E51 Head unit interference - 06' E51.

Mike Anderton

Newbie
E51 Owner
#1
Without any obvious cause the Radio/CD player of the main head-unit has started playing up. Basically, it sounds as though there is severe interference going on. Happens with both radio and CDs (haven't tried the minidisc).

We have an upgraded DVD player installed fitted in the glovebox (in when I bought the car), but this plays DVD(PAL)/CDs fine.

So, as the DVD player plays OK, I've deduced the problem isn't with the speakers or the aerial and the amp must be OK too??

Any ideas on what could be causing this would be greatly appreciated!!
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
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Premium Member
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E51 Owner
#2
I’d pull dash apart and see if there are any obviously damaged wires or connections. It may have been put back in carelessly to sell car.
If nothing obvious I’d get a replacement from a breaker and try that. Or if your budget stretches to it a new aftermarket headunit.
 

Whotsit

Well-Known Member
Premium Member
E51 Owner
#3
Suggest you remove the radio and make sure that you have a good ground (earth) but it would pay to put new grounds on any way, with regards to the ariel that needs to be grounded as well, very important.
 
Last edited:

Alan Morgan

Here for life
Premium Member
E51 Owner
#4
@Mike Anderton
Without any obvious cause the Radio/CD player of the main head-unit has started playing up. Basically, it sounds as though there is severe interference going on. Happens with both radio and CDs (haven't tried the minidisc)
A couple of questions:
a. you say 'started playing up' - so can we assume it was OK at some stage prior to this?
b. The Radio/CD player - is this the OEM system or an after market system?

Suggest you remove the radio and make sure that you have a good ground (earth) but it would pay to put new grounds on any way, ........
Good advice

.....with regards to the aeriel that needs to be grounded as well, very important.
That's not so straight forward if the Radio/CD player is the OEM one as the OEM aerial socket is a 2-pin type and not the 'normal' UK ISO variety.

As a general suggestion, if the Radio CD player were working beforehand, has there been any work on the vehicle that may have disturbed the wiring or caused a loss of power (or connection) to the OEM radio antenna amplifier.

The severe interference - is this with the
  1. engine running?
    or
  2. ignition ON but no engine running?
    or
  3. ACC only ON?
 

Whotsit

Well-Known Member
Premium Member
E51 Owner
#5
Mike Anderton, I have just reread you posting I had assumed you or previous owner had replaced the head unit and it had only just started playing up, but if it is still the original japanese one you have are you sure it is not just "white noise" ? Now a silly question, you are aware that if it is oem you are not going to get other radio stations than radio 1
 

Alan Morgan

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Premium Member
E51 Owner
#6
Mike Anderton, I have just reread you posting I had assumed you or previous owner had replaced the head unit and it had only just started playing up, but if it is still the original japanese one you have are you sure it is not just "white noise" ? Now a silly question, you are aware that if it is oem you are not going to get other radio stations than radio 1
Radio 2 actually, or at least that's the case without a band expander.

Some while back I knocked up the diagram below to help understand the OEM VHF radio issue - in short:
  • The OEM radio is designed to receive FM signals 76-90Mhz
  • The UK frequencies for FM services are 88-108Mhz
  • Without a band expander the OEM radio will only play UK FM frequencies in the range 88-90Mhz, i.e. Radio 2
  • A band expander fits between the OEM radio and the OEM (2-pin) antenna lead and 'down shifts' the received UK FM frequencies so that they 'play' on the OEM radio.
It's not a perfect solution but gives the OEM radio some use.

What I do not know about, are the frequency characteristics of the OEM Radio Antenna amplifier. It's reasonable to expect that the 'band pass' characteristics of the amplifier are not idea for UK frequencies. This may explain why some 3rd party replacement head units give adequate radio reception (Xtrons for example) whereas some Pumpkin units seem to be problematic.

temp.jpg
 

Whotsit

Well-Known Member
Premium Member
E51 Owner
#7
To be honest Alan I couldn't remember whether it was radio 1 or 2 that was the lower frequency when I was typing it not my sort of music generally speaking so took a gamble on it and and lost out but the point was that if he doesn't know the difference between white noise and interference he could easily become confused, also my ref to grounding the antenna is applicable because if another head unit had been fitted then a conversion aerial cable would probably have been used and that is terminated in a standard car aerial plug of which the outer contact go to ground on the head uni, however without further information I doubt a successful answer will be arrived at unless by guesswork.
 

Mike Anderton

Newbie
E51 Owner
#8
@Mike Anderton


A couple of questions:
a. you say 'started playing up' - so can we assume it was OK at some stage prior to this?
b. The Radio/CD player - is this the OEM system or an after market system?



