2003 Amp replacement, bypass

[21 Racing]

I had a bad amp, typical problem with corrosion. I had made a bypass with my old amp to verify that it was bad and got the display to come up and some sound however there was a lot of static.

Purchased a supposedly good used replacement amp and installed it. System was dead, opened the new amp and had corrosion also. Put my bypass back in and still dead. Checked fuses and they looked good. Checked the fiber optic buss by removing the amp, head unit, CD player, and radio and shinning a light through them. All checked good.

Checked power to each unit and was good.

Is there a reset or something that may need to be done if there is another amp that is installed?

[9-3 Aero]

The WIS replacement procedure does not call for something like a reset.

However, looking at two Tech2 fault tracing procedures pertaining to audio system / O-bus, are preliminary steps to be taken, momentarily disconnection of power. With regard to one procedure, "ICM display off, radio does not work", is the step to pull fuse #14 (ignition "OFF") for one minute to provide O-bus being "at sleep", and then fit the fuse again and turn ignition "ON". The other procedure, which I now do not find, was to disconnect battery for one minute (or four - if rear amplifier is installed).

Maybe there's nothing to loose by trying?

[21 Racing]

Tried that and did not fix.
I did notice that when it was working the display was showing "no onstar". Not sure if that is because of no subscription or something else.

[9-3 Aero]

Hmm, given you have the telecommunication unit ("onstar module") as well, when checking the O-bus for light, did you disconnect the fiber I/P for verifying light to that unit as well? The unit is powered by fuse #19 in the rear electrical center. Whatever the configuration of the audio in question is, is this unit right next the Infotainment Control Module on the fiber loop. The following units would be DVD, 6 CD and rear amplifier before front amplifier (AMP1). Light to be verified on I/P here as well (I do note you have checked ).

[21 Racing]

Yes, I have checked on the fiber loop. It does have light going into the units.

I am about ready to pull everything out and install an after market sound system.

[9-3 Aero]

As I understand it, did the system (O-bus loop) die, meaning no side indicators "tick-tock", audio etc., when working on the front amplifier (AMP1). Assuming all fuses and optical lights are good, as you've checked, would a contact problem with the O-bus on the I/P / O/P of AMP1 be one likely cause of the problem. Was / is the way you made the bypass of it something like the Etadyne MOST Loopback Connector: SAAB Products, or what?

[21 Racing]

I made my own loopback connector using the fiber optic cables from the bad amp. I did pull the radio control and open it and did verify that it is transmitting an optical signal but not receiving a signal. I need to follow the transmit signal through to see where it is getting lost. I do know that it is getting to the amp 1. Where does it go from there?

[9-3 Aero]

The Entertainment Head Unit (EHU), including the radio receiver, is the unit next to the AMP1 on the O-bus loop:


The Infotainment Control Module (ICM) is the "bus master". It's encouraging if that is the module of which you verified light on the O/P. Then I would (re-)check the I/P of the EHU.

EDIT: No swapping of receive -/transmit terminals through checking for light is assured?

[21 Racing]

I did find that diagram and did some more trouble shooting last night.

Found that the signal was getting to the EHU but not coming out. Therefor the EHU is bad you would think but I had my suspicions. One thing I did not like is that the optical signal coming into the EHU did not seem as bright as the one going into the other units. Removed my bypass for the AMP1 and cleaned it up and made sure there was a good optical connection there. Put it back together and worked!

Lesson learned is that even though there is a signal there if it is not bright enough then the unit that the signal is going into may not detect it.