Testing components in a circuit

[bpalatt]

I'm new to all of this and I'm not sure how to test resistors and capacitors with my dmm.  Do i need to remove them from the circuit, or can i just touch the leads and get accurate readings.  So far, it seems to work with resistors but not really with capacitors.  Do I need to do something different with electrolytics than with ceramics.  Any help would be much appreciated.  
thanks,
Brandon

[Boofhead]

To guarantee an accurate reading you have to pull the part out.  Having said that, pulling parts out is as pain and as you have found sometimes you can get a good reading without pulling.    Given your new at this you won't be able to guess whether in-circuit measurements are are reliable by looking at the schematic.  I suggest you measure in circuit and if the value looks OK move on otherwise pull the part and re-check.  The idea here is it's unlikely you would get a good reading if the circuit was affecting the measurement but be warned the in-circuit reading might look right but is actually wrong - only you can trade the effort of pulling parts against accuracy.  Measuring caps in circuit is far less reliable than resistors - in fact I rarely do it at all.  In both cases you can get a valid reading with the meter terminals around one way but not the other - all that means is the circuit is affecting one of the readings.

something different with electrolytics

If you measure electrolytics with a meter you generally *have* to get the polarity right (in or out of circuit), with non-polar types like polyesters and ceramics you don't have to worry about it.

[petemoore]

in ckt resistor...if the R reading is higher...must be the wrong value resiistor...
 If it's lower it means either: a lower resistance path is found going through the ckt or the parts wrong...look closely at the color codes or pull it to get actual' reading...
 Sometimes pulling socketted parts makes a difference.. the schemtic shows these paths.

[Paul Perry (Frostwave)]

On the bright side, you only have to pull ONE end out!

[bpalatt]

Thanks for the help guys.  At least I know its not me or my DMM.

[Mike Nichting]

I am currently trying to check the caps in my amp with no luck. I have no idea what to do.
I am expected to see 300mV but I don't see anything like that.
Can anyone help me??
Do I hold one lead on ground and the other on the end I pulled out of circuit??

Thanks
Mike

[Boofhead]

I am expected to see 300mV but I don't see anything like that.

Measuring the voltage across out of circuit doesn't tell you much. You shouldn't see any voltage across the cap, well except perhaps for some voltage due to the cap being previously charged - that will fall to zero as it discharges and the value isn't useful in general.

All you can do is discharge it (so you don't get shocked) with a 100ohm in parallel, pull one lead out, discharge again (in case it has charged up again and so it doesn't fry your multimeter), then measure it on the capacitance range.

There's other tests like leakage and ESR but these aren't so easy to do reliably with home equipment - it's possible to rig something up but you have to understand all the possibilities to know if your measurement is valid.