Expert: Cleggsan - 1/23/2010

Question
99 Jeep Cheokee.

My amp operation has been intermittent for a while, but now it has stopped working. Power light on amp is off. I used a multimeter to test voltage from battery power cable and the remote wires unattached to amp. I got good voltage readings (12v). I changed ground points and still got good reading (unattached to amp).

When I attach the wires to the amp, the remote wire voltage remains good (12v). However the voltage between the pwr and ground drops to 1.75.

I purchased a new amp and got the same results with testing. I dont understand why the voltage readings are dropping when I attach the pwr and grnd wires to the amp.

Anyone have any thoughts?


Answer
Depending on where you are attaching the probes of the vom,  it seems to me that you have a bad ground connection between the amp and the car chassis.  Sometimes that ground needs to be disconnected and the metal parts sanded down to bare, raw metal surface and reconnected in order to get a good ohmic connection.

Or, there may be a low impedance short condition somewhere in the wiring; it can even be in the speaker wires because the  "-" line on some amps connects to chassis, thus if there is a short caused by insulation penetration or something like that it can cause the problem.

Check the current being drawn when you connect the amp.  If the voltage drops that much there may be a dangerous amount of current being drawn.  Does the voltage at the battery drop to 1.75 also?  Check that and if the voltage at battery stays solid at 12 or 13 volts maybe you have other problems.  If the voltage drops at the battery maybe you have a high resistance cell in your car battery.

So, check more and I think you will find the problem.  But let me know if you need more.