[plumbweiss]

I repair AVo 40's, 7's and 8's of all ages for a local calibration firm who usually send them in because they're out of 2006 NAMAS requirements for 16th edition instruments. Yes, they're still used by electricians, power supply authorities, schools and colleges all over the world.

The worst for repairability is the 70's version with the blue flexi pcb, these go open circuit or a minor overload can frazzle them. The cutouts go over-sensitive, the dust guards go brittle and jam swarf inside the movements. The hairsprings get buckled. Later versions have trimmed shunts and multipliers and these overload easily, germanium diodes go leaky, ac voltage transformers go open circuit. Switch contact arms fracture. The ohm zero pots go very noisy and are a pig to replace. Movement coils go open circuit. Later 8's had an optional DC-DC converter to produce 15V from the 1.5V battery, it fits where the 15V battery should go.

The older wirewound units suffer frazzled internal resistances, dry joints on the current shunts, open circuit oxide rectifiers, poor accuracy and weak magnets, fallen-in glass, bad tolerance resistance wire, broken trip springs/lost bearing jewels, dirty rheostats, poor battery spring contacts etc etc.

Not that any of them are unreliable, I've just repaired them as part of my living for years...as many as 10 a week for the last 18 years. We have all the diagrams for all the 40/7/8's .

Megger Limited (formerly AVO) still manufacture the model 8 but only to order, they are handbuilt and a snip at over 600 quid a piece.