Hello All, Great forum here. I have a 97 Expy EB with the Mach Sound System and have discovered one of the rear doors speakers doesn't work. So off I go and "special order" the plain jane MACH door speaker. Now when I connect it, It STILL doesn't work. Ruled out "dud" speaker by testing on the other side, where it works fine. Upon further examination with a meter, I found that the wires for this speaker check differently than the working side. I had the stereo ON and connected my meter to Chassis ground. Probing the speaker connectors, I had 6 VDC +/- at both the positive and negative tabs on the WORKING side. However on the Broken side, the positive terminal had ~6VDC, BUT the negative terminal had 12 VDC..... OK, so something is amiss upstream from the door speaker. (likely explaining why this speaker burned out)
I have looked at wiring color charts, but have not been able to find a full diagram. Oddly my speaker wires (in the doors) correspond to the colors listed for a 98 Expy! Is it possible that they change color somewhere between the head unit and the speaker?
I have read somewhere that the door speakers get their signal from the AMP, not the head unit. Could this explain the color difference I am seeing in the wires?
Do these symptoms sound like an AMP problem, and where all do the speaker signals travel. I do have good sound from all other speakers and the rear subwoofer...
I now have virtually the entire interior disassembled with the exception of the subwoofer area. By the way, the CD Changer is removed due to a battery drain and the Rear Integrated Control Panel is also disconnected due to a battey drain. I have connected both of these and it doesn't affect the speaker wire voltage issue unless the drain issue is the cause???
Please help, Any and all thoughts might get me on the right track. Thanks!

 

In my opinion, I would say it's a bad amp or headunit. If you got a new speaker and it works on one side but not the other, then the signal is not getting to it. I would guess the amp, I've seen more of those go than actual headunits. The amp is also the reason for the wire color change most likely. If you can figure out the inputs from the headunit and hook them up to the speaker so that you essentially bypass the amp, that will rule out the amp.

 

Thanks, I plan to further disassemble it tomorrow. Is the Amp I am looking for the one on the subwoofer box, or is there a different one for the door speakers? I am getting the weird voltages at the bad speaker location, I want to trace them back to the origin, either Amplifier, or Head Unit to see if that is the problem.

 

the amp should be behind the pass. side pannel in the rear it's kinda a pain to get to but that's it.

 

Update: I have removed the subwoofer enclosure w/ AMP and there are NOT any door speaker wires at that location. Simply two heavy wires on a power connector, the amp trigger and tiny signal wires on the other connector into the amp. Output is only the two wires to the subwoofer. I am now going to look at the back of the head unit to see if the problem is originating there. Does anyone know if there is ANOTHER AMP in this???

 

I dont know **** about expys but i have done a few systems in other cars with factory amps and they are usually under the seats

 

I believe you need to check those voltages in VAC. It might give you slightly different readings. IT also bears out that it should not be directional, it flows from one point and returns to a point near that.

I would also test the signal going to the amp, it could be in the radio or the amp.

 

The amp for your door speakers is under the climate controls in your dash. You'll need to remove the radio, climate controls and floor duct assembly to remove it.

 

Thanks all, I am taking a break from this mess until maybe this evening. Three speakers and a sub still sound pretty good. I plan to pick up with the head unit and Yes, I did see a glimpse of the Amp behind the heater controls. Does the console have to come out to remove the amp? I am going to get some harness adapters for bypassing the amp and my son has an extra Sony head unit that I plan to use for testing. Does anyone know the pinouts for the signals from the head unit. (On the black double row connector, it appears to be the one going to the amp)