Rachel's link is to an excellent and informative website, but it isn't the most user-friendly site in the world.
For me, as a one-time inveterate tinkerer (still am when my arthritic fingers permit) there's an important part that is very hard to find if you don't know where to look. It's the part that tells you how to get to the cell of a Weston Master II to replace it, and other useful stuff like that.
Start by going to the link given by Rachel
www.johndesq.com/westonmaster/ Right under the heading click on the bit marked Legal Stuff
Go to Item 7 and at the end it says Click here.
Do that and it takes you into the website home page with a lot of buttons down the left side.
Click on the fourth one down, Info+
This takes you to another page which starts with Exposure Meter Calibration
Scroll down this right to the bottom where you'll find a small line “JohnDesq's Bench”
This is a page about replacing cells in various meters. Click on it.
Scroll down till you come to the bit headed “NOT for the faint of heart”
Whew! Got there at last.
I used either these instructions or some very similar, I can't now be certain, some time ago to resuscitate a Weston Master II which I picked up at a camera fair very cheaply because it was as dead as a doornail. Take a look at the prices for replacement cells, let alone a complete overhaul. My resuscitation didn't cost a penny.
I left it in my photophernalia display cabinet for ages until a collector/tinkerer friend told me that in his experience about half the old selenium cell meters that are "dead" don't have a dead cell. They have bad connections at the cell.
So, nothing to lose. I could always button it up again and put it back on display. I took my screwdrivers and dived in.
PLEASE TAKE TO HEART WHAT THIS GUY SAYS ABOUT THE DELICATE NEEDLE. IF YOU BEND THE NEEDLE OR MESS UP THE BALANCE SPRING YOU MIGHT AS WELL JUST SCREW IT ALL TOGETHER AGAIN WITHOUT GOING ANY FURTHER. IT'LL NEVER WORK.
Having said that, it isn't really such a difficult job. On my Weston Master II I didn't find anything actually corroded, but the contact ring for the cell was covered in a thin film of copper oxide, almost un-noticeable. I cleaned it throughly with switch cleaner from Maplins (used to be Radio Shack) and cleaned the part of the cell with which it makes contact with a cotton bud (Q-Tip) just lightly damped, not wet, with isopropyl alcohol.
I put it all back together – being very careful to get the contact ring the correct way up - and IT WORKED!!
If you've got an old Weston selenium meter that doesn't work, have go. If yours is one of the 50% that doesn't respond to this treatment, just button it up again and keep it for display. Provided you're careful you've got nothing to lose.
Oh, I almost forgot. The guy mentions special screws. These are screws which don't have a slot or two holes to undo them. They've got a serrated edge to the head and I understand you need a special Weston tool to fit them, probably to discourage tinkering. I can't resist challenges like that so I drilled two small holes in the heads and used a peg spanner (peg wrench). They're covered up again anyway, so the holes don't show.
GOOD LUCK
PeterW
Maybe I'll try some "Wallage Surgery" on it! ;D
Roy