If the multimeter breaks and I can't measure the voltage, what should I do?
Because multimeters generally have pointer multimeters and digital multimeters, so for this problem, it is necessary to analyze separately according to the type of multimeter.
One, pointer multimeter DC voltage gear fault phenomenon and cause
1. The watch hands have no indication
The common node of the switch of the voltage part is desoldered; the multiplier resistor of the minimum range gear is disconnected or damaged.
2. Some ranges do not work, but other ranges work: the changeover switch is not in good contact or the contact is burnt out; the connection of the changeover switch contact and the additional resistor are disconnected or desoldered.
3. Large error in small range, small error in large range, multiplier resistance failure in small range, such as variable value, short circuit, etc.
4. After checking to a certain gear, the multiplier resistance of that range is desoldered or disconnected when all gears fail.
Two, pointer multimeter AC voltage file fault phenomenon and cause
1. The pointer swings small and the rectifier breaks down.
2. The error is about 50% low. One of the full-wave rectifiers has been broken down.
3. The indication value of each gear is low, the performance of the rectifier is not good, and the reverse resistance decreases.
Three, digital multimeter DC voltage file fault phenomenon and cause
1. The DC voltage file fails
Check whether the transfer switch is in bad contact or open circuit;
Check whether the resistance connected in series with the DC voltage input circuit is open circuit failure;
2. The displayed value of the DC voltage measurement is too large
Check whether the resistance value of the voltage dividing resistor is equal to the nominal value;
Check whether the transfer switch has cascading phenomenon.
Four, digital multimeter AC voltage file fault phenomenon and cause
1. The AC voltage file fails
Check whether the transfer switch is in bad contact;
Check whether the integrated operational amplifier in the AC voltage measurement circuit is damaged;
Check whether the series resistor at the output end of the rectifier is desoldered or the resistance value becomes larger;
Check whether the filter capacitor at the output end of the rectifier is broken down and short-circuited.
2. The displayed value of the AC voltage measurement jumps and cannot be read
Check whether the grounding (COM terminal) lead wire of the shielding layer of the rear cover is disconnected or falls off;
Check whether the filter capacitor at the rectifier output end is unsoldered and open circuit or the capacitance disappears;
Check whether the integrated operational amplifier of the AC voltage measurement circuit is damaged;
Check whether the adjustable resistor in the AC voltage measurement circuit is damaged or in poor contact.
3. The AC voltage measurement shows a large error
Check whether the adjustable resistance of the AC voltage measurement circuit has poor performance;
Check whether the rectification element in the AC/DC converter circuit is damaged or has poor performance.
