The 20mA range current measurement stopped working on my Cen-Tech multimeter. The other current measurement ranges still worked. I suspected a damaged current sensor resistor, which is about 10Ω. I opened up the meter and quickly identified a 9Ω resistor which was measured open. And the discoloration indicated damage, which was probably a result of overcurrent. A nearby 1Ω resistor also showed some discoloration, but was still intact. The resistor is of size 0805, which probably has a power rating of 1/4W or less. So the maximum current is 167mA at this rated power. The fuse is rated 500mA, which would not be able to protect the resistor. Once the resistor was replaced; it worked again and was checked against a Fluke 87 multimeter, the measurements are within 20uA of each other around 20mA, or 0.1%. When it is compared with a Fluke 87, the Fluke uses a 0.991Ω 0.1% 2.5W resistor for mA range current measurement. The maximum current is 1.6A, which is greater than the 1A fuse rating.
