Mercedes-Benz Forum banner

21 - 39 of 39 Posts

·
Registered
1994 E420
Joined
·
15 Posts
Thanks for getting back to me so quickly.
Yes, I did make sure to have the stripe on the new capacitor line up with where it was on the old one. Does anyone know if there is a continuity/resistance test for pins on the amp? that may show me if one of my connections is bad.
Thanks!
 

·
Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
Joined
·
8,729 Posts
If the amp was working before the repair albeit badly, it should have worked after the caps were replaced, again albeit badly.

I would double check that nothing has come adrift like a wire or that solder has not run across making a bridge to another component.
 

·
Registered
1994 E420
Joined
·
15 Posts
After opening the amp up again, I found that I melted part of the PCB while desoldering. I've ordered a replacement, and intend to use it as a model to get the old one back together. Thanks!
 

·
Moderator
93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
Joined
·
7,949 Posts
Sometimes when fixing these amps.

One can blow-up the BOSE chips on the power section, and have done it...

When I have to replace those BOSE chips. I just steal them from the 90's C-class cars amps, and in a pinch the C-class amp can be used, but the pins on connector-head on the car has to be changed as the woofer is on another channel, but electrically it very close...

Martin
 

·
Registered
1994 E420
Joined
·
15 Posts
Martin,
Thanks for the information. I gave the DIY a shot, but ended up just replacing it with an ebay purchase. Next time it bites the dust though, I'll try again!
 

·
Registered
SL 500 1995
Joined
·
22 Posts
I have problem with my Bose amp from 1995.I have the car since 2010. In the winter car is standing in the garage. Every spring I hear crackling in the speakers. It takes only a few days . After few days crackling stops and the sound is clear. Two years ago, subwoofer stopped working.

Yesterday my friend put 8 new capacitors to the amp. Quick test... Subwoofer still not working, speakers crackling.

I think that the speakers in the door can be moist and the situation does not have a connection to an amplifier ?

What else can we check in the amp?

Thanks.
 

·
Moderator
93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
Joined
·
7,949 Posts
I have problem with my Bose amp from 1995.I have the car since 2010. In the winter car is standing in the garage. Every spring I hear crackling in the speakers. It takes only a few days . After few days crackling stops and the sound is clear. Two years ago, subwoofer stopped working.

Yesterday my friend put 8 new capacitors to the amp. Quick test... Subwoofer still not working, speakers crackling.

I think that the speakers in the door can be moist and the situation does not have a connection to an amplifier ?

What else can we check in the amp?

Thanks.
The woofer amp channel can be tested with another speaker as it has this little two pin connector from the big connector. It is about 14cm away.

Next, the woofer channel is the lower left circuit with the connector block facing left too. It can be open/shorted c4815/c4816/c4818 or U14. U14 is not available, but I have used them from other Mercedes amps.

Some rare cases Q4801-Q4804 Crack or Short

I all else fails, a C-Class amp will work, but the connector head on the harness at the amp must dissembled, and few pins swapped

Martin
 

·
Registered
1997 SL500 70K Miles
Joined
·
281 Posts
There are two things to be concerned about on this and pretty much any aging amp. The first is that the electrolytic capacitors have dried out and may or may not have leaked with age. A bad capacitor can be evaluated with an esr tester, often without even removing the capacitor, and these testers are available rather cheaply, but capacitors are just plain cheap and can be replaced at very little cost, so why not. It is not a bad idea to go ahead and replace all electrolytic capacitors on a 20 year old amp if one is so inclined. Particularly the power supply caps which are larger in uF and are closer to where the power comes into the circuit (12V in auto amps). Electrolytic capacitors are easily identified, they are cylindrical in shape.

The second item of concern with an amp is cracked solder joints due to thermal cycling. The transistors on this and other amps heat up during use and the repeated heat cycling can cause problems, cracking the solder connections. Identify and reflow the solder on all transistors. If the transistor has a heat sink on it, even more so.

Thought not technically part of the amp, potentiometers such as the volume controls, bass and treble controls, are troublesome and can be cleaned with a high quality spray such as Deoxit. In fact, don't use anything else.

Following advice in this post should address a vast majority of issues associated with amps and electronics in general. If not, the issue is probably a bit difficult to troubleshoot, but many good techs have identified specific issues and one can frequently fix recurring issues not so easily identified by a novice.
 

