After spending a ton of dough and endless hours of work getting the old girl ('92 LT1/A4 coupe) in good mechanical shape, the Bose system decides to crap out just as the driving season is about to get under way!

The system was working just fine all spring. Took the car on an errand today, listening to the stereo all the way to my destination. Parked, went in and took care of business, came back out, fired up the engine, turned on the stereo and all I get is whistling that changes pitch with engine RPMs. No sound at all. The head unit appears to be working just fine. It still displays my station and changes channels no problem. The antenna is going up and down no problem. CDs don't play. Cassettes don't play. Nothing. I checked the 10 amp radio fuse in the fuse panel just to be sure, and it looked good.

So I start flipping through the FSM and the troubleshooting chart hints that it might be the amplifier relay under the driver's dash. An hour and a half later, I'm looking up at the place where my amp relay SHOULD be, but it's not there. According to several diagrams in the FSM, there should be two relays in that location right next to each other, one for the amplifier, and one right next to it for the fuel pump. There's only one. There is an empty spot on the bracket for another relay to be hooked to it, but there's nothing there. The one that is there is in the position that the FSM says is my amp relay, so I ran out and picked up a replacement relay. No dice. Still no sound, just whistling. Dejected, I put everything back together and called it a day.

So, my initial thought is go just scrap the Bose stuff and go with a new receiver and four new speakers, but just on the off chance that I might be able to revive the Bose system, any thoughts or advice?

Sooner or later everyone that owns a Corvette with a Bose system in it faces what you are. Mine still works and I will keep it as long as it functions, but eventually I will replace with a new system. I know from other posts that the best thing to do if you do change out is to replace everything wires and all. Hopefully you can find it and fix it. Good luck on it.

Andy knows a ton about sound systems and will chip in soon I'm sure.

If you want to keep the Bose system, parts and rebuilds are available. I have a strong feeling Andy will say .......


I'll let him tell ya.

It actually sounds like the reciever module has died.

If you want to keep bose, that is serviceable.

Otherwise, repeat after me: gut and replace.

Thanks guys! I'm assuming the receiver module is the part that's buried deep inside the passenger side of the dash, huh?

Gut and replace, gut and replace, gut and replace...

yea, behind the glove box.

Thanks again guys. Since it's likely the receiver module, I'm really leaning toward a new system and speakers. There are a couple of good independent car audio businesses in my area, so I'll probably get in touch with them when time and money allow. I'll ask around and make sure the one I go with has done installs on a C4 before and knows the ins and outs.

Good luck with that.

Many shops will claim experience, but really don't have any.

The way you test them? Ask how they wire in an amp. Where do they get good ground? Some will say seat belt or seat brackets, but that really isn't a great ground.

The best ground is back to the battery - and I don't care what the amp maker says on the subject. So there!

The thing to doing audio in the Vette is taking the car apart correctly, and I suspect you already know how to do that.

Do me a favour and check out the Rockford-Fosgate POWER series amps. I like the lack of size, just curious about SQ.

So, a couple of things I've discovered:

First, I solved the mystery of the missing relay. In looking at the FSM a little closer, the fuel pump relay that was supposed to be next to the amp relay only applies if the car is a ZR1. For a standard coupe, it is correct for the right-most position on the relay bracket (to the right of the steering column) to be empty. This means that the relay that I replaced was in fact the amp relay.

Second, also upon closer inspection of the FSM, I see that there supposedly is a "secondary fuse block" adjacent to the receiver module in the right hand (passenger) instrument panel. I assume these fuses are hidden from view unless the lower trim panel is removed from the passenger side dash. I think I need to go after those fuses to see what condition they're in. Since I successfully removed and replaced the driver's side trim panel and knee bolster, the passenger side should be a piece of cake, right?

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Kudos for being able to find that in the FSM, it takes a bunch of searching to figure out that there's only the one relay.

Yep, the fuses are under the carpeted trim panel below the glove box. I had to pull that on my 92 to find the cigar lighter fuse so I could power my GPS.

There's also 5 other relays there including fuel pump.

IIRC, there's one of those nasty star nuts at the rear of that trim panel (the washer type nuts that go over a plastic stud).

Thanks Bill! Here's hoping that I find a blown fuse down there and get my tunes back online.

BTW, I really dig your signature line! That's great!

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Ha, I've hit the walls with both front and rear but never looked to see how far I pushed them.

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There is a radio control fuse there, labeled RDO.

Yeah, I'm pretty sure that's the one that protects the receiver module, a 10 amp I believe. I probably won't have the time to dig into it until early next week.

Fingers crossed...

Gurus, could you clear something up for me?

