86-89 BOSE Head Unit and Speaker Rebuild Guide with AUX Input
 

All,

I spent a lot of time gathering information about rebuilding the 86-89 Bose stereo and speakers from the forums and across the Internet, including getting my hands on a set of factory schematics which allowed me to add an AUX input to the system. In order to preserve the information and help others, I compiled an extensive document on the procedures including:

• Why the Capacitors fail
• Replacing the speaker capacitors
• Replacing every capacitor in the Head unit
• Refurbishing and cleaning the cassette deck
• Adding an AUX input to the radio
• Parts lists for cassette belts and LED lighting for the head unit

The doc is attached as a PDF to this post and is 55 pages or so long. I tried to document each step with pictures to make it easier to follow along.

Have at it and feel free to PM me with suggestions or additional information you have that might be useful to include.

NOTE: Although I have the factory schematics, all of the diagrams within the document are original to me so there should be no copyright issues with this doc.

-SLVRSHRK

Excellent work! :thumbs: :cheers:

Excellent!!!
Found a problem though, sorry
Bose radio models 16125781 and 16041551 came in the 85 through 89 vettes not just 86-89

This is F A N T A S T I C - !! Obviously a labor of love - thank you for putting this all together. I have three of my four speaker/amp boxes out so I can begin rebuilding them.

Awesome, I have been searching for a while to find this information. I'd rather do the repairs myself versus sending my radio out.

This thread should also be posted in the C4 Tech section to make the information easy to find for those who may not think (or know) to look here.

Thanks for taking the time to but together such an awesome write up...it's obvious that this took a LOT of effort to compile, organize, and publish. You did a fantastic job with this write up!!

:cheers:

Great info. I need to repair the cassette play on my Bose radio from my 85. Your instructions say for 1986-1989. I thought the 1984-1989 Bose radios were all the same. Part # is the same as well.

Read post 3 above. Cruisinfanatic pointed out the head units were the same 1985-89. 1984 Bose head unit tape decks were the only ones different, so the instructions posted by SLVRSHRK will work for you on your 85. :thumbs:

Great work, will help a lot of people who want to repair the system. :thumbs:

First of all, thanks for all the work you put into this guide. It's been very helpful in refurbishing my 1985 Bose head unit. I'm a firm believer that sticking with the stock head unit is often the best option. They tend to look better and the speakers and amps are designed specifically for the vehicle, usually leading to better sound quality compared to aftermarket options.

Of course, a big downside to factory-original head units is that they rarely offer modern compatibility options. I'm planning on adding the aux input to my head unit, but there's something in the instructions that I'm not clear on. On page 38, you refer a "specific type of auxiliary jack designed for this very purpose". What makes this type of jack different from a standard one, do I have to order it from a specific place, or is it something that's more generally available?

There really are two kinds of headphone/aux jacks; those that simply connect your wires to the jack when it is plugged in, and those that will pass a signal when there is no headphone or other device plugged into the jack. This second kind is what you want because what we are doing is hijacking the signal path from the tuner and using it for whatever we plug into the jack. But when nothing is plugged into that jack, we want the tuner signal to pass on through.

In effect, when you add the jack as described, the signal from the tuner takes a round trip through the aux jack on it's way to the amplifier section.

When you plug the plug into the aux jack, you are disconnecting the tuner, and connecting the plug signal.

Make sense?

Here's an example of the type of jack the is needed: (I have no affiliation with this seller, just using an example)
https://www.mouser.com/ProductDetail...61NTBatA%3D%3D

and the datasheet:
https://www.mouser.com/datasheet/2/3..._cd-478709.pdf

Take a look at the datasheet. The lower left area contains the schematics. If you look at the schematic for this switch (35RAPC4BV4) you see it has five connectors. When nothing is plugged in, pins 3&4 and 5&2 are connected. This allows your tuner signal to get back to the radio. When you plug in a device, the inputs (pins 5 and 3) are disconnected and the terminals on the plug are connected to pins 4 & 2. This takes the signal from your device and feeds it into the amp section of your radio.

You need to be mindful and connect the correct pins to the correct wires. Be sure the wires from the tuner board connect to the terminals on the jack that are disconnected and the wires back to the amp board are connected to the terminals on the jack that contact the heaphone plug when it is inserted.

Hope this helps.
:cheers:

Gotcha, I think I've got the aux mod figured out at this point.

Regarding the cassette unit, the pinch roller hubs ("wheels") in my unit have all but disintegrated, but the rubber ("tire") is still intact. Luckily I have access to a 3D printer and am going to try modeling and printing new hubs for the rollers. If I'm successful and anyone is interested I can upload and share those models.

That's a great idea, and good luck. Please take lots of pics and document, document, document! I also have a 3-d printer and have found it immensely useful in making some hard to find parts. When you have a working design, please post it to Thingiverse.

If you have some more detailed photos of the pinch rollers than the ones in the document could you post those? That may be a good reference point for me as mine are totally unrecognizable.

https://cimg4.ibsrv.net/gimg/www.cor...f75e127610.jpg

This is probably the best I have. I don't remember if it made it into the doc.

PM me an e-mail address if you want the high res version for taking measurements.

Good Luck!

Thanks much SLVRSHRK for the very well documented write-up. I used it to repair two amps and refurbish my head unit. For a little while I only had one speaker working in my '88. One ended up have a bad speaker itself so I replace that. The other two I replaced all the caps and one worked right away, but the other one I found a bad chip capacitor on the lead side of the board. I ended up searching the web for what A5 meant on the surface of the chip cap, and found out that it was a .1 microfarad. Unfortunately, I ended up tearing the trace on one side of the chip cap on the very fragile 30 plus year old board. I had to repair it using a couple strands of copper wire and it wasn't fun soldering the chip cap to that side, but in the end it worked.

I replaced all but two of the caps in the head unit. The only two I didn't replace were on the board on the cassette unit that had the two small yellow wires soldered to the solenoid. I didn't want to take a chance desoldering the wires from the posts with the plastic surrounding them. No biggy I guess since it was just for preventative maintenance anyway. Thanks much again SLVRSHRK, your write-up helped my big time !!

David

Glad it helped save your units! Yes, the two capacitors on the cassette boards are by far the toughest ones to replace of all of them :)

SLVRSHRK, is it possible for the 86 Bose radio to have one channel not have output? I've got voltage to the amp, wiring tests good (continuity from radio to amp) the speaker tests good (swapped drivers door for passenger) , just no sound. All 3 other speakers and amps play great. I haven't been able to swap the passenger amp to the driver side, but I ran out of time this evening. I'll try to get them swapped to check. otherwise I'll be ordering parts and rebuilding the radio. Thank you for the repair guide!

If you'd like your radio tested, I'd be glad to do it free. Would just cost you shipping each way

Thank you Cruisinfanatic I just got another door amp hooked up and it's working.