Radio Interferance

[TheMcBain92]

Hi All

I have recently bought a 2006 Mondeo ghia 2.0 TDCi which has the Sony 6cd head-unit. I have a couple of faults regarding the sound system which i'm hoping someone can help me with.

Firstly, the passenger speaker has developed a slight crackle at high frequencies but also it cuts in and out like there is a bad connection somewhere. I have had a look behind the door card but with the Speakers being part of a larger unit i didn't want to dig much further until i have had the head-unit out to check the connections there first (waiting on delivery of the keys to remove it).

Is there a known problem with wires coming lose or Speakers failing in this way?

Secondly, I have very poor radio reception on both am and fm, but it sounds more like some sort of interference as it is constant (still present when my previous car would have a good signal). The sound of the interference changes but never disappears.

I am thinking it my be some sort of electrical interference, as i found out this morning when trying to listen to an AM station, that when i press the button to cycle through the trip computer i get a burst of interference each time i press it.

I have read on other posts the the first check should be to check the base of the aerial behind the interior light which i will do when i get home, but with the symptoms i have regarding the trip button i though i would create a separate topic.

BTW, cd playback seams unaffected by this interference.

Thanks in advance

UPDATE: After doing some investigating and a check of the aerial (which wasnt too bad) i descovered that the interference is only there when the ignition is turned on. If i have the ignition on and then turn it off after about 20 seconds the interference goes away. I also tried with the radio on different frequencies and the interference come out as whistling/squealing sound.

I have a video but its not very clear. Will upload if requested.

[BOF]

Firstly, the passenger speaker has developed a slight crackle at high frequencies but also it cuts in and out like there is a bad connection somewhere. I have had a look behind the door card but with the speakers being part of a larger unit i didn't want to dig much further until i have had the head-unit out to check the connections there first (waiting on delivery of the keys to remove it).

Is there a known problem with wires coming lose or speakers failing in this way?

Well, your description sounds like a 'speaker which has been overdriven and the voice coil is now scraping against the magnet. Could be a problem with the wires, but usually it isn't.

Secondly, I have very poor radio reception on both am and fm, but it sounds more like some sort of interference as it is constant (still present when my previous car would have a good signal). The sound of the interference changes but never disappears.

I am thinking it my be some sort of electrical interference, as i found out this morning when trying to listen to an AM station, that when i press the button to cycle through the trip computer i get a burst of interference each time i press it.

Well, two things:

• check the wiring - if the power supply to the antenna is bad (low voltage/high resistance) it will definitely cause this, as could a poor antenna (signal) connection. You may want to take a voltmeter to the supply to the antenna and see what that reads.
• beyond that, it might be the amplifier in the base of the antenna (I assume) - i had this go in a previous car, and the radio reception was always cr4p, until I replaced it. Fortunately, aftermarket ones aren't that expensive (for that car GSF had one, reasonably priced, but they may or may not have them for Fords).c.

BTW, cd playback seams unaffected by this interference.

That's what you'd expect if the problem was on the RF side (antenna, cable to head unit, head unit itself).

UPDATE: After doing some investigating and a check of the aerial (which wasnt too bad) i descovered that the interference is only there when the ignition is turned on. If i have the ignition on and then turn it off after about 20 seconds the interference goes away. I also tried with the radio on different frequencies and the interference come out as whistling/squealing sound.

This now sounds like electrical interference, probably on the battery voltage line, getting from the interference source into either the Head Unit or the Antenna amplifier unit. These problems can be tricky, and you'd really like to know what happened just before it went wrong (but you probably can't find that out). The pragmatic approach is just to scatter capacitors at various points (either close to the presumed interference source or close to the interference victim). Just be aware that if you do go down that route, bigger isn't necessarily better - just the opposite, in fact.

One worthwhile experiment might be to take a normal portable radio into the vicinity of of the car and see whether that gets interfered with, too. You might even be able to localise the interference source somewhat by moving the portable around.

[TheMcBain92]

Hi thanks for the quick reply.

For the first problem i'm guessing if i don't find any connection problems behind the head-unit then a new speaker is required.

As for the second problem you mention an "Antenna amplifier unit." I was wondering if you would know where i could find this unit, is it behind the head-unit somewhere? Also what size capacitor would you recommend?