Per my post above, I still have yet to check the fuse under my passenger dash, but making the assumption that it is good, I'm looking at my options going forward.

I have found an online Corvette salvage dealer that has several CDM/receivers available for $195.00 plus a $50.00 refundable core. So that's one option.

I also stopped by my local car stereo dealership and priced out a completely new system (a Kenwood KDC-148, four new speakers, mounting hardware and labor to install everything including a complete rewire) and was handed a quote for $730.00. This really isn't an option, because right now, the money just isn't there.

So I started thinking about option 3; just replace my head unit with the aforementioned Kenwood, but use my existing Bose speakers as I presume that they are still good. Crutchfield sells the Kenwood unit for $79.00 with free shipping and including all the hardware that I would need except for this radio adapter http://www.crutchfield.com/p_12070185 ... tion-Adapter.html?tp=3486 which is another $49.00, but they claim I can save 50% when I order it with a receiver.

I'm really leaning now toward option 3 for several reasons. First it's the least expensive. Second, it gets me started with a new system, and sets me up for a time down the road when I can finish the job and replace the speakers. Third, this is something that I think I can do myself.

What I'm not understanding here though is, does the adapter actually bypass the entire CDM/receiver unit buried in my passenger dash, or does it still require some level of functionality of the receiver module in order to work (remember, we're going on the likelihood that my receiver module is bad)? In other words, will this work?

Again, I would LOVE to go whole hog and gut and replace everything, but like I said, right now I need to take the most economnical approach.

Thanks in advance!

Ron

We repair all CDM's for $175. Buying a used one is a crapshoot. Ours carry a TWO year warranty. We are the SE distributor for BOSE and sell amps that NEVER fail.

It does integrate with the control unit. The control unit is still used to distribute the signal to the speaker amps.

I did just what you are considering, but I used a new Pioneer DVD Nav System. I was pleasantly surprised when I first turned it on. It sounds awesome! Which many people probably call BS on, but it really does sounds great. Much better than the old Bose HU. I also bought the Crutchfield adapter harness but did not buy the HU from Crutchfield because I found it on Amazon cheaper.

The only problem I have experienced with this arrangement is that we will have the Pop on start up and pop on turning the system off. This is because the power for the speakers is already on when you turn the HU on and still on when you turn it off. I found a guy in California that owns an audio shop and he has the relay/filters to rid the pop, but they are like $25 each and you need one for each amp. Besides that, the pop will not hurt the speakers and if you can ignore it like I do, its not a problem.

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That means I still need to replace the receiver module regardless. Poop.

Depends on what went TU inside the module. The circuits for the speakers may be ok. Just a thought

I know that Andy will say to gut it and install a turnkey system and that is probably the best way to do it, but I was lazy and didn't want to start modding stuff to fit speakers and amps and wires and you know,.... all the stuff that goes with it.

Well, I took a leap of faith today. I actually called Crutchfield this afternoon and spoke with one of their support reps and gave them my whole story. It sounded as though he was familiar with the Bose systems. I told them about my concern whether the adapter harness still required the use of the receiver module. They guy told me that the harness completely bypasses the receiver module, so I'm holding him to his word. I went ahead and ordered a Kenwood KDC-348U receiver, and the GM Tuner/Amp Bypass Tuner/Amp Bypass harness. Everything was $155.00 delivered. All the hardware other than the harness was included for free, so I think I got a decent deal here and it definitely fits in my budget for now. I guess we'll see if the harness really does bypass the module altogether.

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Hey biggrizzly, would ground loop isolators help with the "pop" problem?

Per my previous post, all of my new equipment has arrived and I'm planning on doing my install this coming Saturday (I'll post up some notes when I'm done, and if something really relevant comes up, a pic or two). I was doing a bit of reading and discovered that some folks swear by ground loop isolators and some swear at them. I'm going to try my install without them and see what happens, but I'd be curious to hear if any other Gurus have had experiences with them, good or bad.

SUCCESS!! The old girl has tunes again!

It took me about nine hours start to finish, but the new Kenwood went in without too much drama and I have music to cruise with again! The Metra 70-1857 harness DOES completely bypass the entire CDM/receiver module in the passenger dash. Let me just say, that module is BURIED in there. It took me a while to figure out how the connections were made to the harness, but I got it figured out. There are five total plugs that plug into the receiver module, two on the driver's side of the module that presumably come from the head unit in the console, and three on the passenger side that are power connections, speaker connections, etc. I removed all five connectors from the module, and connected the three from the passenger side to the new harness (one blue, one white, and one black). I covered the two from the driver's side in electrical tape and tucked them up into the dash for safe keeping. I also had to remove the air vents in the passenger dashboard and use a very long screwdriver slid down into the dash from the vent opening to knock the antenna cable free of the receiver module, and worked my fingers up from underneath the dash to grab ahold of the antenna cable and pull enough of it down to reach the Metra harness. Just press the antenna connector into the female connector on the harness.

