Gossen Luna Pro F

[Chuck_P]

I will try those things in time, thanks all for the good advice. I was hoping for some kind of quick fix, but that obviously is not going to happen for me right now. I'm currently engaged in getting my darkroom back together and will need to focus time and money toward that goal. I will not give up on the Luna Pro F, until that time may come when I may totally botch the task with my completely uneducated tinkering with electronic circuitry.

 

[Sirius Glass]

I agree. Get some tools and give it a try. A couple things I’d add are that when soldering a connection, attempt to make a good mechanical connection first, such as twisting wires together, making a secure loop though an eyelet, etc. and then applying the solder. Also, keep in mind that the solder will run toward the heat so the iron goes on one side of the connection and the solder is applied to the other side and it will then run into that mechanical connection.

Yes, obtaining the correct solder is important. Don’t use the type used in plumbing. I use a 60/40 rosin-core solder that is .032” diameter for general electronics work. My iron is 25 watt. Occasionally I use a solder paste flux to clean the connection. Since removal of old solder is sometimes required, I use a solder sucker, essentially a spring-loaded vacuum. The only other tool I find invaluable is a “third hand” which is a heavy metal base that has an adjustable armature with alligator clips on the ends. It can hold the parts while the dolding takes place.

Like mentioned, this stuff is available at Harbor Freight. If one really gets into it, a “soldering station” with adjustable power, solder vacuuming system, lighting, and such can be obtained. It’s pricey.

Only use rosin-core solder. Acid core will oxidize and corrode electrical circuitry.

 

[eli griggs]

Only use rosin-core solder. Acid core will oxidize and corrode electrical circuitry.

And, just for fun, the OP can collect evergreen sap, say from backyard pines, and process it into his own rosin.

 

[Subversive Mk II]

I obtained a Luna-Pro F the other day, 'as is'.
A battery connector was destroyed, quite how the PO managed that, I don't know.
After fitting a new 9V connector and fly leads, I half-expected some results, but no.
It was quite intermittent, but at least there were signs of life.
I removed the back plate, removed the four long brass screws that hold the PCB in, then after careful inspection realised the PCB could lift out. What was still holding it in were the three tubular connectors inside that mate with three pins on the underside of the PCB.
I cleaned up the pins and tubes, gave a quick squirt of contact cleaner to the switches and put it back together.
Using a decent battery was able to get it registering something close to the L-P SBC I have, but I'll wait until I get a batch of fresh batteries to fine tune it.
So, looks like my ten dollar gamble might have paid off.
It looks almost unused, so that gave me some hope that problems were likely just old age and storage conditions may have just tarnished some contacts.

<edit to add>
Just fitted a fresh battery and the readings are within half a stop of the SBC, might tweak it a little bit, but might not.
The battery gauge pot definitely needs adjusted though - it shoots wildly off scale when tested.

 

[eli griggs]

Never forget that electrical wires, such as those that run from batteries or photocells, in the case of old selenium meters, can go bad beneath the coating, plastic or other types and replacing them at the same time you're fixing the meter, especially if you are not getting the full benefits of your replacement
of contacts, should be your next check out and replace as needed.

Good luck, we'll be looking forward to your final results.

Eli

 

[Bill Burk]

In a batch of meters that I got for repair, one of the best ones was a regular Luna Pro which had a factory battery conversion. The tip of the battery converter had corroded and fell out. After cleaning and soldering this bit of metal about the size of a happy face emoji

It’s now my first-check workbench calibration meter because it’s so accurate. I think it was recently factory calibrated. It reads correctly on my light standard and compared to the Sekonic L-758 across the whole range.

Definitely worth getting a proper 2.7 volt battery conversion for a Luna Pro.