Radio/Stereo: - V70 SC900 intermittent FM signal

Luxobarge · Sep 20th, 2019, 21:32

Hi all - 1997 V70 with a standard SC900 stereo system.

Fault is that occasionally I lose sound on FM. The radio head unit is still turned on and live (normal display etc.) I just lose the sound. It only happens on FM, if I change to AM or CD it works fine. Sometimes if I thump the console it comes back, so definitely seems like a dodgy connection somewhere.

It's definitely not a problem with the main head unit, as I replaced this recently with a good working one and the problem remains.

It's only on FM, so I think this must have an FM antenna amplifier somewhere - can anyone tell me if this is so and where it is? Any other devices or connections that are unique to FM only, that I should look at, and where are they? It's not the connection on the co-ax antenna cable going into the head unit, as I can play the radio while it's hanging out of the dash and fiddling with this cable (or any of the others come to that) doesn't reproduce the fault.

It works most of the time, but go over a bump and it'll go silent for a while, or sometimes it doesn't come on when the ignition is first switched on, (although the head unit comes alive) and will only give sound after a few minutes. Might be a dry solder joint somewhere (which I can probably fix) but where?

Any help much appreciated as ever!

Clan · Sep 21st, 2019, 09:11

Quote:

Originally Posted by Luxobarge

Hi all - 1997 V70 with a standard SC900 stereo system.

Fault is that occasionally I lose sound on FM. The radio head unit is still turned on and live (normal display etc.) I just lose the sound. It only happens on FM, if I change to AM or CD it works fine. Sometimes if I thump the console it comes back, so definitely seems like a dodgy connection somewhere.

It's definitely not a problem with the main head unit, as I replaced this recently with a good working one and the problem remains.

It's only on FM, so I think this must have an FM antenna amplifier somewhere - can anyone tell me if this is so and where it is? Any other devices or connections that are unique to FM only, that I should look at, and where are they? It's not the connection on the co-ax antenna cable going into the head unit, as I can play the radio while it's hanging out of the dash and fiddling with this cable (or any of the others come to that) doesn't reproduce the fault.

It works most of the time, but go over a bump and it'll go silent for a while, or sometimes it doesn't come on when the ignition is first switched on, (although the head unit comes alive) and will only give sound after a few minutes. Might be a dry solder joint somewhere (which I can probably fix) but where?

Any help much appreciated as ever!

Has this happened since someone had the rear bumper off ? There is a FM antenna on the right hand side and the black wire goes through into the right hand wheel well with a plug . The two antennas work together to obtain the strongest signal .

Luxobarge · Sep 21st, 2019, 12:59

Hi Clan,

No, bumper's never been off. Are you sure the antenna in the bumper applies to phase 1 cars? I thought this was only phase 2, but very much stand to be corrected.

It's not an issue of signal strength, when it goes there is absolute silence, no static/crackling etc. just absolutely nothing.

Clan · Sep 21st, 2019, 14:34

Quote:

Originally Posted by Luxobarge

Hi Clan,

No, bumper's never been off. Are you sure the antenna in the bumper applies to phase 1 cars? I thought this was only phase 2, but very much stand to be corrected.

It's not an issue of signal strength, when it goes there is absolute silence, no static/crackling etc. just absolutely nothing.

tricky one . yes they original V70/C70 had this antenna on the right inner side of the rear bumper ..

Luxobarge · Sep 21st, 2019, 15:08

OK cool, that's another place to look, I'll check that out. Certainly the side screen antenna on the right side glass window isn't connected.

Oddly, I did start looking at the left side glass window antenna today, I had the radio on in the car while I worked (it decided to work at this point) and wanted to check connection quality, so I removed some of the boot trim pieces and first disconnected the power to the antenna amplifier that sits behind the side trim (I discovered where it was!) and then popped off the actual antenna connections to the glass. It made no difference to the radio whatsoever! I find this strange, maybe my left side antenna is not connected at all, and there's a fault with the right side one, whereby I get no signal at all when it fails. I shall do some more digging here and see what I can discover.

Anybody know where the two antenna feeds join up?

Cheers!

