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Discussion Starter #1
according to the pinout I found here, can someone confirm that to power on the Bose amp on the bench, I have to connect power to both Pin 1/10 and pin 19 (Control voltage). Of course with GND pin 2/11

And the NF signal pins are the actual amp input L and R.

1 Circuit 30, F4-16
2 Ground (W6)
3 Right rear speaker (H4/8) (-)
4 Left rear speaker (H4/7) (-)
5 Right rear door speaker (H4/4) (-)
6 Left rear door speaker (H4/3) (-)
7 Right front door speaker group (H4/2) (-)
8 Left front door speaker group (H411) (-)
9 Right NF signal (+) from A213
10 Circuit 30, F4-16
11 Ground (W6)
12 Right rear speaker (H4/8) (+)
13 Left rear speaker (H4/7) (+)
14 Right rear door speaker (H4/4) (-)
15 Left rear door speaker (H4/3) (+)
16 Right front door speaker group (H4/2) (+)
17 Left front door speaker group (H4/1) (+)
18 Left NF signal (-) from A2/3
19 Control voltage from A2/3
20 Fader switch (R26) (-)
21 Fader switch (R26) (+)
22 Fader switch (R26)
23 -
24 Right NF signal (-) from A2/3
25 Center fill tweeter speaker (H4/11) (-)
26 Center fill tweeter speaker (H4/11) (+)
27 Left NF signal (+) from A2/3
 

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Yes, applying power 1 & 10 & 19 while grounding 2 & 11 should cause it to power up. What I do in cases where I'm not sure about the pins is to use a multi-meter and check on the car which pins have power and what are grounded. In this case, pins 1 & 10 should have power as long as the key is on while 19 should have power only when the radio is on (and the key on).
 

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Thank you very much for your reply!

I do not yet have the amp on my car, but I am considering purchasing one. Other options would be a third party amp.

What bout the other pins?
NF signal is the input from the radio, for left and right speakers? This NF signal is displayed as A2/3, does that mean that it's pins 2 and 3 on A from the radio?

And what about the fader switch? R26?
 

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Wrong head unit radio for the 300SE, or wiring. The wiring is not even close. The 300SE is a 92/93 car. The link is close +94 cars, but the SL's and SLK's only use left to right controls(only two pairs come from the head unit), and have no rear to forward controls. The Sedans have four pairs of coming out of the head unit except for the 92/93 W140's.

Martin
 

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according to the pinout I found here, can someone confirm that to power on the Bose amp on the bench, I have to connect power to both Pin 1/10 and pin 19 (Control voltage). Of course with GND pin 2/11
Okay buddy. I just repaired one of these brick-amps for someone, and it was a pain to test as I did not have 92/93 W140, and my buddy had ripped-out his factory audio.

For starters, this is a two-channel input amp with some kind of mechanical fader that is challenging to test, but the fader function is controlled from the tuner .

Let me relabel this, so it easy to understand as I spun my wheels for a bit on the label.

The woofer channels have a very low cut-off frequency compared to any other modern Benz, or any +1994 W140, and the sensitivity is like -6dB compared to the other channels, so do not think the channel is burned-out if the volume is low. Remember every -3dB the power is cut in half, or +3dB the power doubles(this is for all audio).

The reason for amp failures is the leaking/dried capacitors for having dead channels, and the green ones leak first, and start eating the circuit board traces, and destroy the lead solder joints too. The traces/pads will look black.

The youtube's on this thread give you an idea how it is tested as a whole..

http://www.benzworld.org/forums/w140-s-class/1385821-aftermarket-radio-installation-thread-w140s-91-a.html



1 (+)12v Power
2 (-) Ground
3 (-) Right rear Woofer Speakers
4 (-) Left rear Woofer Speakers
5 (-) Right rear door Speakers
6 (-) Left rear door Speaker
7 (-) Right front door Speakers
8 (-) Left front door Speakers
9 (+) Right Input (Headphone level 2.5v Peak to Peak-Speaker level output of any car radio will work)
10 (+)12v Power (you need this one too together with the other)
11 (-) Ground ( Need this ground too with the other)
12 (+) Right rear Woofer speakers
13 (+) Left rear Woofer speakers
14 (+) Right rear door speakers
15 (+) Left rear door speakers
16 (+) Right front door speakers
17 (+) Left front door speakers
18 (-) Left Input (Headphone level 2.5v Peak to Peak-Speaker level output of any car radio will work)
19 (+) 12v Amp remote-turn-on
20 (-) Fader input **
21 (+) Fader input **
22 (Common) Fader input **
23 No wire connection
24 (-) Right Input (Headphone level 2.5v Peak to Peak-Speaker level output of any car radio will work)
25 (-) Center fill tweeter speaker
26 (+) Center fill tweeter speaker
27 (+) Left Input (Headphone level 2.5v Peak to Peak-Speaker level output of any car radio will work)

** The fader input, to test the amp outside the car it may work with no connection, but to properly test, or to install with an aftermarket head unit. I suggest you terminate the ends to a 10k ohm audio taper(pot) potentiometer(common to the center tap, and the others to each end of the potentiometer). The fader will fade from front to back...

If you need more help, I deciphered the pin-out to test each of the seven modules inside the amp.

Best of luck,

Martin
 

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Hello Martin, thank you very much for all the useful info!

However, I did not understand this part:

"I suggest you terminate the ends to a 10k ohm audio taper(pot) potentiometer(common to the center tap, and the others to each end of the potentiometer). The fader will fade from front to back..."

