Heated window interferes with radio

[S500 Pete]

Hi,

Misty mornings lately and I've noticed that when I use the heated rear window on my E500 the radio (Command unit) just turns in to a big hiss. I guess that there is a capacitor or similar somewhere between the aerial and the heater wiring that has failed.

Any idea if this is the likely solution

How much and how hard to fix?

I have a bit of the Merc used car warranty left, would this be covered?

 

[television]

I am sending you the test for the rear window

 

[brandwooddixon]

There's an amplifier behind the offside C pillar trim (same side as the wiring disappears into) that can fail.

Unless you have folding rear seats you'll need to remove the seat back to remove the pillar trim if you look at replacing it.

I think that it costs about £20 if my memory serves me right.

 

[bigasotonuk]

There's an amplifier behind the offside C pillar trim (same side as the wiring disappears into) that can fail.

Unless you have folding rear seats you'll need to remove the seat back to remove the pillar trim if you look at replacing it.

I think that it costs about £20 if my memory serves me right.

Hi,
This amplifier I believe is generic across many models of MB with the aeriel in the rear window, and I have recently got a quote for one of £34 not sure if theres VAT to pay on that.
You will have to remove the internal 'C' piller trim on the passenger side to expose this amplifier, but it is only plug and play.

 

[television]

But the amp has nothing to do with the rear window, if FM is good when the window is not on it would not be the amp.

The info that I have sent shows how to connect a lamp in place of the window to test

 

[brandwooddixon]

So the amp doesn't do any filtering on the signal?
I didn't know that.

Or is the problem more to do with the supply to the heater?

 

[bigasotonuk]

Hi,
The amplifier has a power supply and there is a smoothing capacitior in the same area though I "think" this cap is on the window heater supply, so it maybe a faulty cap on the window heater supply causing inerferance to the radio, possibility?
I have recently noticed a degedation in sound quality on radio in my C43, which seemed to coincide with me fitting a Parrott Bluetooth kit, I have put this down to a possible broken centre pin in the aeriel connector at the stereo, due to being plugged/unplugged a good few times and to be a known fault, I have bought a new aeriel lead from MB, this will replace the aeriel lead from the head unit to the aeriel Amplifier behind the "C" piller trim.
Please post back on what you find as it may assist me in my diagnosis.

 

[television]

So the amp doesn't do any filtering on the signal?
I didn't know that.

Or is the problem more to do with the supply to the heater?

Our cars have to have an antenna amp as they are wired in 50 ohm cable and the signal needs to be pushed through via the amp, or they would be too weak.

The rear screen contains the antenna and the heated part. As the heated part is only a conductive film, it can set up arcing that feeds back into other components. Yes some cars do have a 15.000 mfd cap to suppress the crackle, that must be fitted as near as possible to the source on interference.

This type of interference is very spiky and difficult

 

[S500 Pete]

I am sending you the test for the rear window

Thanks Malcolm, I've received the test

If it is likely to need a new rear window I hope that it might be covered on the warranty. Otherwise I'll listen to CDs while the window clears

 

[television]

Thanks Malcolm, I've received the test

If it is likely to need a new rear window I hope that it might be covered on the warranty. Otherwise I'll listen to CDs while the window clears

If you can fix up that test and it proves it,,then yes a new screen

 

[Blobcat]

Quite a few 211's had rear windows replaced because of the interference from the screen heater, mine included.

 

[television]

Quite a few 211's had rear windows replaced because of the interference from the screen heater, mine included.

This has been ongoing since my very first post,it was all 140's then and the 126 and the antenna was not in the screen on those

 

[S500 Pete]

Quite a few 211's had rear windows replaced because of the interference from the screen heater, mine included.

Thanks for that, more ammunition if I need a rear screen.

 

[Kevin Dawson]

Hi Malcolm,

Could you please send me the test too, my W204 has just started with the same fault, severe degradiation of signal when the rear heated window is activated.

Kind regards,

Kev Dawson

 

[television]

Sorry this test will not do for the 204, all one can do is to replace the rear screen of try a 20,000mfd cap over the screen wires as close as possible to the rear screen connectors