Quote:
Originally Posted by Bill R
...Since most resistors drift up in value, there is usually no need to take a resistor out of circuit for an initial test.
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There are occasions where a resistor will drift down if it's the older phenolic-encased type. If the resistor's been running hot for a long time, the phenolic case will gradually char from the inside and create a conductive path around the resistance element. Most often seen in one and two watt units.