Gossen profisix light meter repair.

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awty

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I bought a bag of camera stuff and this meter along with other stuff wasn't working.
Just want to write a note to myself and maybe others who want to pull one apart and can't find any info on doing so. You need to desolder the three metal tabs going to the potentiometer as well as the 4 screws.
Wish I new that before. You don't have to take off the front dial and spend a huge amount of time getting it apart. It will come apart when eventually the three tabs brake.... oops.

Desolder 3x tabs in red section
Unscrew the 4x brass screws in yellow.

20220922_190359.jpg


Anyway once apart it was easy to see the connection to the needle become desoldered.

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Also while fixing make sure to be super careful not to touch the fine spring on the needle as it doesn't take much to get stuck then you waste more time trying to find out what else is wrong.

Resolver in red.
Delicate spring in blue.

20220922_172918.jpg


Now I just need to reassemble and hope it works. Would of been a quick job if I knew earlier how to get it apart.

20220922_173151.jpg


And the front disc just unscrews, the rest just pulls apart, parts had been stuck together on mine and took a bit to prise off.

20220922_163040.jpg
 

AgX

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Would of been a quick job if I knew earlier how to get it apart.

A standard issue with repairs of modern stuff. Moreover at quite some cases such knowledge would not bring you much further (when snapped, glued or welded together).
 

MattKing

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Thanks for the write-up.
For those who are familiar with the US branding of this meter, it is known as the Luna-Pro SBC in that market.
 

ags2mikon

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Thank you very much for the write-up and pictures. Bad solder joints. Sure is a big problem now days in every industry.
 
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awty

awty

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A standard issue with repairs of modern stuff. Moreover at quite some cases such knowledge would not bring you much further (when snapped, glued or welded together).

Actually would come apart easily if I new to desolder the three lugs on the potentiometer. I thought there might of been another screw under tge dial. There is a rectangle window for the task of desoldering. I think the German engineers design a very good product, then redesign so only their technicians can repair.
 
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awty

awty

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Thank you very much for the write-up and pictures. Bad solder joints. Sure is a big problem now days in every industry.

Yes, that's what I was hoping for easy fix once you can find the broken joint. The DMM was showing power everywhere on the back of the circuit board, so I new the problem was after the switch.
 

AgX

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I think the German engineers design a very good product, then redesign so only their technicians can repair.

But then strange enough Gossen meanwhile refuse them for servicing, with the argument of having no spares, but without actual knowing they would need unavailable spares? (Or do they refer to the aluminium cover...?)

Your example is best to contradict them.
 
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awty

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But then strange enough Gossen meanwhile refuse them for servicing, with the argument of having no spares, but without actual knowing they would need unavailable spares? (Or do they refer to the aluminium cover...?)

Your example is best to contradict them.

It's not cost effective to repair things, technicians want to simply replace the part and if the part is not available they want you to replace the whole unit. Especially if the unit is 50 years old.
I do the same in my line of work, cost of repairs can soon outstrip the cost of replacing.
 

AgX

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Well, as our forum shows some fellows, me included, stick to the Lunasix F or Profisx and just do not want a successor model that may be more servicefriendly.

As with many if not most of our photographic stuff, repair is more costly then buying a used sample. But often this does not deter people from sending something in for a repair.
 
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awty

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Well, as our forum shows some fellows, me included, stick to the Lunasix F or Profisx and just do not want a successor model that may be more servicefriendly.

As with many if not most of our photographic stuff, repair is more costly then buying a used sample. But often this does not deter people from sending something in for a repair.

I did notice while looking that there is a calibration schedule for it that I'm sure any technicians could adjust.
My meter came in a box of non working camera stuff, I had no idea of what the problem with the meter was and as it owed me nothing it was worth having a look to see if I could fix. Still haven't put it back together to check its accuracy. If it works I'll have a very good meter for no cost, if not it will join the box of other non working meters I have.
Looks like a very informative meter and l can see why you would want to keep using it.
 

ags2mikon

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I have been using them for over 30 years and have found them to be reliable and accurate. Some of the accessories are a little obtuse in use like the spot meter attachment. My wife calls things like this Lego's for big boys.
 

AgX

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Looks like a very informative meter and l can see why you would want to keep using it.

It merit is the nulling-scale, which allows you to "place" luminances deliberately at the scale.
 

MattKing

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That and excellent low light sensitivity.
As well as the accessories, even if they are confusing in some cases.
 

AgX

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Did you find any pots in there that are for calibration?

You see them behind the print board in the first photo: P1 and P2. After taking off the board you see the resting pots, indicated already at the traces-side.
 

AgX

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I did notice while looking that there is a calibration schedule for it that I'm sure any technicians could adjust.

What calibration shedule? I have not come across one so far.


I guess that P1 is for the lower end of scale and P2 for the upper end.
 

ags2mikon

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Maybe like setting up a radio receiver you send it a known signal strength and adjust the low side then the high side and then go back and start over. I think we would need some type of documentation.
 
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awty

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AgX

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There are several calibration manuals out there for the Lunasix resp. Luna Pro, thus a preceeding model.
Worthwhile reading nonetheless.

That model got for each range of the twin-scale two potentiometers, one for the offset, one for the slope. Only the offset ones are accessible from the trace-side of the printed board.
How this relates to the Profisix with only one range and two accessible and more hidden potentiometers, you would have to find out.
 
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There are several calibration manuals out there for the Lunasix resp. Luna Pro, thus a preceeding model.
Worthwhile reading nonetheless.

That model got for each range of the twin-scale two potentiometers, one for the offset, one for the slope. Only the offset ones are accessible from the trace-side of the printed board.
How this relates to the Profisix with only one range and two accessible and more hidden potentiometers, you would have to find out.

I think it's fair that you find out and let us all know. I will be waiting in anticipation.
There are three trim pots accessible from the rear. I have no idea what they are for. Thought the one in the front might be for the battery test, but didn't affect it.
 
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Put it back together and all seems to be working. Meter is very responsive, getting equal reading from my nikon f100 set to centre waited.
Have to wait for Silver Halides to do a video on how to calibrate.
This is the sequence for putting the dials back on for me next time.
Had to restick the nut in the back of the face plate. Cleaned old grease and reinstate new grease. Front emblem was scratched when trying to undo, was held in with locktite. The rest is self explained.

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20220924_113607.jpg

20220924_113824.jpg

20220924_114025.jpg


Need to fix a lite version with a non functioning LED.

20220924_120256.jpg
 
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AgX

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There are three trim pots [at the Profisix] accessible from the rear. I have no idea what they are for. Thought the one in the front might be for the battery test, but didn't affect it.
Yes, three. I overlooked P5.

No idea either.
 
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AgX

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So this way of calibating then is very different from that of the Lunsasix 3.


low, linearity, high

versus

offset , slope
 
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