(Another) analogue voltmeter does not go back to zero

[remzo]

Hi all

I'm using an ESP32 DAC pin to control an analogue voltmeter as a display. The voltmeter was designed to measure voltages up to 300V. I removed (what I think were) the resistors and connected the ESP32 pin output. The output produces a max of 3.3 volt. This moves the needle a little bit, but cannot move the needle to the end of the scale. Around 15V is needed to do so.

Also the voltmeter did not go back to zero. It stayed in a position around of third of the scale even if the ESP32 was disconnected.

I've 2 questions:
1. Is it possible to make this voltmeter work (as in control the needle around the scale) with 3 volts? Or should I increase the voltage of the output?
2. Is there a setting to 'reset' the needle to zero? I've tried the adjustment screw, but that is for much finer control.

 

[Ramussons]

1. Is it possible to make this voltmeter work (as in control the needle around the scale) with 3 volts? Or should I increase the voltage of the output?

Normally, about 50 - 100 uA is what is needed for full scale deflection, if it is a DC meter. Maybe there is another resistor in series with the coil which may have to be removed.

2. Is there a setting to 'reset' the needle to zero? I've tried the adjustment screw, but that is for much finer control.

Zero setting is normally Mechanical. Is there some mechanical damage? Bent Needle or dislocated Coil?

 

[For The Popcorn]

I recommend downloading a copy of The ARRL Handbook, 1975 Edition from this link and looking at the section starting on page 506 on descaling analog meters. This is an in depth discussion of everything you need to know.

Also, analog meters are precision instruments and won't withstand much (any) abuse, especially when out of their case.