How to repair the mechanical multimeter AC voltage and current mode fault?
a) When the AC gear is placed in the AC gear, the pointer is not deflected, the indication value is zero or very small.
Check the rectifier components. If there is damage, replace it, and re-weld when there is a virtual weld.
b) When placed in the AC gear, the indication is reduced by half.
This fault is caused by the failure of the rectifier circuit, that is, the partial failure of the full-wave rectifier circuit becomes a half-wave rectifier circuit to lower the output voltage, and the rectifier component is replaced, and the fault can be eliminated.
c) AC voltage block, the indication value is out of tolerance.
It is caused by the resistance change of the series resistor exceeding the allowable error of the component. When the series resistance decreases, the insulation resistance decreases, and the changeover of the transfer switch causes the indication value to be too high. Conversely, when the series resistance value becomes large, the indication value will be made low and out of tolerance. Troubleshoot by replacing components, drying, and repairing the transfer switch.
d) When placed in the AC current block, the indicated value is out of tolerance, which is the change of the shunt resistance or the short circuit of the current transformer.
Replace the components or adjust the repair components to eliminate the fault.
e)When the AC is in the AC position, the pointer is shaken.
Since the shaft tip of the meter head is too loose, the pointer is not tightly mounted during the repair, the quality of the rotating part is changed, etc., because the natural frequency is just the same as the frequency of the applied alternating current, thereby causing resonance. This is especially true when the bypass capacitor in the circuit fails and does not filter. The troubleshooting method is to repair the header or replace the bypass capacitor.