I'll tell you up front that I wasn't able to fix this thing, so this is just going to be a peak inside.
The problem with this meter is that the needle won't move.
Removing the back
The Nameplate here is actually a plate (not a sticker), so we start by taking out the little screws located at 8 and 4 o'clock. (Leave the big zero corrector alone.)
Next, we have to get those two tamper-resistant screws out (located at 9 and 3 o'clock). I have a jeweler's screwdriver handle that happens to fit these screw heads nicely, so I was able to pull them out without trouble.
Removing the Front
Now the meter can be viewed from the rear. The elongated brass loop (center) is the zero adjust. The baffle can now easily be lifted out and set aside.
On the top of this (it's hard to see here) there's a black headed screw that needs to be removed. There are also two pins on either side of it, and they can be extracted with tweezers. They'll fall out on their own if you turn the case over, so make sure you take them out yourself rather than risk losing them. The pins help hold the back plate on. It's not a catastrophe if you lose one or both.
Next up, there are two brass screws with flat slots so they take a normal screwdriver, and threaded holes drilled in the center (where the screws that held the plate in place were). Back these two screws out.
Front Panel Removed
Carefully prise the front off. Do what I say, not what I do. I bent the needle when I removed this one (the photo here is after I straightened it again).
Another note: I had another Master II open once and it had a rubber gasket inside to help seal it. This one did not; I'm not sure if that's a feature they began with and ended before this meter was made, or introduced it after this meter was made, or maybe a previous tech had this open and threw it away.
This one still didn't respond to light. The meter movement was free but way, way off the scale (as you can see here), and not because I had bent the needle. I turned the zero corrector on the back and was able to get the needle back onto the scale.
I really did not have the setup this time to go through the electrical, so I'm not sure whether the cell is simply not generating juice, or whether there's an electrical break or a short somewhere on the meter. Another time.