Finding the value of a resistor in a circuit without detaching it from the circuit

[vishnu.mthss]

Hi,

suppose we have a PCB with a lot of components in it; and we need to find the value of a fixed value resistor in it.

the problem is, any colour coding that was on this resistor has disappeared owing to wear 'n tear and we can't desolder the resistor from the board, as we can't modify the latter.

we can use only a voltmeter, ammeter and a DC voltage source which can be connected to the board.

so how to find the resistor value??

i came across this question at a tech-fest and i'm still wondering about it.

please reply at your convenience

 

[chuckey]

If you apply an external voltage and measure the current, some of the current may not be flowing through the resistor but through any other circuit components that are wired across it. If you keep the voltage below .5V then silicon transistors and diode will not be switched on by such a low voltage so will not draw any current.
Frank