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Multimeter Problem.

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Please help. I have a second hand P.O. meter no 12 C/1. It is a moving coil meter. It reads o.k. on Volts but under reads on Ohms. The zeroing pot does not seem to work. A label inside states that it has thick film components. Why won't it read Ohms accurately? Can it be repaired.

Thanks,

Z.

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    Well Taylor Electrical Instruments Ltd of Slough was taken over by AVO Ltd. in 1958 , long before thunderbirds were go,  so your post  office meter must go back  a bit - perhaps you are older than you look ? if it predates  that merger.  more here 

    Joking aside, I think for badge engineering purposes and to keep the high and lower cost laboratory and portable/toolbox ranges distinct, the two names were retained for quite a while afterwards.

    In any case there are/were very few variations on the basic circuits used inside, though the exact ranges and so resistor values and switching arrangements vary a bit, and the mechanical form factor changed quite regularly.

    Mike

     

    PS basically the same circuit redrawn more obscurely from older manual

    CCT.pdf

    And the manual for the wrong model, but a nice explanation of the theory.

    127A.pdf

     

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  • 0

    Well Taylor Electrical Instruments Ltd of Slough was taken over by AVO Ltd. in 1958 , long before thunderbirds were go,  so your post  office meter must go back  a bit - perhaps you are older than you look ? if it predates  that merger.  more here 

    Joking aside, I think for badge engineering purposes and to keep the high and lower cost laboratory and portable/toolbox ranges distinct, the two names were retained for quite a while afterwards.

    In any case there are/were very few variations on the basic circuits used inside, though the exact ranges and so resistor values and switching arrangements vary a bit, and the mechanical form factor changed quite regularly.

    Mike

     

    PS basically the same circuit redrawn more obscurely from older manual

    CCT.pdf

    And the manual for the wrong model, but a nice explanation of the theory.

    127A.pdf

     

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