Gossen Luna Pro Repair Question
It's been years since I worked on the gray Luna Pros. I used to know everything about them. Now I can't remember the simplest thing. So here's my question: Does the meter switch turn the power on and off, or does it just untrap the needle for a reading? That is, is the meter "always on" and require a case to cut the flow of power?
Re: Gossen Luna Pro Repair Question
Re: Gossen Luna Pro Repair Question
Thanks. I've already seen that. As far as I can see it says nothing about the "switch" being anything more than to un-trap the needle so it can swing for a reading. It gives no hint that it actually opens and closes the circuit. Many meters are always-on and depend on closing the case or putting on the lens cap to run the photocell resistance up, efferctively stopping battery drain.
Re: Gossen Luna Pro Repair Question
That might be a Gossen design "feature." My DigiSix is always on.
Re: Gossen Luna Pro Repair Question
I don't know the answer, but you could jury-rig a circuit with a multimeter to measure current. You'd have to take the battery out and hook up some external leads to the battery and battery connections, and use the multimeter to measure current flow when trigger is depressed and undepressed. A big pain in the butt to do, but at least you'd be sure.
Re: Gossen Luna Pro Repair Question
According to a schematic I've seen, the high-low switch puts no power on the circuit when in the neutral position... only when in the low or high position.
EDIT: Here it is
https://learncamerarepair.com/produc...2&secondary=37
Re: Gossen Luna Pro Repair Question
Thank you Brian. Thr schematic is so small on screen I can't get a good look at it. But I am prone to take your word. The meter is off when the switch is in neutral, which is what I'd hoped. I just finished cleaning and calibration of it but didn't go so far as removing the circuit board from the rear case half. And you can't tell if there is an actual switch that breaks the circuit in neutral. This meter has no case. And if it can cut off, I prefer it with no case. Those Luna-Pro cases add bulk and they are awkward. You have to bend them backward to keep them out of the field of view of the meter cell. And since this meter is a beater anyway, I can just keep it in my pocket and whip it out and meter with one hand. I have a really nice Luna-Pro in a very nice case that I also had installed a 2.7V v oltage regulator in for two 357 batteries. I just hate the case. Too fat for your pocket and a nuisance. This junker meter with no case will be perfect for X-ray film with my 8X10 Horseman I modified to reduce weight, and the contractor's tripod. Nice to know I won't be burning up batteries if it just sits on the table with no case, or walking around in the sun.
Re: Gossen Luna Pro Repair Question
Download the articles and the schematics are a lot easier to read.
I agree about the case.
Re: Gossen Luna Pro Repair Question
Got it calibrated perfectly for 357 batteries that had some use on them and were down to about 1.45-1.47V. Since it has no voltage regulation, it will swing between about 1.3v when the batteries are near discard, and the 1.55 when they are new. I figure that gives me a 1/2 stop swing, or a wee bit more, either way. But X-ray film isn't Kodachrome. This should do nicely. Not bad for a free meter given me by a friend who didn't like a little grunge under the dial. I can't get the center button unscrewed so I can clean it, but who cares? I'm sure it'll get even more nasty as a dependable junker in the pocket. Couldn't get te battery test down from above the red zone because the pot was full clockwise. So what? In this meter, red zone will simply mean time to get new batteries. Just like red zone on a tube tester.
Re: Gossen Luna Pro Repair Question
I have good experience with these zinc-air batteries when substituting mercury cells in meters/cameras.
When I measured the voltage depletion profile I could see it goes pretty quickly from 1.42V down to 1.36V and steadily stays around there until it takes a rapid deep dive.
I am currently successfully using them (with appropriate adapters to fit) in a Leica Meter and Pentax Spotmeter III - and other PX625/PX675 powered cameras.
There is 4-6 month usage in them after activation. They should be removed when not in use or depleted.