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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 19th Mar 2008, 5:07 pm   #1
iainfsmith
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Default AVO Mark 8 Serial 39832C1055

I need help! Been giving good service for 35 years then suddenly expired, no ohms, amps, or volts dc or ac. 1.5 volt battery replaced meter movement appears quite free. Meter reverse button appears to have little or no movement. Clue? Can anybody help to bring an old friend back from the dead!
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Old 19th Mar 2008, 10:11 pm   #2
Leon Crampin
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Default Re: AVO Mark 8 Serial 39832C1055

Model 8 Mark? I would guess from the serial number it's a Mk II. If the movement reverse button feels unusual (they don't move far) then this would be a good place to look. As all the ranges are dead, the circuits around and including the movement need to be checked first. Are the cut-out contacts OK?

Leon.
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Old 19th Mar 2008, 11:18 pm   #3
pmmunro
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Default Re: AVO Mark 8 Serial 39832C1055

Iain,

The spelling of your name suggests Scottish origins in common with the inventor of the Avometer. As Leon suggests, it has to be a Model 8 Mk II with this serial number.

Several of us have written extensively on Avometers in this forum and there is other information on the web. Please read through the past discussions - most of what you need should be there. Above all you need a circuit diagram and probably another multimeter. The battery has no bearing on volt and current ranges in a Model 8; it is only used on resistance ranges.

I will be in limited circulation for the next few days but if you don't find what you need several other will be willing to help.

Please go carefully and research the subject well as your meter is delicate but worth treating respectfully.

PMM.
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Old 21st Mar 2008, 11:55 am   #4
iainfsmith
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Default Re: AVO Mark 8 Serial 39832C1055

Thanks for prompt replies - Have air-sprayed switch & cutout contacts but find Rev button inaccessible. Rev (metal) button immovable. What is the screw for? How do I check meter for continuity of coil? Iain of Aberdeen origin S.Uist

Last edited by Darren-UK; 22nd Mar 2008 at 1:32 am. Reason: Unnecessary quote removed.
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Old 22nd Mar 2008, 8:19 pm   #5
SPCh
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Default Re: AVO Mark 8 Serial 39832C1055

Do not, repeat NOT test the movement coil for continuity with a multimeter -
you'll almost certainly lt burn it out.

The only safe way is to use a low voltage (eg 1.5 volt cell) in series with a high resistance (eg 33k ohms) and a low current (eg 50 microamps) ammeter. Test the the current WITHOUT the meter movement in circuit first, and the ammeter should indicate around 45 microamps. Then include the movement in the loop and, if the coil is okay, you should get a reading on the ammeter of about 40 microamps - and hopefully some deflection (about 80%)of the pointer.

It sounds a bit "hit-and-miss", but it's the only safe way to proceed.

Assuming you get BOTH readings, the coil is certainly continuous with approximately the right resistance. Ohms Law will allow you to determine the exact resistance if necessary (PM me if you have a problem with that.)
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