Which components can be measured while soldered on a PCB board already?
If have ony an ordinary meter then you cannot make accurate in-circuit measurements because the other connections will skew the result, but such measurements are possible with specialised equipment.

Most technicians will un-solder one end of a leaded component it the need to measure it, as this is usually the hardest way to mess up the measurement.

With specialised equipment Any 2 terminal component that is not parallel with another can be measured in-circuit by nulling out the other nodes and measuring it's impedance.







simulate this circuit &ndash; Schematic created using CircuitLab

Here unknown Z1 can is compared against known R1
If both are resistors the comparison will be the ratio of the voltages

Za and Zb do not affect the reading because V1 is a voltage source, and current in those parts does not effect the voltage a proble A.  Zc and Zd do not affect the reading probe B is a virtual ground and thus Zc and Zd have no potential difference and so pass no current. the grounds on Za Zb Zc Zd may be applied with aditional probes (usually clip probes).