Testing PreAmp Outputs

Wondering how to test the preamp outputs on my Alpine head unit. Im thinking when the negative and positive touched on the amp (fireworks) it shorted out the head unit. No bass since. Thanks much - Eddie

if it was fused properly it should have blown the fuse at the battery end.  Double check all your fuses at the amp and the fuse on the deck and under the dash.  Does the amp turn on at all? 

All fuses appear to be fine. The amp powers up but gets no sound. I tested with a brand new amp of my friends and I get the same results. The radio / Cd player still works though.. so i dunno, what do you say? can you stick a DVM in the preamps to test them?? just to see if sound is leaving the head unit. tnx man

you can scope for signal... you may have burned/fused open the audio ground path or may have damaged the pre-out OP amp ( although they tend to be pretty bullet proof)....Kevin Gerry

Certified Electronics Technician

MECP First Class Installer

Owner/Installer

Classic Car Audio

since 1979

Yes you can use a DMM to test for voltage coming from the RCA's of the head unit. Touch the positive test lead to the inside of the RCA and the negative test lead to the outside shield of the RCA, make sure you have your DMM set on AC voltage. It is best to play a test cd that plays a single tone, and then just keep turning the head unit volume up to and watch for voltage to increase. Jazzy

Jstruck, did the test.. im pulling .2v at max. Definatly fried the Preamp circuitry. sucks, ima get a new head unit soon though. thanks for the assistance