Testing resistors while still in a circuit

[Gattopardo]

Is it possible to test resistors that are still in a circuit or do they have to be removed to be tested.  Searching some say yes and others say no.

What would you do?

[Feanor]

To test it properly, you'd need to lift one leg.

But sometimes you can deduce things.
Measuring in-circuit means there may be parallel current paths, and this will result in a lower than expected reading.
How much lower depends on what the parallel current paths are.

If the in-circuit reading is much *higher* than expected, then it's likely that *all* you are reading are the parallel current paths; it's an indication the resistor is open-circuit.

Resistors don't fail often, and when they do it's usually open-circuit with obvious visible charring.

[Kim]

^ This.

But if you have to do it, try your meter both ways round (on the basis that a device behaving as a diode in parallel will give you a spuriously low reading in one direction only).

My usual approach is to lift a leg or recruit someone with functional colour vision to identify it.

If it's tiddly SMD stuff, you probably have to remove the whole thing and try not probe it too enthusiastically and/or sneeze and forever lose it on the floor.

[Gattopardo]

The circuit contains a few riva x2 capaciators that have cracked so will be replacing those.  None have popped but am sure it is not far.

[Kim]

Capacitors can be usefully tested in-circuit with an ESR meter.  (On the basis that the impedance of a capacitor to low-voltage high-frequency AC is usually going to be lower than that of whatever's in parallel with it.)

[Gattopardo]

Capacitors can be usefully tested in-circuit with an ESR meter.  (On the basis that the impedance of a capacitor to low-voltage high-frequency AC is usually going to be lower than that of whatever's in parallel with it.)

Not bothering to even test them, just going to replace.