90
1N4007 - DO-41
1N4007 silicon diode usually will work the best in most two battery systems. The diode referred to as a SK3080 diode in the video should have been stated as SK3090 which is germanium and has a smaller voltage drop. You sometimes have to experiment with different diodes in particular the two battery systems as many have voltage regulating circuits already. - more diode information here phototronic.biz/tips
Experience shows a silicon diode has a voltage drop of approximately 0.7V(varying 0.1V depending on the sub), while a germanium diode has a voltage drop of approximately 01.6V - 0.2.2V. Making the silicon diode(1N4007) the preferred choice for two battery meter systems. Though germanium diodes(SK3090,OA90,ECG109) with a voltage drop of consistently 016V) is the best in the area of forward voltage drop in single battery systems they are increasingly hard to find and more expensive, the silicon diodes are cheaper and apparently easier to find.
Experience shows a zener diode is not a good choice for a substitute. A silicon or germanium, conducts in one direction only, whereas a zener diode conducts in both directions, but at different voltages.
In most application beyond the voltage dropping application an ordinary diode is used to rectify, using its forward bias characteristics, while a zener diode is used to regulate, using its reverse bias characteristics.
I just attempted this mod. I went through 2 1n4007 diodes and then tried a 1N5711 Schottky Diode. None of them worked. With the diodes in the circuit I was getting no current. Also my Luna Pro has different internals so I suspect it might be a later model. The + wire is blue and the - is just a bare wire. The wire is also quite small and was difficult to work with. The connection to the battery chamber is sealed so I had to cut the wire and solder in the diode to each end of the cut wire. Right now I have reassembled the meter until I decide what to do next.
I put two lr44 batteries in the battery compartment and the meter needle lands on the red bar. Does that mean that it's ok?
It is a good sign that you have movement, but it still will depends on how accurately it reacts to different levels of light.
Hello, thanks for the informative video!
I was wondering if you have any advice on working with the Luna Pro S. I opened mine up in hopes of it looking the same as in your video, but there wasn't a clear red wire going to the battery compartment - it actually seemed difficult to reach the battery compartment.
Thanks for any help!
Yes it is different, but the battery compartment can be reached. Find the connection to the positive battery chamber contact and place the diode between it and the contact. Also you might consider making or the purchase of a voltage dropping battery adapter.
Thanks for the quick reply! I'll poke around in it again tonight and see if I can figure it out, but if I can't I'll probably go with the adapter route. Thanks again.
Thank you. Im attempting this soon.
How to remove the dial? thanks！
Thank you, so much.
hello , but i need two diode or one ?
Great video I have a Gossen luna six and happened to me that it fall on the floor and since then the needle doesn't lock when i take a measure, like it is loose making it difficult to read. Can you explain me how to fix it?
The needle is locked on a reading via a clamping device that probably just needs a tweek back into position. You can see the lower edge of the needle clamp mechanism at point 2.14 in this video.
You are the man! thank very much for both of your fast responses, I will get some real tools and try later if I can fix the problem
A few good tools will help.
I wanted to tell you that I managed to fix the problem successfully maybe someday I even try to go with the diode update, for now Im already very happy with the achievement
Very good to hear of your successful repair.
So I looked up SK3080 and IN4007, one comes up as a diode and the other a rectifier. I am not an electronics guy so I dont know if this is correct or if I am misunderstanding something somewhere.
In this application they are acting as a voltage drop in a DC circuit, so they are completely interchangeable. In fact any diode that gives the needed voltage drop will work. Experimentation will not harm the circuit if you get to much drop or not enough try another diode. If you put it in backwards and the meter will not power up... flip the diode end to end. No harm.
Additional information that does not apply to this application, but is somewhat relevant, is when AC power is applied to a diode it will only allow half wave to pass and it blocks the remaining half (called rectification). Usually there are two diodes (or rectifiers) in a rectification circuit. Each diode blocks half wave but together they make a full wave.
Did you tried to open Gossen Profisix or Luna Pro sbc ?
The screws are also under the back plate.
@@FixOldCameras Yes,but I can not separate the front side. like it's still hooked somewhere else
What battery do you use?
The 625A batteries fit, but have a gradual discharge fade rate once they start to deplete, therefore yearly replacement is recommended. The S76 battery has a level discharge rate but requires a small rubber o-ring fitted around the circumference to keep the battery properly in place.
O ring wins, thanks.
hi can you make a tutorial on how to remove a canon a1 iso dial if it has become stuck, mine is stuck
The Fix Old Camera videos A-1 Top Cover Removal might help.
Would this work on a Sixtar
Type
Hand held exposure meter
Introduction
1966
Sensor
CdS (Cadmium Sulphide)
The diode voltage drop procedure can be use on any meter or camera that was originally designed to work with 1.35 volt mercury batteries. Finding vintage diodes is getting to be difficult. But some have been using modern diodes with good results. You might have to experiment with clipping different diodes in the circuit to get the results you are after. You will not harm the meter as dropping the voltage too much has the same affect on the meter as a weak battery.
But i can use the sk3090 on any of my slr? Like olympus om1, pentax sp ii. Thanks
Yes. It works excellent in the OM-1 meter system.
Great meter, i own 2!
Indeed they are. Double the fun!
Can I use sk3090 diode! Thanks
You can use the SK3090, you might not get the voltage drop you need for the double battery system, but you will do no harm in experimenting with different diodes. The SK3090 seems to work really well in the single battery systems. If the SK3090 does not give you the results you are after. Try locating SK3080 / IN4007 or the equivalent thereof.