Bose Amp Repair Project

by Bryan A. Thompson

Last Updated 11/25/2001

 

Thanks to Jeff Travasos for the donation of two amps to the Bose Amp Repair Free Information Project.
 

Note:  This is just a working draft, and is by no means complete.  If I can locate a schematic for these amps, or reverse-engineer a partial one, it'll be much easier to troubleshoot problems.  My first impression is:  

Why?  Because it sounds really good?  No, that can't be it.  To save money?  Not in the long run.  Because you want to keep it stock?  Okay, maybe. What breaks on these?  Everything.  The amps self-destruct and the speakers fade and die in the sun.   

Think about this.  These critters are really complicated.  The circuitry is a *lot* smaller than the cluster.  Do you *really* want to do this, when you can send the entire enclosure to Bose and get it completely rebuilt for $75?  That's a great price.  If your amp is old enough to be shot, the speaker probably is, too, and there's no chance of fixing that one yourself.

If the answer is yes, think about what you'll be left with when it works again.  A crappy 50W one channel amplifier connected to a 4" speaker in a box that takes up waaay too much space.  6x9's fit in this space perfectly.  I have a set of 6" 2-way components in mine and couldn't be happier.  You'll need to buy an amp that'll run them, but small 100W amps (50Wx2) that interface with the Bose wiring and that fit neatly under the storage compartment or front seat or even in the enclosure of one of the rear speakers cost about $50. 

Still want to fix your Bose amp?  Take it out of the enclosure and smell it.  Burned semiconductor junction has a smell like no other.  If your amp smells burned, don't bother - you can't get all the ICs that you need to fix this problem.

Next look at the back of the board.  If the enclosure leaked water and corroded the copper on the back of the board, don't bother trying to fix it.  Instead save it for parts or better yet, mail it to me to include in the project.  

Next look at the electrolytic capacitors.  They're the ones that look like a small aluminum can with a green or blue plastic overwrap.  See any residue (other than the hot-melt glue all over these things) at the base of these?  If so, replace 'em.  You can find parts at Digi-Key.  Chances are that whatever killed these also killed your driver FETs, but who knows, maybe you're one of the lucky ones.  Plug it in and try it.  If it's still not working, proceed to the next step:

 

Look at all those little flattened yellow cylinders at the IC end of the board (C151,C162,C163,C141,C140,C131,C122,Z121,C121).  They're cheap-ass polypropylene capacitors.  Replace them all with components you find at Digi-Key.  Use 50V versions of each.  This simple repair solves the most common problems with these amps - most of the cracking, popping, hissing noises are due to these things leaking (shorting internally).  If you had a Digital MultiMeter you could remove them and check to see which had the problem, but if one's bad the others probably aren't long for this world.  Digi-Key gives great quantity discounts, so you might as well order enough to do all 4 amps.

While the amp is out, you might think about resoldering all the high-current connections on the back of the board.  These corrode over time and cause problems of their own that can be very similar in nature to the capacitor problem, so while you're soldering away, have a go at these.  Resolder the two inductors and transformer (yellow things with red wire around them), all four FETs (the two three-legged components on either side of the inductors), all 6 wire connections to the outside world, and anything along the larger copper traces on the back side of the board.

Here's some info from readers:

Brian - I did find out the # for the
power fets they are irf z44n or ir 902 .

Thanks
johnwiencko@hotmail.com

From Bob Golden:

Bose Radio Compliant—The speakers cut off and on at times.   This may require amplifier repairs or replacement.  However before you spend all you dollars for amplifiers try cleaning the tone controls.  The Bose audio is a unique audio system.  It requires total control over any pre-amp parameter.  If the tone controls are scratchy, chances are they are causing the channels to drop out.  Use a cleaner that contain a lubricant and spray a small amount in each control.  Work them up and down a few times to clean the oxidation off.  Again make sure you use a cleaner with a lubricant.  If the controls are void of lubricant they will become very difficult to operate.

 

Below is a thread I captured off the CorvetteForum:

I assume the LOUD occassional buzzing means the amp on my front Bose in my 91 is shot. I suppose it is behind
the speaker and is accessible. does Chevy still sell these and how much are they? Is their an alternative to buying
from the dealer? 

[This message has been edited by bulldogbill (edited 08-22-2000).]

IP: Logged
keilo
Senior Member 

Posts: 185
From:E. Stroudsburg, PA
Registered: Feb 2000 
posted 08-22-2000 09:53 PM 

it's about 200 bones for them, I replaced my head unit with a sony md-60. it cured the popping and buzzing. But
the amps might help

------------------
Kei 
89 Red Ragtop. K&N Filter, Stainless Steel Muffler elimilators, 160 deg thermostat, Cool Fan switch.

