99 EB Subwoofer Has Low Volume

[Johnbugs]

Recently the subwoofer on my 99EB (95K miles) lost volume, i.e., at half bass setttings I used to hear a decent amount of sound from it, but now I have to max the bass setting just to barely hear it. I replaced the entire subwoofer assembly with a new stock unit thinking it may have been the amplifier or driver. I was able to do this replacement easily with the help of all my Explorer friends on this web site (thanks!). Fortunately, I have a second 99 XLT with the same Mach audiophile system that works. I swapped out the head unit from my EB to the XLT and the XLT sub worked fine. The XLT head unit in the EB gave the same low volume problem. I plugged and replugged connections at the amp and the back of the radio, problem still there. I checked fuses and all were fine. I still get a signal to the sub, but the volume is very low. Any ideas? I am grateful for any help here.

 

[scucci]

The mach system uses differential amplifiers for noise reduction. They have a + input and a - input plus a shield ground. If either the + or the - wire breaks you will get low sound level. Check the harness, especially at the connectors.

 

[Johnbugs]

Thanks for the quick reply, it is most appreciated! I have checked at the connections at the rear fo the radio, I will check again and then trace the wiring through the harness back to the subwoofer. Visual inspection presented no loose wires and a firm "click" when sliding the connector in the rear of the head unit and the subwoofer amp. Where might the ground be located?

Thanks again for your help.

 

[scucci]

The shield wire is wrapped around the the plus and minus input wires and grounded at the head unit end. See the attached Mach system schematic pdf:

http://www.explorerforum.com/forums/attachment.php?attachmentid=40347&d=1179974291

 

[Johnbugs]

Thank you for the diagram, it is most helpful. What is "High Audio Mute"? Now for the odd part, the subwoofer volume returned to "normal" today. This is after several days of use... I have no idea why it is working but it is. Thank you so VERY much for your help and providing me a better understanding of how this system works.

 

[scucci]

high audio mute is really like "remote turn on". The factory head unit has a mute button and that can turn off the sub woofer by removing the 5 volt turn on from the high audio mute terminal. You may have a poor connection somewhere that has been disturbed and now is a good connection, or perhaps a poor solder joint in the sub woofer system. Or it is possessed.