89 bose radio problem

[vettedoc]

the bose radio in my 1989 conv. has a noticable alternator whine (for those non radio buffs- a high pitched noise that varies with the revs of the engine). Anyone out there know of a fix or filter that can solve this problem?

:Twist :dance

 

[Radar]

I would check for a lose ground wire someplace.

Radar

 

[Eagle85C4]

Remember the old condensers used in the old type points distributor? Well you can take one, mount it on the alternator and take the wire and connect it to the terminal with the large red wire. This allows the condenser to act as a filter and should filter the noise to ground. Remove the battery cable before you install the condensor.
Radio Shack sells a ground loop isolator that is equally adept at removing the noise, you place it between the ground and hot wires to the radio.
Do you use resistor plugs and wires? That will remove a lot of the noise as well...

 

[SPANISHVETTS]

I had the same problem when my alternator was going bad. One of the diodes had shorted letting 5 volts of AC flow through the electrical system.

 

[vettedoc]

Well I finally got to the bottom of the problem. I removed the two rear speakers and no more whine. I sent the amps to Dr. Don's and he turned them around in 24 hours and I reinstalled them today. It's really nice to listen to the radio without that horrible noise. Thanks for all the help guys. Happy crusin!

 

[Radar]

Just wondering what Dotor Don's charged for those repairs? I have one front and one rear amp out on my Bose system too.

Nice 89 you have!

Regards,
Radar

 

[Eagle85C4]

I can save you a few bucks....you pay parts and shipping...labor free to CAC members...

 

[vettedoc]

Radar-

I say go with the Eagle. You can't beat that offer.

Doc

 

[Eagle85C4]

For those interested....

The amps have an inherent problem with its filter caps. They are the two blue thingy's that stick up off the board, the markings say 560mf 16vdc. That is what the cap is rated at 560 micro farads at 16 volts direct current. The problem is in engineering....usually we design projects at 1.5 times the actual working situation to give a bit of a buffer or breathing room. These are not within those specs. Those caps are rated at 20% percent tolerance...giving the actual value swing from 672-448 mf and a working voltage of 19.2-12.8 volts...
Do you start to see the problem?????
The battery in a stable condition with alternator running is capable of running upwards of 14.8 volts after starting and usually settles around 13.8 volts while running. If the tolerance of the cap is close to the minus side in the value swing the working voltage is below what the actual voltage is and causes the cap to heat up and leak the oil that is inside loosing it's capability to filter out the noise.
Now for the second problem...checking various sources it is hard to find that specific cap in that specific physical size....12mm d x12mm L. So what I do is replace them with a 470 mf 25vdc cap that is the same size but with increased voltage rating and still within specs for the mf rating. This way you still get the filtering effect but with an increased working voltage with less chance of the cap getting cooked from too much voltage.

For those that want to try ...you can get the caps from Radio Shack and all you need is a soldering iron. Be careful of the physical size as with the covers on the amp the height of the caps can be no taller then 14mm. The 470mf 25vdc cap I mentioned is 8mm D by 14mm H and fits perfect. Just watch for the polarity of the caps...the board is marked for the plus sign and the cap will have a large black stripe down the side showing it's negative side.
For those not wishing to fix it themselves I can do it for you...I have yet to set a price as members have included funds to cover the repair ranging from 25-50...which is adequate for me.
Good Luck...

 

[trrgod]

I have an 89 coupe and the speakers have the whine in them. In the fronts I also get a loud hum.
I have heard that taking out the front speakers is a *****. Is there a trick to it or must I just struggle through it?
Who is Dr. Don?

 

[Tonylong]

btt - I think I'm having the beginnings of this same problem, and I want to follow this post

 

[vettedoc]

I have an 89 coupe and the speakers have the whine in them. In the fronts I also get a loud hum.
I have heard that taking out the front speakers is a *****. Is there a trick to it or must I just struggle through it?
Who is Dr. Don?

Dr. Don's is a radio repair service in Texas. I would take Eagle up on his offer and save some dough. This problem is very common in the Bose units of this era. Good luck


Doc

 

[Robertwav1]

Hey, eagle, thanks for the info on the caps. I don't have that problem but, that is some great information. Does that go for the "93" also? Is the configuration for the front speakers the same? Thanks again!

 

[Eagle85C4]

The same problem appears in all the Bose amps regardless of the year.
Can't tell you about the other years but on my 85 it is easier to just replace the whole door then try to replace the amp which is buried in there. Removal consists of complete dissasembly of the innards to get to the amp...

 

[Radar]

Hi Eagle,

Thanks for the advise. I am planning to open the doors up later this summer. I have a few car shows in June and July that I enter my car in and I don't plan to mess with it until they are over. I would appreciate your help then. Thank you for the kind offer and such fair prices!

Would the bad caps you describe be related to totally dead amps too? My system does this:

When I first turn the radio on, only my left front door speaker is on. The previous owner replaced that one with one of those non-bose amps from Mid America. It soulds weak and very tinny. Then after ten or twenty minutes, the right front door speaker and the left rear speaker come to life. The bass comes up real nice from those channels and it works good until I turn it off and it sits for hours. (the left front door speaker nevers gets any better - I think it is a poor match for the originals) Then the same thing happens all over again. The right rear is always dead.

Still want to tackle this for me?

Thanks,
Radar :confused

 

[Eagle85C4]

The caps will act ok till they start to heat up...then they go to ground...it will cause the amp to shut down till they cool off...

And I do not understand why someone would replace a bad amp with a non-bose amp...In most systems the amp is in the unit and it sends amplified audio to the speaker. In the bose the amp is built into each of the speaker enclosures and the unit sends it a line level signal which is amplified at the speaker.

Dig them out and I will look at them for you.

 

[Radar]

Eagle,

The non-bose amps are sold by places like Mid-America and Ecklers. There is a company that manufacturers a small circuit board that looks almost identical to the original Bose circuit board. It fits into the speaker enclosure just like the original. This after-market board does does not seem to have the same gain nor the frequency response of the Bose card. I think the former owner fell into that trap because it was less expensive. Luckly, I still have the old Bose card for that channel so we can see if it can be fixed.

Question: So a bad cap shorts to ground and kills the amp. My channels do the opposite, they are dead for about ten minutes and then all of a sudden come to life! Wierd. What could cause that?

Thanks,
Radar :confused

 

[Eagle85C4]

Could be loose connections, bad solder joints on the boards...any number of things could cause intermittent operations...

 

[rrhayden]

Eagle, advise please

I have a 92 with the boes system in it. Since I purchased the car the radio has worked, but seemed like you had to turn the volume knob up quite a bit to hear it. Last night on the way home I crossed some railroad tracks and all of a sudden the rear speakers blasted and sounded great. Then back to normal. This happened twice, I was thinking possibly I had a grounding issue and was going to look this weekend. Any suggestions as to what I should look for?

Thanks

 

[Eagle85C4]

sounds like a bad connection ...check all the connectors for any corrosion, clean all the grounding points....