SwissXC90 · Sep 21st, 2019, 16:23

Quote:

Originally Posted by Luxobarge

first disconnected the power to the antenna amplifier that sits behind the side trim (I discovered where it was!) and then popped off the actual antenna connections to the glass. It made no difference to the radio whatsoever! I find this strange,

Not strange at all, due to the FM radio's AGC (automatic gain control)

The antenna amplifier does amplify the signal, but also signal goes through when the amplifier is not powered. And it may be enough non-amplified signal for you at your location that you don't need an antenna amplifier on the station you are tuned to.

To test the antenna amplifier, you need to tune to a station that is so weak that you can hear hiss and noise under normal conditions.
Then you can disconnect the amplifier, and the hiss and noise should increase as the wanted signal decreases.

Alternatively, disconnect the amplifier, then tune to a weak station.
Once the station is found with hiss and noise, reconnect the antenna amplifier.
Does the hiss and noise reduce due to the signal being stronger? If so, the amplifier is working.

Luxobarge · Sep 21st, 2019, 20:37

Hi SwissXC90, thanks for that - understood. However, I also disconnected the actual antenna itself in the window, and no change. I'm guessing that at this point the other antenna (in the bumper) was enough to give a good signal to the radio, it was indeed a major BBC station (Radio 2) so quite strong. I'm planning to find the connections for the bumper antenna, unplug it so that I only have one antenna operational and then do the procedure you outline for each antenna individually to prove what's working and what isn't.

Cheers!

SwissXC90 · Sep 22nd, 2019, 09:09

Quote:

Originally Posted by Luxobarge

Hi SwissXC90, thanks for that - understood. However, I also disconnected the actual antenna itself in the window, and no change. I'm guessing that at this point the other antenna (in the bumper) was enough to give a good signal to the radio, it was indeed a major BBC station (Radio 2) so quite strong. I'm planning to find the connections for the bumper antenna, unplug it so that I only have one antenna operational and then do the procedure you outline for each antenna individually to prove what's working and what isn't.

You will likely find that you can pick up some radio stations even when you have no antenna connected to the radio at all.

This is why you must first identify a weak station down in the noise to do your tests.

Anything else is pointless

Luxobarge · Sep 28th, 2019, 11:38

Quote:

Originally Posted by Clan

yes they original V70/C70 had this antenna on the right inner side of the rear bumper ..

OK, so I had some time to look at this again today. I've had all the interior trim out at the back of the car, and on the right side (driver's side) I cannot for the life of me see anything that could be a bumper antenna, no wires at all go through the rear of the car at the bottom, or anywhere near it, no antenna amplifier, no co-ax cable, nothing. So while I still stand to be corrected, it very much looks as if my car doesn't have an antenna in the rear bumper. If you still think it does, can you tell me exactly where to find evidence of it, i.e. where the wires are, where the amplifier is? Cheers!

So while in there I spent some more time investigating the antenna in the window on the left side. I tuned to a weak station and it got weaker when I pulled the antenna connectors off, and weaker still when I pulled the co-ax cable out of the amplifier, so that's all as it should be. However at no point could I replicate the problem of suddenly losing all sound. It's very frustrating that the problem is so intermittent, as we all know it's very difficult to diagnose a problem when the symptom isn't present!

I did find that the torx screw holding the antenna amplifier to the car body was loose, so tightened that up of course.

Only thing to note is that the fault is often there when I first turn on the ignition. Today this happened, once the radio has come on and the display is on, sound should come almost immediately, but today it didn't. I thumped the side of the console with the heel of my hand and it started working. This has all the hallmarks of a dodgy connection somewhere in the central console area, so after I'd finished at the rear of the car I slid the radio back out and had a thorough fiddle around with all the cable connectors and harnesses near the radio, and found absolutely nothing - the radio was playing just fine the whole time. If I'd got anywhere near the fault I'd have expected it to lose sound at least for a moment, but it seemed as solid as a rock.

Still perplexed by this one, we'll see how it goes when I next drive the car around, but I'm not confident that the loose antenna mounting screw will have fixed it - we'll see. I'll update again either way.

Cheers!

SwissXC90 · Sep 28th, 2019, 11:41

A loose antenna amp mounting screw will really affect AM performance, as AM needs a really good ground connection.

