SQ: Measuring resistor values already stuffed?

SQ stands for stupid question... :grin:

I measure resistor values in an already stuffed board and they seem to sometimes be correct and sometimes be off. For example, I have numerous 56k resistors which I can identify by the colors but when i measure them by probing each side of the exposed wire from the resistor I get like 46k. Other resistors in the same board are right on...

I would imagine that if I measured the resistor directly I should get the proper read out no matter what. But this is not happening. Before I rip out the components I wondered is my assumption true. Will they read differently when they are stuffed and not stuffed?

Thanks,
Michael

Yes, to be absolutely sure you have to lift one end - you could be reading the resistor with another resistor or other component in parallel, which would give you a funky reading.

As mentioned, most of the time you will not get a reading of the resistor alone, but the value of the resistor in parallel with a bunch of other stuff instead. More imporant is that measuring resistors in a circuit can be dangerous, especially if the power is turned on. Your multimeter is putting out a small DC voltage to obtain the reading. The circuit in question may not like this voltage and your DMM may not appreciate the additional circuit voltage coming through its leads (erroneous readings and possible damage). You can calculate the resistor's value if you know the (constant DC) current passing through it and the voltage drop across (V divided by I = R --> ohm's law), but otherwise you have to remove one of the resistor leads and measure with the circuit off.

Thanks!

I went ahead and just unsoldered a leg and popped it up and measured it like that. It saves any error on my part. Unfortunately it did not solve the issue I am working on BUT at least I can mark that off the list

-Michael