Gossen Luna Pro sbc does not Null

[PaulDalex]

I myself after cleaning the coil have turned many times forth and back the wheel
I don't remember for sure, but I believe that the cursor is metal. Not carbon.
And No. I didn't ever try to disassemble the wheel. And I don't know how it could be done.

 

[HpS]

I myself after cleaning the coil have turned many times forth and back the wheel
I don't remember for sure, but I believe that the cursor is metal. Not carbon.
And No. I didn't ever try to disassemble the wheel. And I don't know how it could be done.

So, I must have meant to say, 'remove the Carbon from the metal strip'!

Since the past few days I think my meter is responding better. The noise of the potentiometer seems to be almost negligible. Last night in very low light, I found it was a little noisy and I was not able to Null it.

I am taking readings everyday, bright light and low light, but I have to now check for the accuracy of the meter reading. As I don't have access to another meter, at the moment, I compared with the inbuilt meter of a compact Leica I use.

The Gossen meter reads about 1 to 1 1/2 stops Over, compared to my compact Leica. That is, if I were to shoot at the meter reading, the photo would be underexposed by that many f-stops.

I am still trying to find how to disassemble the front dial, to clean the dust inside it.

On the photrio.com under - Analog Workflow Forums/ Lighting - (Gossen Luna Pro F disassembly Discussion in 'Lighting' started by nathantw, Feb 6, 2017.) it says, the complete front circular emblem screws off, counterclockwise.

I couldn't loosen it with my fingers, hence will need to find a way so as not to damage the surrounding metal ring!

 

[PaulDalex]

Have you seen my thread on a stock of Gossen parts on Ebay? Nobody responded. I hope somebody with a repair activity will get it.
Anyway my meter seems to be worsening.
Before giving up I decided to disassemble again and take precise measures on the potentiometer with my Mastech multimeter.
This will take time because I ordered batteries for the multimeter which wil arrive in a couple weeks.
I will post the results
Regards
Paul

 

[HpS]

Yes I did notice your thread on spares.
My meter seems to be on the road to receovery. That will be great and without having to disassemble it! Barely any noise last few times I took readings. Just have to now confirm its accuracy.
All the best for your repair. I hope it will workout.

 

[PaulDalex]

Success! Or how to fix a Lunasix F with jumpy needle!

I disassembled again and made a crucial discovery.
The potentiometer has not just one cursor.
It has two of them!
In fact the cursor on the coil is connected to the central prong by means of another cursor, which slides on a metal disk. You cannot miss it if you look underneath the coil cursor.
And the disk was very dirty! I cleaned that too, I reassembled and
BINGO!
The needle now zeroes perfectly smooth!

The meter compared to my digiflash is spot on.
In a way I bought it by mistake. Without time to study the product I thought that it is similar to a Lunasix 3, but without the mercury battery hassle!
After the purchase I downloaded the manual (Thanks again Butkus! How could film photogs survive without you!).
It is a completely different beast!
Do I regret the purchase? Absolutely not!
It is an excellent meter, especially, in my opinion, for studio.
Do I want a Lunasix 3 too? Absolutely! But this is a story to tall in another occasion.
All the best
Paolo

 

[PaulDalex]

How To Repair A Lunasix F With Jumpy Needle

How To Repair A Lunasix F With Jumpy Needle

I wish to add a few notes.
It would be essential to have a repair manual and schematics. I searched on and on the net to no avail. For some reason Lunasix 3 is better documented.
Otherwise to repair other faults or to recalibrate, if needed, would be almost impossible.
If someone here has the manual it would be greatly appreciated sharing it.
Also, given that Gossen has interrupted repairs and sale of spares many years ago, it would be essential to find sources for spares.
I think old Gossen meters are wonderful pieces of gear and, like any other beautiful vintage camera accessory, deserve to be given a new life!

 

[View Range]

...On the photrio.com under - Analog Workflow Forums/ Lighting - (Gossen Luna Pro F disassembly Discussion in 'Lighting' started by nathantw, Feb 6, 2017.) it says, the complete front circular emblem screws off, counterclockwise.

I couldn't loosen it with my fingers, hence will need to find a way so as not to damage the surrounding metal ring!

Try using a rubber suction cup.

 

[valdas]

Thanks for those instructions. It reminded me I have somewhere Luna Pro F which gone crazy and I replaced it with another meter. I should look and see if that is the same issue.

 

[HpS]

I wish to add a few notes.
It would be essential to have a repair manual and schematics. I searched on and on the net to no avail. For some reason Lunasix 3 is better documented.
Otherwise to repair other faults or to recalibrate, if needed, would be almost impossible.
If someone here has the manual it would be greatly appreciated sharing it.
Also, given that Gossen has interrupted repairs and sale of spares many years ago, it would be essential to find sources for spares.
I think old Gossen meters are wonderful pieces of gear and, like any other beautiful vintage camera accessory, deserve to be given a new life!

Cheers PD. Good to know your meter is well and kicking!

During the process of our exchange here, I also wrote to Gossen askingn them where one can find repair manuals. They were rather matter of fact and said they don't have any paperwork of their old models. I am not buying this story!!

Yes it would be good if someone had access to repair manuals it would help so many people worldwide.

All the best.

 

[HpS]

Try using a rubber suction cup.

A rubber suction cup as in?

 

[alexmuir]

I have 3 of these meters, but haven't used them for a while. The circular metal piece which has to be unscrewed is of quite small diameter, so may be difficult to find a suitable suction cup. The ones used for fitting and replacing spot type lightbulbs (GU10 type) might work. Alternatively, you could just press a piece of sticky rubber against it and turn. Household rubber gloves are a good option, but anything soft and grippy should do.
Alex

 

[MarkWalberg]

This thread has been very helpful. I have just got a Luna Pro SBC with the jumpy needle problem. I've followed the directions given here in hope f cleaning the potentiometer. I've got the back plate off, and I've got the 4 screws out that hold the back to the front. The description given above says that the fron and back should come apart at this point. In my case, the front and back are clearly loose, but the will not come all the way apart. They do almost come apart. However, there is something at or near the potentiometer that won't let go. Any ideas on how to get the front an back apart ?

 

[Bolo Kukus]

The manual is available online. I've mislaid mine somewhere in one of my (too many) computers, but I recall it was super helpful to me when I was learning to use the thing.

HpS has written good and wise advice. Me, I would never dare opening this meter or any meter to fiddle with it. They are sensitive machines, and you can easily do a lot of damage or even destroy it. Resist the urge to tinker promiscuously!!

My Luna Pro is by far my best Gossen meter. I have a collection of meters of various kinds, but the LP is the one I use most. Dead-on for most exposures after I figured out that it consistently eads a third of a stop under, which is also easily compensated for. It's the go to meter with my Leica iif which also exposes a third of a stop under. Easily compensated for with the meter dial.

Good German technology, one loves a culture which gave us the Leica, the Rollei and the Gossen.