FAULY MOVING COIL MULTIMETER (ALTAI HC-2020S)

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CarlH

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My old, but formerly very good. Altai moving-coil multimeter, model HC-2020S, has developed a fault.

The fault is apparent on DC voltage.

The 0 to 10 Volts DC scale seems still to work correctly (eg, for a 9 Volt smoke alarm dry single-use battery). This voltage is also displayed correctly on the 0 to 50 DC scale.

I need the 0 - 50 Volts DC scale to check the voltage of an (off the car) 12 Volt car battery. However, this voltage (at most, around 13 V) causes the needle of the 0 - 50 Volts scale to shoot up to the end of the scale (slightly beyond the 50 Volts DC maximum point - probably up to a limiting stop for the needle

The same behaviour happens with the car battery on the 0 to 250 Volt DC scale. The needle shoots up to beyond the 250 Volt point.

Is this fault due to a simple fault like a faulty resistor on the PCB?

If so, how do I find the faulty resistor (or whatever) in order to replace it/them?
 

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I know the temptation to repair an old meter like that is strong but in reality they are almost impossible without a schematic and a source of precision resistors. What has probably happened is one resistor has changed value but you will find it almost impossible to trace without a schematic showing values and another meter to check the component. The resistors in those meters were custom made to specific values, you won't be able to buy them in a store. With digital meters being far more accurate and so inexpensive, repairs are not a realistic option.

Brian.
 

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Hung Chang HC-2020 multimeter repair, I would check the divider string for a failed resistor R7 or short-circuit maybe on the rotary switch. You'll need another multimeter to check the parts inside. It's a strange problem though.
Schematic: https://elektrotanya.com/hc_2020.jpg/download.html#dl
 

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Thanks, Brian!

That's good standard advice, of course. Thanks for your rime.

However, a moving coil meter should show (by needle flutter) a rapidly changing (up and down) voltage. Digital meters can't, AFAIK, do this. I need that very rapid response to change, at least occasionally.

So can you, suggest a new moving coil voltmeter with a really clear dial, and which has a good reliability reputation? An analogue multimeter would be fine, but I don't actually need facilities such as as current, resistance, transistor test in addition to voltage. However, I do need a wide range of test voltage modes, so it will probably have to be a multimeter (or several single voltage meters!).
 

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