How to fix an AVO Model 8

[Oldfred98]

I purchased n AVO model 8 MK 11 which has the following problems

The glass has become detached from the case. How do I fix the glass without complexly removing the innards

The cut-out button will not stay down. How is it held down

Any help would be appreciated

[davyrocket2]

hello Fred I think its a case of carefully removing the movement as for the cut out . I have not done one but others on here can advise how

[pmmunro]

Fred,

To refix the glass you will need to open up the meter and remove the movement from the front panel. Some caution is needed as the high voltage terminals are connected to the rest of the circuit by long, pointed hexagonal posts whose base plate is easily broken.

There are two connections to the movement which need to be unsoldered; the movements fixing screws are two large cheese-head screws either side of the magnet. You must use either a non-magnetic screwdriver or a non-metallic shield to prevent a steel screwdriver being drawn onto the magnet as any impact could reduce its field strength.

Refixing the glass has been discussed at length in previous threads but my preferred method is to use an epoxy resin glass adhesive after thoroughly cleaning of the old tarry glue.

There are a number of reasons the cut-out will not hold and in any case the cut-out will have to be reset if the movement has been removed. In any event, given the age of the instrument, the brass components of the cut-out should be cleaned as tarnishing tends to make the cut-out stick. I polish the brass parts with Brasso and then clean them with isopropyl alcohol. Dismantling and reassembling the cut-out is delicate work and it is best to treat the screws as not being interchangeable as the length below the shoulder of each screw is critical.

It would be best if you had the service manual as a guide - send me a private message.

PMM

[Sinewave]

I've had to do this many times with some of the Avo's I've picked up. PMM's advice should see it sorted.

[The Philpott]

Once the meter movement is out you would also be wise to remove the 'ohms divided by 100' adjuster knob and clean up the brass shaft on it's back end. The functionality of the low resistance range depends on this being untarnished and making good contact with the spring leaf.

Dave

I assume you know that the cut out bottom only can be pushed and stay in its position when the AVo is on horizontal position

[Sinewave]

Originally Posted by Aitor Eneko

I assume you know that the cut out bottom only can be pushed and stay in its position when the AVo is on horizontal position

None of mine pop out in other positions.

[The Philpott]

Certainly if they are set-up very finely to 'hair trigger' level the cut-out will tend to nuisance trip when the meter is handle upwards, especially if the meter is knocked or placed down heavily. (Only one or two of mine are set-up this finely)

Dave