Much less effect on FM

Sep 20th, 2019, 21:32	#1
Luxobarge Premier Member Last Online: Today 22:43 Join Date: Jan 2011 Location: Horne (Nr. Horley)	V70 SC900 intermittent FM signal Hi all - 1997 V70 with a standard SC900 stereo system. Fault is that occasionally I lose sound on FM. The radio head unit is still turned on and live (normal display etc.) I just lose the sound. It only happens on FM, if I change to AM or CD it works fine. Sometimes if I thump the console it comes back, so definitely seems like a dodgy connection somewhere. It's definitely not a problem with the main head unit, as I replaced this recently with a good working one and the problem remains. It's only on FM, so I think this must have an FM antenna amplifier somewhere - can anyone tell me if this is so and where it is? Any other devices or connections that are unique to FM only, that I should look at, and where are they? It's not the connection on the co-ax antenna cable going into the head unit, as I can play the radio while it's hanging out of the dash and fiddling with this cable (or any of the others come to that) doesn't reproduce the fault. It works most of the time, but go over a bump and it'll go silent for a while, or sometimes it doesn't come on when the ignition is first switched on, (although the head unit comes alive) and will only give sound after a few minutes. Might be a dry solder joint somewhere (which I can probably fix) but where? Any help much appreciated as ever! __________________ Some people are like Slinkies, they serve no useful purpose but they still bring a smile to your face when you push them downstairs.

Sep 21st, 2019, 12:59	#3
Luxobarge Premier Member Last Online: Today 22:43 Join Date: Jan 2011 Location: Horne (Nr. Horley)	Hi Clan, No, bumper's never been off. Are you sure the antenna in the bumper applies to phase 1 cars? I thought this was only phase 2, but very much stand to be corrected. It's not an issue of signal strength, when it goes there is absolute silence, no static/crackling etc. just absolutely nothing. __________________ Some people are like Slinkies, they serve no useful purpose but they still bring a smile to your face when you push them downstairs.

Sep 21st, 2019, 15:08	#5
Luxobarge Premier Member Last Online: Today 22:43 Join Date: Jan 2011 Location: Horne (Nr. Horley)	OK cool, that's another place to look, I'll check that out. Certainly the side screen antenna on the right side glass window isn't connected. Oddly, I did start looking at the left side glass window antenna today, I had the radio on in the car while I worked (it decided to work at this point) and wanted to check connection quality, so I removed some of the boot trim pieces and first disconnected the power to the antenna amplifier that sits behind the side trim (I discovered where it was!) and then popped off the actual antenna connections to the glass. It made no difference to the radio whatsoever! I find this strange, maybe my left side antenna is not connected at all, and there's a fault with the right side one, whereby I get no signal at all when it fails. I shall do some more digging here and see what I can discover. Anybody know where the two antenna feeds join up? Cheers! __________________ Some people are like Slinkies, they serve no useful purpose but they still bring a smile to your face when you push them downstairs.

Sep 21st, 2019, 20:37	#7
Luxobarge Premier Member Last Online: Today 22:43 Join Date: Jan 2011 Location: Horne (Nr. Horley)	Hi SwissXC90, thanks for that - understood. However, I also disconnected the actual antenna itself in the window, and no change. I'm guessing that at this point the other antenna (in the bumper) was enough to give a good signal to the radio, it was indeed a major BBC station (Radio 2) so quite strong. I'm planning to find the connections for the bumper antenna, unplug it so that I only have one antenna operational and then do the procedure you outline for each antenna individually to prove what's working and what isn't. Cheers! __________________ Some people are like Slinkies, they serve no useful purpose but they still bring a smile to your face when you push them downstairs.

Sep 28th, 2019, 11:41	#10
SwissXC90 Premier Member Last Online: Mar 20th, 2024 18:26 Join Date: Jan 2016 Location: Cross Country	A loose antenna amp mounting screw will really affect AM performance, as AM needs a really good ground connection. Much less effect on FM __________________ XC90 R-Design MY2009, Black Sapphire Metallic. HP-Sound, RSE, Nav, Tel, ParkingCam, BLIS, ParkingHeater, RestHeat, Removable Towbar, Summer: CRATUS 20x8 on Pirelli Scorpion Zeros 255/45, Winter: NEPTUNE 17x7 on Continental WinterContact 4x4 235/65.

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