Radio sound

[Themoog2]

Someone explain this if possible..
Anyway the sound from the radio is tinny with no bass - but only during the winter. Summer is ok and it sounds normal.
I thought it was a bm24 fault so sent it off for repair but I've just put it back and it's no different.
Cds sound is OK it's just the radio. What's going on? Any ideas..

[Themoog2]

I forgot to mention that when the rear defroster is switched on it totally wipes out the radio signal

[henrym3]

My bet would be you have a break in your aerial/window lines, which shrink in the cold and expose the crack/break. Or a bad aerial connection somewhere

[Themoog2]

If that's the case, why would it only affect the bass? It sounds like some of the speakers are not working but as soon as I switch to cd it's fine.

[X5Sport]

As you have had the amp looked at then I would have suggested it might be damp cones until you said it’s fine in CD mode. Might be worth a check of the tone settings for the radio in case they vary with audio source? Not sure why it would be seasonal though.

If the demister is also causing an issue then it could be the radio itself, or the aerial system (weak signal).

It might just be that the radio is ever so slightly drifting off tune enough that for FM Stereo the receiver isn’t getting enough ‘deviation’ in the modulated signal (the audio on the radio ‘carrier’) to drive the bass correctly. It might not drift enough to lose lock on the signal, but could be enough to degrade the audio. FM receivers need to be tuned to the channel centre frequency in order to correctly demodulate the audio. The bass comes from the largest deviation. It it’s off-centre then it may be seeing less deviation, therefore less bass. This could be temperature related. Only a radio workshop would be able to prove it and fault find though. It should not happen with modern digital tuners.

Does the issue disappear once the car warms up - say on a longer journey? If so it could be component ageing that is causing the ‘drift’. Seasonal changes used to play havoc with the Police comms kit that I used to work on back in the day.

[Themoog2]

Yes the radio does return to normal after driving fo more than an hour. It is sometimes OK as soon as I switch on but only in warmer weather

[Themoog2]

I had a quick listen to the speakers today and the door speakers seemed to be muffled with only the tweeters working properly. The subwoofer was also muffled. When I changed to CD they all worked fine.
The kids reckon it sounds like I'm playing the radio on my phone in the car..
Is there a amplifier anywhere I don't know about that has anything to do with the radio?
As far a it being seasonal, common sense would say there is a connection that is expanding and contracting due to temperature. That doesn't explain the interference from the rear demister tho.

[henrym3]

On the demister make sure the boot lid earth strips are in good nick. Perhaps even remove clean and refit. Pity you didn’t have a cheap aerial to just plug in and confirm or deny the Oe system

[Themoog2]

I'll have a look today but in the meantime I've contacted Cartronics who I sent the bm24 unit to for repair. If it was not faulty then surely diagnostic would have shown that and I shouldn't have had to pay £48..

[Themoog2]

I was in contact with Cartronics and they said it may be the fm tuner inside the bm24 that's at fault. If that's the case then a new unit is required. Surely diagnostic would have picked that up..
I had a look yesterday and there is no obvious damage to any cables etc and the amplifier hidden under the cd changer is not sitting in a pool of water. Stumped.

[henrym3]

I suppose in an ideal world you would be able to swap the bm24 to confirm or eliminate.

[StuBeeDoo]

Surely diagnostic would have picked that up

With any problem, you can't diagnose/trace it until you can replicate it. If the problem is related to temperaure/humidity (you said the problem is winter-related), unless they tested it under very similar conditions to those in which you experience it, it probably wouldn't happen. Remember they will be working in a heated workshop/lab, and you don't get the problem in warmer months.

You've mentioned Cartronics. I've used Carphonics a couple of times to repair BMW units. IMO they do an excellent job, but you need to be very specific with your description of the fault.

[Themoog2]

I took all my tools out of the back the other day so I could load it with something else. After replacing the tools etc the radio has been OK.. Even the rear demister doesn't interfere with it. Odd.