I got this meter cheap, in non working condition. Turned out the cable from the battery chamber was disconnected. The solder was eaten by battery acid.
First we have to remove the aluminum plate underneath. Its glued. Carefully use a wooden toothpick or something soft & sharp to pry it open. Then remove the screws, except 2 screws marked A. Those 2 screws has retaining nut , so can’t be removed right now.
Step 1. Case dismantling
If you just need to calibrate the meter, this is how far you need to go.. Just use the 4 trimmer at the bottom.
For a complete strip down you need to remove the aluminum scale. Remove the 2 screws holding the needle limiter (B). Remove the pin from the rocker switch (B2), so you won’t lose it. Slide the plate carefully. Try not to touch the needle, its quite fragile.
Now remove the 2 retaining nuts (D) holding the board. Now you could access the whole board. During reassembly put the high-low selector lever (E) between the spring, then screwing the board to the back cover.
The 2 screws (D) are shorter than the other, make sure you don’t mix them up. Using the longer screws on these positions will short the plate, the needle will shot to the right all the time.
This is the back of the board. It is attached to the battery compartment by 2 cables. On reassembly make sure the zero adjustment slot (F) is engaged with the pin on the zero adjustment screw.