The multimeter rod is shorted, and the multimeter does not return to zero.
There are many reasons, from the outside to the inside, from simple to complex step by step.
1. Loosen the stylus and observe whether the starting position of the pointer on the left can return to zero. If it cannot return to zero, insert the nail into the bakelite at the root of the adjusting pointer to adjust the eccentric rod to zero, and the adjustment is unresponsive, and the internal small rod is broken. Can return to zero, put the ammeter on both sides of the desktop, stick it to the desktop and shake it left and right, and observe whether there is any obstacle in the middle from the left to the right. Obstruction means that the pointer scratches the dial or the glass. Take it apart and repair it. Accessibility, go to the next step.
2. Adjust the zeroing knob to the right, that is, the maximum zeroing correction. The red stylus touches the metal seat of the black stylus socket, and the black stylus touches the metal seat of the red stylus, which is equivalent to two probes connected in parallel and can be reset to zero, indicating that the stylus has poor contact, so check and eliminate it. Can't return to zero, go to the next step.
3. Disassemble the battery box cover at the bottom, take out the 1.5-volt battery, and put the multimeter at the DC voltage of 2.5 volts. Measure whether the battery has 1.5 volts. If it is not enough, replace it. If the voltage is sufficient, observe whether there is oxidation corrosion on the positive and negative shrapnel of the battery box, and if there is, remove it. No rust, adjust the shrapnel, enhance the contact with the battery, and install the battery. See if we can return to zero. Can't go back to zero, next step.
4, open the meter box, observe the zero line around the potentiometer center contact, with or without poor contact or potentiometer resistance wire broken. No problem, next step
5. Check the contact condition of the shift switch at the ohm position, and observe whether the switch has poor contact. No problem, next step.
6. Observe the small wire winding resistance of ohm x1 gear for burning.
If the first five steps are all normal, the problem is the sixth step. Usually, someone doesn't pay attention to it and mistakenly measures the voltage with the ohm file, which will burn out the internal small wire winding resistance and cause it to be unable to return to zero. Accurately match the resistor with the same resistance value, and the fault will be ruled out.