There are these three faders:
20 (-) Fader input **
21 (+) Fader input **
22 (Common) Fader input **

With "The fader will fade from front to back", you mean that I will adjust the balance of front vs rear speakers.
So for that, I connect a 10k ohm pot to Fader input (+) and Fader input (-), is that right?
If not, how do you mean "terminate the ends"?
And what about the (Common) Fader input?
And this part "common to the center tap, and the others to each end of the potentiometer"?
 

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Hello Martin, thank you very much for all the useful info!

However, I did not understand this part:

"I suggest you terminate the ends to a 10k ohm audio taper(pot) potentiometer(common to the center tap, and the others to each end of the potentiometer). The fader will fade from front to back..."

There are these three faders:
20 (-) Fader input **
21 (+) Fader input **
22 (Common) Fader input **

With "The fader will fade from front to back", you mean that I will adjust the balance of front vs rear speakers.
So for that, I connect a 10k ohm pot to Fader input (+) and Fader input (-), is that right?
If not, how do you mean "terminate the ends"?
And what about the (Common) Fader input?
And this part "common to the center tap, and the others to each end of the potentiometer"?
You are welcome,

These old W140s are really screwed up in audio design as one cannot grow with it(meaning add aftermarket components), so to test (or to install an aftermarket head unit radio) on these old W140's one looses the rear portion control in testing, or rear door speakers because the amp is only a two-channel input amplifier. With all it's original components connected(head unit, external radio tuner, and cd changer) one can get the front to back fade...

The pot is the only way to get the fader control with a aftermarket radio, or the sound will be balanced near the center.

+94 Mercedes or aftermarket radios give you quad output.

The SL's and SLK's also only use left and a right input source from the head unit. The woffer and Tweeters have no fade or left to right control-basically they are pre-set with the volume

Hope it makes sense.

Martin
 

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Discussion Starter #11
Just an update on mine, its out of the car, on the bench and disassembled.
I have made a list for the caps, but its been on hold for a while until I have a big enough order of other things I am fixing at the moment (peoples work always take precedence over your own work unfortunately).
The daughter boards look easy enough to recap (except under that plastic goo where it holds the Class D inductors, thats a pain to clean off and replace the tantalum cap).
Also, the motherboard is double sided, so that needs a bit of heat to get the components de-soldered.
One plan of attack is to test each daughter board with an extension cable to the motherboard.. it makes it easier to scope and debug, if the recap doesnt fix the main problem.
once all daughter boards are tested working, will reassemble and do a final check.
 

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Just an update on mine, its out of the car, on the bench and disassembled.
I have made a list for the caps, but its been on hold for a while until I have a big enough order of other things I am fixing at the moment (peoples work always take precedence over your own work unfortunately).
The daughter boards look easy enough to recap (except under that plastic goo where it holds the Class D inductors, thats a pain to clean off and replace the tantalum cap).
Also, the motherboard is double sided, so that needs a bit of heat to get the components de-soldered.
One plan of attack is to test each daughter board with an extension cable to the motherboard.. it makes it easier to scope and debug, if the recap doesnt fix the main problem.
once all daughter boards are tested working, will reassemble and do a final check.
The tantalum cap is 10uF at 35v

Those green ones leak like crazy...

This is super helpful too:

Bose Amplifier Repair Notes Rev 3/14/02 Gary James

Enjoy..

Martin
 

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Yes, that article was a big help when I did my amp 14 years ago. I compiled a list of capacitors used in the Bose amp, all were available from Digikey. Some of them may not be available anymore, or have different part numbers.
Mike
 

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Discussion Starter #14 (Edited)
Thank you Mava.
Yes I have already seen that schematic before and the Class D boards (4 out of the 7) are indeed based on it.
The other boards are just Class A/B design..

Maybe now is not the time to bang on about how much I dislike Class D design principles :p
 

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Thank you Mava.
Yes I have already seen that schematic before and the Class D boards (4 out of the 7) are indeed based on it.
The other boards are just Class A/B design..

Maybe now is not the time to bang on about how much I dislike Class D design principles :p
You are welcome

I'm a power electronics guy by education, so these Class-D are no more than switch-mode power supplies, and one has to use low-ESR caps. Everything today has a switch-mode supply in it...Nearly every flat screen TV has a Class-D audio system...

Hope you get it fixed..

Martin
 

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Discussion Starter #16
Know them well, but I am also a HiFi nut, and my problem with Class D is this, and I quote:

"It is our belief that enough damage has already been done to the signal. Why screw it up even more by converting to another format and then have to convert back again?"

and to end my rant, everything is repairable :)

You are welcome

I'm a power electronics guy by education, so these Class-D are no more than switch-mode power supplies, and one has to use low-ESR caps. Everything today has a switch-mode supply in it...Nearly every flat screen TV has a Class-D audio system...

Hope you get it fixed..

Martin
 

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Discussion Starter #17
Q: any easy way to get that solid goo off the tantalum so it can be removed?
what have people used in the past to remove?
cheers.
 

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I just remove the solder off all the neighboring(like 6 or 8 caps there) electrolytic's, and the whole thing will roll up like a carpet after a prying off, yet to do one cap at a time one has to cut the goo off.

Hope it helps,

Martin
 

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We have a capacitor replacement program (preventative maintenance) here at work: we never replace tantalum caps. Are you sure that it is needed?
An old tantalum is worse than a leaking electrolytic as Tantalum's like to go into low resistance mode which will intensify the trouble shooting-like pulling the whole circuit to ground from the +V rails to ground :eek

In my book of repairing switch mode supplies, Guitar, and Movie theater audio amps. I take those suckers out of the equation....

Martin
 
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