Good advice



That's not so straight forward if the Radio/CD player is the OEM one as the OEM aerial socket is a 2-pin type and not the 'normal' UK ISO variety.

As a general suggestion, if the Radio CD player were working beforehand, has there been any work on the vehicle that may have disturbed the wiring or caused a loss of power (or connection) to the OEM radio antenna amplifier.

The severe interference - is this with the
  1. engine running?
    or
  2. ignition ON but no engine running?
    or
  3. ACC only ON?
Interference happens all the time. The only noteworthy point is that, for ~1 second or so after turning the radio/cd player on, the sound is fine. However, after this, the interference begins. The Radio/CD is factory fitted. The DVD/CD player in the glove box is aftermarket (fitted by previous owner - and sound is fine with this device).
 
#10
Hi Alan,

It's the same with both ignition only or engine on.
What is the ACC please?

I've noticed the sound is fine for the initial second you turn the radio/CD unit on, but after that the interference starts.

The only change that may be responsible is the radio band expander that was fitted by the garage when I bought the car. However, it worked fine initially.

Thanks for your help with this issue!
 

Alan Morgan

Here for life
Premium Member
E51 Owner
#13
  • @Mike Anderton - ok, thanks for the info - I wish you were nearer as it's difficult to deduce the finer points of what's happening with your setup:(
  • you have said that the 'upgraded CD/DVD player' works fine but the OEM Radio/CD Player when switched on, gives rise to the interference
  • In simple terms I would initially summise that the Upgraded player feeds it's signal to a power amplifier and then the loud speakers
  • The OEM Radio/CD player works in a similar way, i.e. it's output also goes to a power amplifier and then the loud speakers
  • QUESTION (1)- do the upgraded player and OEM Radio player use the same audio power amplifier and speakers do you know? If they do share the same Amplifier etc, I'm wondering where the upgraded player and OEM Radio/player signals meet up - some sort of audio switching device maybe?- and if there is such a switching device, has the input from the OEM radio/player become detached and is thus just feeding 'white noise/interference' into the amplifier? Below is a conceptual diagram of what I'm thinking of
  • QUESTION (2) - is the noise/interference from the OEM radio/player present when playing a CD or just when on Radio? (and I'm assuming that the noise/interference goes if the OEM radio/player is switched OFF? - please confirm).
amp-1.jpg
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
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E51 Owner
#14
I’d be tempted to try another headunit to confirm it’s not an internal fault in headunit. Along the lines of what Alan is suggesting above but I think even Bose system with external power amps do the line level source switching in side the headunit.
 

MrRob_in

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#15
Ie oe audio feed is

ExDVD/CD - *Rear Phono/RCA - TV Module - Nav Module/DVD - Headunit/radio/CD - AMP - Speakers

*Additional source switch would go here.
 

Alan Morgan

Here for life
Premium Member
E51 Owner
#16
Ie oe audio feed is

ExDVD/CD - *Rear Phono/RCA - TV Module - Nav Module/DVD - Headunit/radio/CD - AMP - Speakers

*Additional source switch would go here.
  • I agree Rob, that that is the normal signal path one would expect. (as per the diagram on P210 of the JPNZ workshop manual)
  • That same diagram implies that the audio amp is part of the Radio/CD (aka Electronic tuner radio)
  • Obviously some switching takes place in this unit i.e. either the the OEM Radio/CD signal or the Upgraded DVD/CD player signal is passed to the amplifier
  • This does indeed bring us back to your suggestion that the fault lays in the Electronic tuner radio (what we call the OEM head unit)
 

MrRob_in

Part of the furniture (please de-cat your e51/2)
Staff member
Premium Member
E51 Expert
E51 Owner
#18
I think the Bose system gets external (to HU) amps but as op doesn’t mention it is a Bose system I assume it is an internally amped headlight. Whatever the audio path is through the HU and problems only occur on it's internal sources so it’s likely problem is there.
 
#19
  • Mike, can you clarify something please - are you saying that at some stage that the Radio/CD player worked fine and DID NOT cause any issues?
Hi Alan,
Yes, the radio/CD player worked fine until a few weeks ago, when all of a sudden the interference started.
The Rear Phono/RCA has never worked since I bought the car. I was told by the garage this is because the DVD player was upgraded (to a PAL compatible player). Not sure why this is the case however!
Do you think the interference could be anything to do with the FM expander. This was fitted when I bought the car 3 months ago from the garage and I wondered if the connection could have become loose?
 

Len

Active Member
Premium Member
#20
Just to add to the confusion, it sounds like a capacitor has been cooked. Where? Who knows without checking it out. I would suggest a radio repair facility and give him the headache.