Bose Symphony No Sound: Started Troubleshooting

[gilber33]

I drove the car to work on Monday with a fully working stereo. Got in it at lunch and had zero sound from speakers. No, it wasn't muted. I turned the stereo on and off and did the full reset by pressing the AM/FM & Setup buttons together and that did nothing.

As I started looking into it it appears the Bose amp runs all speakers and that is the place to start. Before this I would get a real small hiss sound coming from the speakers even when the car was off since the radio system is always "on" and that noise was completely gone, leading me to believe it is the amp.

I picked up a used amp from a gentleman to test out and that did not work. Granted, when he gave it to me he noted that it worked, but in the summer on hot days it would cut out. I also know the amp hasn't been used in a while since it came out of his car he was parting out. So I started troubleshooting on mine.

I used this wiring diagram of the harness since it's the only one I could find. The source of the pic is from a b5, so I don't know if the amp would be different or not.



Based on this I tested the power supply:



That was good. Then I tested the switched 12v. Based on the diagram, the switched 12v is pin 6. I read 12v with the radio on and with the radio off. Not sure what that means.

Next I checked the resistance at the ground. The first picture is a test pic where I tested the resistance from the tail light mounting bolt to a ground in the rear just to get a base number and make sure it was working. The second pic is the same ground in the trunk and the ground on the bose amp wiring harness. The resistance is higher, but I am not sure if that is partly because the current is traveling quite a bit further to test the resistance.





So I am not sure where to go from here. I see three possibilities:

1. The amp I got is bad and not working either.
2. My amp is fine and the ground is bad.
3. My amp is fine and something with the switched 12v source is up.

Hopefully someone can point me in the right direction. Any help is appreciated.

[diagnosticator]

Check for voltage at the low level audio outputs from the head unit to the amp.

[gilber33]

Which pins would those be? 19, 20, 21, & 22.

[diagnosticator]

Yes correct. Is your Bose amp 25 pin or 32 pin? Check for AC voltage between + and - for each channel line level outputs. That would be between terminal 7 - and 19 20 21 and 22 +, Line level inputs from radio to amp. check with the amp connector disconnected.
Multi-pin connector, 32-pin

1 -
Terminal 30
2 -
Terminal 31
3 -
Bass Loudspeaker R100 (+)
4 -
Loudspeaker, left rear (-)
5 -
Loudspeaker, right rear (+)
6 -
Positive switched from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
7 -
Signal ground from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
13 -
Inside Loudspeaker R70 (-)
14 -
Inside Loudspeaker R70 (+)
15 -
Bass Loudspeaker R100 (-)
16 -
Loudspeaker, left rear (+)
17 -
Loudspeaker, right rear (-)
19 -
Left front signal from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
20 -
Right front signal from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
21 -
Left rear signal from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
22 -
Right rear signal from Radio R / Navigation System with CD Drive Control Module J401 / Radio/Navigation Display Control Module J503
26 -
Loudspeaker, right rear (-)
27 -
Loudspeaker, right rear (+)
29 -
Microphone input (+) from Inside Microphone R74
30 -
Microphone input (-) from Inside Microphone R74 (-)
31 -
Loudspeaker, left rear (+)
32 -
Loudspeaker, left rear (-)

Copyright © 2008 Audi of America, Inc. and Bentley Publishers. All rights reserved. Last processed:

[gilber33]

32 pin.

Pins 19, 20, 21, 22 all read 3.9v with the radio on. With the radio off the multimeter was showing -.3v.

Reread your post. Those readings were grounded to the body, I will use the harnesses ground. If I'm reading it correctly the negative prong from the multimeter will go into pin 7 and then check voltage at 19, 20, 21, and 22.

[diagnosticator]

32 pin.

Pins 19, 20, 21, 22 all read 3.9v with the radio on. With the radio off the multimeter was showing -.3v.

Reread your post. Those readings were grounded to the body, I will use the harnesses ground. If I'm reading it correctly the negative prong from the multimeter will go into pin 7 and then check voltage at 19, 20, 21, and 22.

That is right, negative meter probe to 7 and positive to 19 20 21 and 22 use AC meter voltage with harness connector disconnected from amp. The measured audio line voltage should vary with the audio program, on each channel.

[gilber33]

That is right, negative meter probe to 7 and positive to 19 20 21 and 22 use AC meter voltage with harness connector disconnected from amp. The measured audio line voltage should vary with the audio program, on each channel.

Got it. I'll try that. I haven't used AC to check voltage before. Should I be using Vac 200 or 600?

Thanks for your help so far.

Sent from my SM-G920P using Audizine mobile app

[diagnosticator]

Got it. I'll try that. I haven't used AC to check voltage before. Should I be using Vac 200 or 600?

Thanks for your help so far.

Sent from my SM-G920P using Audizine mobile app

Use the lowest voltage setting or let the meter autorange.

[gilber33]

Use the lowest voltage setting or let the meter autorange.

With the multimeter on Vac 200 and the negative probe in pin 7, pins 19 - 22 would read .1 to .3 and then drop to 0. If I set it to 600, I got nothing.

Sent from my SM-G920P using Audizine mobile app

[diagnosticator]

With the multimeter on Vac 200 and the negative probe in pin 7, pins 19 - 22 would read .1 to .3 and then drop to 0. If I set it to 600, I got nothing.

Sent from my SM-G920P using Audizine mobile app

Yeah, if a lower voltage scale is not selectable, then the resolution of the measured voltage will be compromised, since the voltage level of the line level outputs is less than 20 VAC. Also, the fact that the measured voltage drops to zero is consistent with no audio sound output from the amp. I suspect there is a fault in the radio head unit. This is a good time to upgrade to a Sym II+ radio. A Symphony II+ has a lot better sound output. You only need a harness adapter wired for Bose to connect the mini ISO connectors to the quadlock connector used with the Sym II+. Sym II+ radios are available a very affordable prices. Make sure you get the security code with the radio. You will also need a set of 4 release keys to remove the radio from the dash.

[gilber33]

Car came with an RNS-E head unit, so that's really sucky if that's the culprit. I also checked voltage at the same pins using the 9v selection on the multimeter and grounding it to the car and they all did the same thing. Started anywhere between 2.5v to 3v and quickly dropped. I have an old school multimeter I'm going to try quick.

Sent from my SM-G920P using Audizine mobile app

[diagnosticator]

A replacement RNS-E will cost more, but given the diagnostic voltage measurements, I am practically certain the HU is the problem. Electronic devices randomly fail due to their nature routinely.

[gilber33]

Well, I'm not exactly sure what happened, but when I put everything back together last night, the speakers worked again. I do not know if that means that the head unit is going out or something else was going on. I took a video of the meter when I tested the speaker output pins from the radio and theyou were goofy. I'll post that later.

I guess we'll see how long the speakers keep working.

[diagnosticator]

That is good news. Something must not have been connected fully.

[gilber33]

I have no idea. I had removed and reinstalled the amp a few times to me sure it was seated correctly. Hopefully it keeps working and something isn't on its way out.