E.Stroudsburg, PA

IP: Logged
bulldogbill
Member 

Posts: 10
From:marietta, ga, usa
Registered: Aug 2000 
posted 08-22-2000 10:12 PM 

C'mon! $200? Is that right???? 

IP: Logged
Tom73
Senior Member 

Posts: 103
From:Austin TX area; (lost
1800 post in the great forum
melt-down and April 1999
registeration date.)
Registered: Aug 2000 
posted 08-22-2000 11:59 PM 

Belive that Chevy only sells the entire box, amp/speaker/enclosure. But Mid-America sells the amp for $90-$100
range. Can also check with some of the Vette Salvage dealers.

tom...

IP: Logged
vettenuts
Senior Member 

Posts: 3485
From:Wakefield, RI
Registered: Mar 99 
posted 08-23-2000 09:25 AM 

Just went throught this on my back one. Corvette Central had the best deal. Whole speaker assembly, 2 for $199.
I replaced both. In 93, the amp design was changed. The GM price for the new amp design doubled the price. Make
sure you get the new design, not the old one. The old ones are susceptible to heat related failure over time. The
ones I just installed are the new design. The other option, I contacted Bose and they will rebuild the unit (back
one) for $75 which is pretty cost competitive. You may want to contact them directly.

------------------
Bob T - 90 Roadster
Wakefield, RI
[VETNTS]
Member - National Corvette Museum
Member - Corvette Club of Rhode Island
Web Page www.corvetteforum.net/c4/vettenuts/ 


IP: Logged
Johnny
Senior Member 

Posts: 74
From:From Auckland, NZ, but
now NJ, USA.
Registered: Mar 99 
posted 08-23-2000 10:11 AM 

I replaced the front right on my 90, $178 from corvette central.

I think you have to replace the whole unit amp and speaker. Anyway that's what I did and it fixed the squealing
and popping.

1/2 hour job even for the mechanically challenged like myself.

IP: Logged
Red 90 L98 Coupe
Member 

Posts: 1
From:Sydney, Australia
Registered: Aug 2000 
posted 08-27-2000 07:27 AM 

Corvette Central has rear speaker amps for the 91 for $89 each. They also sell a "speaker upgrade" for $139 each
which replaces the standard (50 watt?) amps with 100 watt amps.

Whether or not you need to change the amp, speaker, or whole assembly depends on the problem. I have the
same problem and have just ordered a new amp.

IP: Logged
AFVETTE
Senior Member 

Posts: 326
From:Shiloh, Il 62221
Registered: Sep 1999 
posted 08-27-2000 08:48 AM 

Contact Bose, I believe they offer a rebuild service and it's less than $100 per unit.

------------------
Two Man "Submarine Fighter" Co-Pilot Lt. Cmdr, USS Corvetteforum SSB Y2K Blue
Vanity Plate:AFVETTE
USAF Ret
96 Polo Green Roadster
Shiloh, Illinois
Member Looking Glass Corvette Club

IP: Logged
Canned Ham
Senior Member 

Posts: 21
From:Huntsville, Al USA
Registered: Nov 1999 
posted 08-27-2000 10:27 AM 

This is a common problem on Bose amps produced by a from 89-91 in Vettes, Nissans, and and any other car
manufacturers that used the Bose system. Over a year ago there were many posts on this subject. If I understand
correctly all of the green capacitors on the amps were very low quality and heat causes them to leak(go bad) too
soon. It is extremely simple to replace the caps if you can solder or know someone who can. All you need to do if
you dont have alot of experience with electronics is to take the small green caps off and record their values and
find an electronics supply store and replace with same values but use 105 degree celcius temperature rating. All 4
of my amps went bad(sqeeling, popping,...) and the total cost to repair all of them was about fifteen dollars and a
small amount of time and they all work great. Hope this helps 

IP: Logged
corvetteman3
Senior Member 

Posts: 24
From:Baton Rouge, LA
Registered: Aug 2000 
posted 08-27-2000 11:54 AM 

Canned: What a great tip. That is what this forum is all about. Someone out there always knows the answer. 

------------------
77 White Coupe
89 Grey Coupe
90 Red Conv.

 

If you found something useful here, please consider making a donation to help keep this information free. 

Unless otherwise specified, the text and images in this page are the copyrighted property of Bryan A. Thompson, 1996-2006.  All Rights Reserved.