The other end of the harness goes to the new receiver in the console. The harness has three black ground wires that all get connected together along with the ground wire from the receiver's harness. There were also red, yellow and blue wires to be connected. I used a simple orange wire nut to connect the four ground wires together, but I used these that I bought from Crutchfield to connect everything else: http://www.crutchfield.com/p_669PP500 ... ml?search=posi+connectors. Pretty cool little design on these. They're a two part connector. You separate the two pieces, twist your wires together and insert them into the bottom piece, and then screw the top piece down on top of them. Everything gets clamped together nice and tight.

The Metra receiver mounting kit that comes from Crutchfield leaves a bit to be desired. Cheap, flimsy plastic, but in actuality, the plastic did kinda' come in handy when I was trying to get the new receiver into the console. The little "ears" that stick out when the receiver is mounted on the bracket give just enough to "snap" past the edges of the console surround. Getting the original head unit out was a son-of-a-gun. The ears are metal and I had to bend them a bit in order to get the old HU out. I also taped off and tucked away the wire connectors that formerly attached to the original head unit, as those are not used either.

Once I had the old HU out, I had to cut the very back panel out of the plastic housing that wrapped around the HU. This is required to afford enough room to route all the wires. I used a Dremel tool to do this, with a straight bit on it. This was a scary operation, because there are yellow wires going into a yellow junction box right in the same area, and these no doubt are related to the air bag circuit. Be careful with this. The Dremel makes a mess too, leaving tiny bits of black plastic all over the inside of the radio cavity. A good shop vac comes in handy here. Also, unfortunately, I had to mount the new reciever in the very bottom slot of the double-DIN opening from the old HU, as when I tried to mount it in the top slot, even with the plastic panel removed, the RCA cables pressed against a metal bar that ran behind the plastic housing. Fortunately, it only ran across the top-most slot, leaving enough clearance for the wires when mounted in the bottom slot. I fabricated a filler panel out of some bulk hobby sheet plastic and spray painted it semi-gloss black.

The only other grief that I had was trying to find a place to stuff all of the extra wire from the Metra harness. They give you more than enough to accomodate GM cars where the receiver module is a long way from the head unit, but on a '92 coupe, it's only a couple of feet, so there's a LOT left over. I stuffed mine up inside the lower trim panel under the passenger dash and did a lot of pushing and grunting to get that thing to where I could screw it back into place. Big fun. The whole installation looks nice and clean overall, so I'm pretty proud of myself. Never did anythinig like this before.

The sound quality is just okay. The stock Bose amp/speakers are definitely the weak link in this equation. It's good enough for my needs though and I'm happy with it. I'm also having no issues with pop, whine or buzz, and the antenna goes up when it's supposed to and goes back down just the same. It's also nice having USB and Aux connections too. Most of the buttons and controls on the Kenwood KDC-348U are REALLY small and a bit fiddly, but overall it's a nice piece.

Just in time too; the weather here in the Chicago area is FINALLY starting to become very summery!

Glad to hear it's up and running. Maybe new speakers down the road??? Where are the pics

Matthew

That deserves an Atta Boy! Way to jump in and get it done!

Yeah, I probably should have taken some time to take a few pics along the way, but I was so caught up in just trying to get it done in one day, and a bit nervous about screwing something up, that I just didn't bother with the camera.

Here's a pic of the finished product though...




I will add that some pics that I found online on the "other" forum really saved my rear end, as it showed me exactly how the connections from the receiver module connected up to the Metra 70-1857 harness: http://forums.corvetteforum.com/c4-te ... io-install-questions.html

And yes, new speakers will be forthcoming at some point, but right now, I'm just enjoying the music!

looks like a real clean install!!!

Just a quick update on my system. Discovered that my right rear Bose amp wasn't working. The previous owner must have given up on it as when I found I was getting no sound from that speaker, I pulled the cover off to find the amp connection unplugged. Plugged it back in and discovered that I got just some faint static. I found this guy on eBay: http://www.fixworks.com, and figured I'd give him a try. He rebuilt the amp and had it back to me in about a week. Plugged it in and it worked great!

I also replaced the rear Bose speakers with a a pair of 6.25" Sony X-Plodes that a good friend gave to me. They're 4 ohm, where the stock speakers are only 1 ohm or so, but they seem to work just fine. With all four speakers now working and a little tweaking with the EQ and fade, I got a pretty decent sounding system.