Also would trying a different head-unit be useful to rule out the original being faulty?

[BOF]

For the first problem i'm guessing if i don't find any connection problems behind the head-unit then a new speaker is required.

Yes. I'd probably take the opportunity to try to get a decent speaker,or Speakers, but, to be frank, the mounting position probably does more than anything to limit the amount of bass, so there is a limited benefit. And, remember that the low frequencies and high frequencies are already split, so any higher frequencies out of the lower frequency unit (ie, out of a co-axial tweeter) are wasted. So the 'component type' speaker rather than the type with the smaller tweeter cone is required. I've no idea what the original Speakers go for, either new or from someone selling them on, on eg e-bay or a breaker.

As for the second problem you mention an "Antenna amplifier unit." I was wondering if you would know where i could find this unit, is it behind the head-unit somewhere? Also what size capacitor would you recommend?

I haven't, to be honest, looked at a mondy one, but the usual arrangement would be for it to be in the base of the antenna. It should be pretty apparent, if you get the headlining off. There is probably an erffing big nut on the underside holding the antenna down (pulling it down on to the compliant mechanical seal) with the wires coming through the centre of the bolt.

A capacitor 1 nF to 10 nF would be a good start - you could try 100 nF, if that doesn't help, but most likely if the lower values don't work at all, the higher one won't either. (Maplins WX68Y to WX77J would be typical examples, if that helps). It is only really worth playing with values or the arrangement (for example, you want short leads, but where to connect to - a ground wire, or the car bodywork, and how short can you reasonably make those leads without having to connect to the wrong ground?) if adding the capacitor changes the result, but not enough.

As well as a shunt capacitor (capacitor between the supply and ground) it is possible to use a series inductor, in the form of a clamp-on ferrite (Maplins N89AB and so on), but let's hope that much playing around isn't necessary.

Also would trying a different head-unit be useful to rule out the original being faulty?

Well possibly. But a head unit is expensive (unless you have one hanging around, already), and an antenna unit is cheap. Also, the antenna unit is more likely to get damaged by external electrostatic discharge (although the HU is quite complex, so that might change the overall reliability, too).

If you aren't getting anywhere, ask again because there can be a lot of 'trial and error' in getting this to work.

[TheMcBain92]

I don't think the standard ones are that expensive if i remember rightly when i looked the other day.

As for the aerial then i will have to do some more investigating as there is only the antenna cable bolted onto the bottom of the aerial base.

Fortunately i do have a spare unit lying about from my previous vehicle so i will try that.

As for fitting the capacitors, that will have to wait for some decent weather and some spare time.

Will keep updated.

[BOF]

As for the aerial then i will have to do some more investigating as there is only the antenna cable bolted onto the bottom of the aerial base.

Two (or three) things come to mind:

• It would be handy if someone who had actually seen the mondy system would turn up and tell about what they have seen, because, as I say, I am familiar with the general system, but haven't seen the mondy one (or, alternatively, a link to an exploded diagram of that area of the car). Certainly the active/amplified system ought to have a power supply (there is a way that power could be transmitted over the central connection of the co-ax cable, but I don't know of a system that actually does that...it would make sense, though).
• It is also possible (but, perhaps, not likely) that the Ford-brand system is different from the system with the Sony Head Unit. Certainly, the Sony branded system seems to have changed, once it got DAB, with a separate co-axial cable for the 'normal' signal and the DAB frequency range signal.
• If the car originally had an amplified antenna, and it has been replaced by a passive one, you might get exactly the symptoms that you outline - poor signal, making interference more likely. I don't know that is what has gone on, but it is a possibility that it would be nice to rule out by someone who has seen the system giving us the low down.

And yes, this kind of messing about with cars is better in better weather.

[TheMcBain92]

The removal tools finally arrived the other day so i finally got chance to remove the radio. The large quadlock connector looked connected properly but it appears that someone has used a different connector at some point as there was a lot of push connectors.

The single aerial plug looked in good condition and was connected. I decided to do a bit of an experiment to see if the interference was still there with the aerial cable disconnected and it wasn't. Does that indicate that the interference is coming down the aerial cable or was it missing just because there was no signal for it to interfere with?