·
Registered
1994 SL500 1998 SL600
Joined
·
151 Posts
Thanks for this thread! Very useful!

I already upgraded the 8 big capacitors but I didn't solve the problem, still half of the speakers are producing high pitch squeaky noises.

At a closer inspection almost all the little 16V 10uF have leaked, in particular on the pre amp board.

My question is, how do I remove that board from the base metal panel? It's kind of glued to a black polyurethane layer.
 

Attachments

·
Registered
1995 SL 500 2017 AMG GLC 43
Joined
·
934 Posts

·
Registered
1994 SL500 1998 SL600
Joined
·
151 Posts
Those are really too cheap!!!! Got few packs on Amazon with one day delivery.

But my previous question is still unanswered:
"how do I remove the pre amp board from the base metal panel? It's kind of glued to a black polyurethane layer."
 

·
Moderator
93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
Joined
·
7,949 Posts
Thanks for this thread! Very useful!

I already upgraded the 8 big capacitors but I didn't solve the problem, still half of the speakers are producing high pitch squeaky noises.

At a closer inspection almost all the little 16V 10uF have leaked, in particular on the pre amp board.

My question is, how do I remove that board from the base metal panel? It's kind of glued to a black polyurethane layer.
You are welcome,

Now those 8 capacitors MUST be LOW ESR type as this is a Class-D Amplifier. One does NOT put any capacitor. It must BE low ESR Caps that are used in Switch Mode Power Supplies-AKA like a computer power supply...

Next buy reputable capacitors, and they must BE FRESH-NO ebay/Craiglist/Amazon deals

In the USA for the average JOE the only two places are Mouser Electronics Huston TX and DigiKey in Minnesota. Around the world Farnell. Those are the places for small quantities... Must be 105c, so they last

Small signal ones can be Panasonic FC series through out both boards, but the pre-amp can use audio grade for low leakage. I commonly use Nichicon UVZ for all the capacitors except for the large 8. Those I use the Nichicon FC series as that was used on these amps to give them the same life.

I'd replace all the electrolytic capacitors as the picture is from a 94 R129 that had continuous noisy sound on two channels, and the picture one can see the corrosion on the solder pads on the very upper right capacitor, and the one on the near center behind C5021, and the two capacitors behind the balancing blue trim pot.

Here is the list and location of capacitors on the R129 +94 Audio Amp.PDF scan. The black dot on each capacitor on the drawing is the negative lead location. These Electrolytic Capacitors are polarized, so putting them backwards will cause them to vent/explode/get real hot too

To DIY it can be done with patience with a soldering IRON(Not a soldering GUN!!)The part of the battle is getting fresh capacitors that way you fix this amp once every 15 years or so not the next year like someone posted... Sadly on the R129 AMP ALL the electrolytic can capacitors need to be replaced. To keep track do one at a time(remove one - install one) not remove all of them, and then replace all of them

The Pre-Amp has double sided foam tape, I use door card plastic spoons to separate the pre-amp. I use the left and 2nd to the left tool.

https://www.harborfreight.com/5-piece-auto-trim-and-molding-tool-set-67021.html

It also has three key/twist locks that one has to use pliers to release on the pre-amp..

Lastly, you are spinning your wheels with any capacitors as you can blowup the BOSE driver chips.

Martin
 

Attachments

·
Moderator
93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
Joined
·
7,949 Posts
Thank you MAVA... I think I have this...
People who live in hot areas suffer from pre-amp leaking capacitors, or people with very hot summers.

Once one leaks it is just wise to replace all of them.

Martin
 

·
Registered
1995 SL 320
Joined
·
65 Posts
I took the amp to a guy who repairs radios, etc and he put to amp on his bench and says that the outputs are good. He was pleasantly surprised that my capacitors looked good... I have tested the wiring going to my amp at the harness and got these results. Thoughts?
 

Attachments

·
Registered
96 S320 02 CLK55
Joined
·
55 Posts
People who live in hot areas suffer from pre-amp leaking capacitors, or people with very hot summers.

Once one leaks it is just wise to replace all of them.

Martin
Mava are you still repairing these amps ? I sent you a message.
 
21 - 39 of 39 Posts
Top