W124 Occasional loss of speakers?

[brucemillar]

Guys

On my 124, I occasionally lose all speaker output? It is almost as if the radio has been muted!! All speakers just stop, nothing, nil, zilch, not even a background whisper of hiss.

I know that this is not the head unit as I have the same issue with other units I have tried (and they are different makes).

There is no pattern to when this will happen. It just does. The latest episode is with the car sat on axle stands in the garage > radio playing and then >>>> Nothing, silence. The head unit stays correctly illuminated and displaying the station etc. Switching to a CD has no effect. We remain muted.

I currently have the car playing only via the front dash speakers. The wiring to these, is the stock MB wiring that has not been changed, with the small blade plugs in each channel just behind the head unit.

There is a mute wire (white) on the Euro Connector. I have taped that and ensured it is not shorting.

I also have the fade wheel for the rear door speakers. This is not in use as these speakers are disconnected for testing.

When it is working! It is absolutely fine. Then with no warning or movement it will just cut out and can stay like that for days only to return when it feels like it.

Any suggestions?

I am thinking an earth problem. But how to test this?

It has been suggested that the electric antenna may be a weak spot, but could this mute the speakers?

I am more on the side of this actually being a mute action, given how it only cuts the speakers and all media, CD, Radio etc.

 

[whitenemesis]

Certainly points toward the output stage, as any fault in the signal/input would give hiss.

Could be a failing output amp transistor, even a cracked PCB track, output socket solder joint

 

[brucemillar]

Thank you. But it is happening in more than one head unit. If I pull the head unit now and replace it with another, I still have no sound? Is there another amp that I do not know about in the 124?

 

[whitenemesis]

Ah, erm .....

There are a few posts regarding problems with the separate fader switch?

Might this be of use?

PeachPartsWiki: W124 Stereo Removal Process

 

[grober]

http://w124-zone.com/downloads/MB CD/W124/w124CD1/Program/ETM/ETM.pdf
page 89 onwards
there can be another amp on later models-- or it could be some weird fader fault -- really depends on how much of the old wiring remains connected.

 

[brucemillar]

Graeme

I have a 1987 car This narrows down the search a fair bit. The simplest thing appears to be to run a 'good' earth to each part in turn. If this fails then the fader switch/wiring has to be suspect as that is a common part.

Somethings to be getting on with. I wanted it running for Benz on the Green as Mrs Millar will not want to be listening to me all the way there and back.

 

[Ted]

Got me stumped, Bruce.
I don't think it is an earth as outputs are usually 'floating'. The four way balance pot also shouldn't need an earth.
The stereo stays on, so that suggests that it is finding an earth from somewhere - they sometimes earth via the aerial ground wire but that usually results in terrible interference.
Some head units show when they are muted so you may be able to eliminate that.
I'll mull it over and post if I can think of anything.

 

[brucemillar]

Ted Thank you. I have seen people mention that if a speaker wire shorts out? It can mute the system. The same is said at the fader. I think I will pull the fader out and clean and inspect it. It is a prime candidate for collecting crud. The head does not show it is muted (it could, but it does not).

Sent from my iPhone using sausage fingers.