DMM Help

[itchyfingers]

Hey guys,

I have a digital multimeter, but I don't really know how to use it.  I tried to measure the voltages of the beginner NPN Boost project using the black probe to ground, red probe to measurement point, and while I got values, they weren't even close to what was listed on the "Beginner Project Voltages" thread.  So I think I am doing something wrong!  If you had this DMM, which setting would you use?

[.Mike]

Hi itchyfingers,

I would...

1. Put the black wire in COM and the red wire in V-Ω (just like you have already done)
2. Turn the selector three clicks to the left from Off, to the 20 setting.
3. Black lead on ground, red lead on the test point.

BTW, here's the manual on your DMM: http://www.byramlabs.com/pdf/sperry/dm-4100a.pdf

I hope that helps!

Mike

[itchyfingers]

Thanks Mike,

I appreciate the help, and the manual!  Obviously I am a noob.  I set it this way and tried placing the black lead on the ground connection on my board.  Unfortunately, this nets me no readings across the entire circuit.  Could that mean I have a problem with my ground connection on my board?  Oh and this is weird, if I place the black lead on the negative battery terminal, I do get redings from the red probe throughout the circuit - is this what I am supposed to be doing?  The values aren't quite lining up with what's posted in that other thread, but I did change a few of the component values.

[aron]

Well, is the guitar plugged into the jack when you are measuring? The fact that you get readings when touching the black to the battery indicates that when you don't get readings, your ground is not connected to the battery negative.

[itchyfingers]

Duh, because the input jack completes the circuit!  Ok, I feel like an idiot.  Thanks for pointing that out Aron, I did NOT have the 1/4" in the input jack.  Now that I have, I am getting readings at all the spots on the "Beginner Project Voltages". 

One concern - I am getting the same voltage at the collector of the transistor as I am at the 9V.  Is that indicating something is wired up incorrectly?

[aron]

Collector right on the transistor or more towards the 10K resistor? Maybe you are measuring where the 10K resistor connects to 9V.

[itchyfingers]

Hmm, it should have been after the 10k resistor, as I was checking the solder joint of the socket that holds the collector.  When you normally check voltages, do you measure the solder side or the component side of the board?

Could it be my tranny is in backwards?

[aron]

I measure whatever place is easiest, but in your case, touch the actual leg of the transistor if you can - right where it meets the socket. If it's 9V, you probably have a short somehow. It should be less than 9V.

[itchyfingers]

Thanks again Aron,

I think by switching between the DMM and the signal tester, I'll get better at tracking these connection problems down!