How do you check RCA Preouts for voltage?

I think my decks RCA pre outs (sub pre-out, and my speaker pre-outs) are shot... That or I am measuring them the wrong way with my cheap 30 dollar digital multimeter.   with the deck on, and the sub out at volume 2 of 5, and music level at 10.. I measure the RCA sub-out of the deck with a multimeter checking for Direct Current (set at 2 volts) and I get no reading..  I dont know I would expect the readout to move around rapidly from 0-1.5 volts.  I Put the postive lead into the center of the RCA plug, and the negative lead on the outside shell portion of the RCA plug.  Am I doing something wrong? or are my pre-outs dead?  I mean sub-out, and all the speaker outs?

IF I am testing the wrong way, anybody wanna chime in on the proper way how to check RCA plugs with a multimeter, thanks.

RCA's use AC voltage?? wow that's weird I never would have thought.  I'll try that out, and I will check for continuity as well.  Damn that is so weird?

I just did the experiment on two decks (one of which I know for a fact works).. and I was unable to get a Reading using DC with it set to 20 volts, on the RCA plugs.   When I switched it over to AC, I got some mixed readings..  IE when I put the positive multimeter lead into the positive part of the RCA plug, it gave me a reading of 1.40 without having to touch the other negative plug with the shell portion of the RCA..  I then put the negative lead of the multimeter on the positive portion of the RCA plug and that gave me a reading as well, but it wasnt as high, it was around .40 volts, compared to the 1.40 volts I got earlier. 

I dont get it?   Anybody wanna explain my findings here?    

I am thinking of burning a 200hz constant test tone signal onto a CD and playing that, and seeing if I will get any results using the DC portion of the multimeter.  I can only guess that the signal off of regular music is too random and too fast of a signal for the mutlimeter to pick up.. 

Anybody else want to experiment with me, and come to a conclussion of their own and post it on here as to their findings?

Why in the first place do you feel that you need to test the voltage on the inputs?  Is there a problem with the system?  Let the forum know...but to answer your questions:

A music signal is AC.  You can read AC volts on the RCA terminal after disconnecting it from the amp.  But you must be very careful when you do this...DO NOT short the pos with the neg, and that's easy to do with those meter probes.  You can very quickly fry the deck.

You must use a test tone sine wave for a steady reading.  The voltage will fluctuate depending on the frequency and the ampitude of the tone.  For the surest reading you will set the deck volume to it's maximum unclipped signal, use several tones in the range of the speakers that the input is feeding, and get your combined result from that series of tests.  And the tones should be recorded at the reference of 0 db.

A safer solution to finding this input is to read the AC volts at the speaker terminals of the amp.  The amp gain has to be set to the minimum setting, but all else I said above applies.  This keeps you from shorting the inputs and frying the deck, and will be close enough for gov'mnt work.

I linked to a tone generator in this thread.  The free version allows you to make 3 second recordings, but you can record 99 tracks on a CD, and so you can make your .wav files and record them over and over on the CD.  It works fine that way.