Recently the music in my car has been going dim, and then returning to normal. I believe that I have a faulty amp. As of now, i'll be driving at some points and the music will be normal, clear sound etc., and then the music will just go dim until i hit a bump in the road when it restores to its normal sound level. Again, this is very frustrating, and i'm looking to replace the amp. How can i test the amp to see if its in proper condition. I dont have any type of special electrical tools etc. Any suggestions would be appreciated. TIA

Agron
1989 300E (107k miles)

I don't know about the specific amp in your car, but I have experience diagnosing home stereo equipment. What you describe is difficult to analyze, because it is not constant. Some things to note, that will help diagnose: when the sound fades, is it all of a sudden, or a gradual fade? You describe a bump as suddenly bringing the levels back up - does it always come back at once, or is this also ever gradual? Does the loss of sound occur more frequently when the stereo has been on for awhile, or does it also happen when it's first turned on? Does the sound fade from all directions (left right front rear)? And finally, does the source (AM/FM/other) seem to make a difference in the fading?

Chances are it's a loose connection on the circuit board, most likely the output stage of the amp; this is just a guess. If your car has a separate amp, it may be wire problems going into the amp; or possibly speaker wire problems. The answers to the earlier questions would help sort this out.

1st thing, I'd check the RCA connections b/w the Head Unit and Amp. If fine and problem continues, can you fade your system and monitor just the front or back channels? Being able to further eliminate one set of channels or another will help you narrow things down...from there, if it's only one set I'd swap the front & rear outputs & see where it leads you. Might help determine if it's the HU or the amp that's problematic.

What makes you think it's the amp and NOT the HU? Just curious...good luck!

alanwolf:

When it first started to happen about 2 months ago it wasnt constant, but now it happens all the time. The amp that is in discussion is a 690watt 4 channel "select by qupix" (POS). About the sound it is not gradual, but all of a sudden the sound will go away until i hit some type of bump in the road or something to that extent. I've noticed that when the sound goes dims, and i play with the the sub-enclosure the sound will come back (pushing it from side to side). This amp is attached on the back of a sub-enclosure. This happens at all times whether the radio is just turned on, or its been running for an our. I just dont know whethere the amp is shot, or theres some sort of play in the wiring. Is my best bet to take it to a professional and have it checked out. Also, like Mike said i'm going to check out the RCA cable between the head unit and amp. Im just annoyed that when i'm driving all of the sudden the sound dims until the music is distored, and then you have to wait until you hit some type of bump in the road in order for the music to restore to normal. again thanks alot.


Agron
1989 300E (107k miles)

Can you rotate the sub enclosure so that the leads (input and speakers) are accessible? If so, do , and then when the sound goes out, rather than rocking the entire enclosure, gently jiggle the wires, one at a time. If you get the sound to come back with a certain wire, that will be your problem connector. This really sounds like a loose connection. Especially with the amp mounted on the sub enclosure, where it is subject to a lot of vibrations.

It's a good idea to unplug each connection, again one at a time so that everything is hooked back up properly, and replug it. This will both give you a sense of how firm the connections are and will also clean them slightly, so that they make better contact. You may be able to escape a trip to the repair shop–good luck.

Alan

Well, I've had all I can take and today i stood in the driveway under the bright sun, and disconnected all the wires and cables from the amps and sub-enclosure. I tried to see if there was play, but nothing came to work my way. The car is sitting in the garage, without anything connected, and its on its way to the shop tomorrow. When it comes to electrical diagnosis--Im just lost....I will keep you guys updated and inform you of what was the culprit. Again, thank you Alan and Michael for your input. Much much appreciated......


Agron
1989 300E (107k miles)

I took the car in today to my local "stereo guy" and I wanted to kick myself when he told me what the culprit was--a lousy fuse. He changed the fuse and viola, I was bopping my head back and forth again enjoying some fine tunes. Took about .03 seconds to change.


Agron
1989 300E (107k miles)