Audio Systems: Car amp problem, sound fades, car amp

Question
Hello,

I've had occasional problems with my car stereo over the last year.  One time, there was a whine coming from the stereo that changed with acceleration.  This lasted a day, and the next day there was a loud "putt-putt" sounds from the speakers, which sounded like a lawnmower or a go-kart.  This disappeared, and then for a long time the stereo worked fine.  Then several months later, there was a loud high-pitched squeal that came from the speakers whenever the stereo was turned on.  It wasn't affected by changing the volume.  This problem disappeared after day.

Now, there is a new and persistent problem.  When I turn on the stereo, it seems to work properly - CDs can be loaded from the trunk-mount changer, radio stations come in.  But then after 30 seconds, the sound fades.  I don't any sound again until after the car has been parked for a while and I start it up again.

So, I've got the hint - my stereo system needs work.  I've brought it in to two places (a Best Buy and an independent mobile audio shop), and both places determined that the factory amp is blown.  I guess this makes sense.

However, they've told me two different things about what needs to be done.  The Best Buy person said that I must buy a new stereo/headunit, and then he will rewire the existing amp.  He made this determination without really inspecting the current system.

The independent shop person spent a little more time checking some of the superficial speaker connections, but came to the same conclusion about the amp.  He told me that the amp needs to be replaced (not rewired), but that the headunit and CD changer can stay.

I'm comfortable with the diagnosis of a blown amp.  What do you think is the most appropriate way to get this fixed?

Thanks for your time.

Leland

Answer
It seems to me the system installation from the first time it started acting strange had a loose ground wire, power wire or some such condition.

The whining and squealing sounds are typical of localized problems with the power amp.

However, the fact you get sound, even for a little while, after the car has rested, means the amplifier is really okey or just needs some tuning up.

OR, it could mean during the symptoms over time that you described really did take both the head and the amp out; but I doubt it.

Look, there is no way of knowing, for sure, until the units have been pulled and bench tested.  This is expensive to have the shop do it because of the high price of labor these days; it may very well be cheaper to just replace one unit or the other.  If you know how to bench test the units by your self it would help.  BUT: if the problem is in the wiring harnesses somewhere, replacing the head or the amp may not solve the problem.  AND, you might even end up blowing a perfectly good unit!

So, be brave; pull the units out and bench test them yourself and see if they are good or not.  You can do it by running some long wires from the battery directly to the removed units power connections.  Hook up known good speakers directly to the power amp  (they can be test speakers, you don't have to remove the speakers from your car).

You may, to solve the problem, need to trace down all the wires and make sure they are not pinched and shorting to chassis ground or something like that.

Maybe this will get you started down the right path; then come back and let me know the deal further.

C.