FM radio is silent or comes in poorly

[erikv11]

Seems likely there would be multiple ways these fail, with slightly different symptoms, yes. Too bad the steering controls don't give a workaround for you, was worth a try!

[EngineeringBloke]

The HU-650 head unit outputs 10 volts to the antenna amplifier. (Its a Ford thing, apparently.)

I put in an after-market Pioneer audiophile head unit, a 5 way Audison amplifier with after-market Audio Frog tweeters, mid-range run active (using the Pioneer electronic crossover that provide 4 different frequencies ranges) and a sub-woofer in the trunk.

I had put the '12 volts' headunit raise antenna output on the line to the antenna amplifier but reception was poor when the alternator was doing 14 volts. When stopped and the car was not running, the battery was doing 12 volts and the reception was much better.

I then added a large 50 ohm 10 watt resistor in line between my Pioneer and the antenna amp to further reduce the voltage. This restored FM and improved AM, too. I plan to replace it with a 10 volt voltage regulator, as I think that will be better but have not done this yet. This line only needs to provide low current, perhaps 0.1 to 0.5 amps at most, maybe much less.

If your head unit is having a problem providing 10 volts, then switching the amplifier would not fix your issue. A volt meter check at the head unit or at the antenna amplifier may be worth doing.

Antenna amp Service Note

Also, there was an issue with the FM signal input on the antenna amplifier from the antenna, unrelated to the 10 volt supply. There was a service note that specified a small brass strip to be inserted on that input. I'm not sure how that improved things, and the fact that your issue is intermittent makes it more likely that there is an issue with 10 volt generation or the wire providing that to the antenna amp.

[FMradio]

Same here. It's fair to say that 15 yrs is the life expectancy of a majority of the P2 Volvo parts whatever it may be. I think there's a video on someone adding a heatsink to a chip in order to stop it from overheating. Otherwise you are suppose to replace the unit with a used one, and what, have it last for 5 ish years?

I think you guys are right that the head unit is the problem. I've also seen a YouTube comment where somebody said the stock head unit is junk because the FM radio fails on it.
I might replace it with an aftermarket one, so I don't have to bother with buying a used one at the junkyard which might fail on me. They aren't even that cheap, like $20-30 for a used head unit at the local u-pull-it. Definitely not worth it unless somebody has electronics repair knowledge. I love the design of the stock head unit, but the FM radio problem is a dealbreaker! On the other hand, there's a chance that the junkyard one Iasts for many years, but it's not worth the price and risk to me.

If I install an aftermarket unit and find out it is working, I will update the thread. Also I find it weird how on this car you have to be careful to unplug the battery before removing the climate control unit and wait for 30 minutes, else you'll trigger an SRS light that must be reset with a mechanic's scan tool or the dealership. Also, before reconnecting the battery, you're supposed to put the key in position 2 and do a few other things (maybe put on the headlights) in order to avoid burning out the temperature sensor in the climate controls. A few strange things to worry about when working on this car.

[FMradio]

I found out my AM radio isn't great either. Compared to my Buick, only a few stations come in, and some come in poorly. Buick receives all AM stations and has perfect reception. That makes me wonder if my antenna amplifier is defective, head unit is defective, or if it is both antenna amplifier and head unit. I know that there was a TSB for the AM radio on this car where they installed a copper piece onto the antenna amplifier to fix poor AM reception. Though, this TSB was released in 2003 and my car is a 2006. Presumably they had fixed the problem by 2006, so maybe my antenna amplifier is bad or just a loose connection.
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[iamhives]

Aren't AM and FM different aerials

[FMradio]

The HU-650 head unit outputs 10 volts to the antenna amplifier. (Its a Ford thing, apparently.)

I put in an after-market Pioneer audiophile head unit, a 5 way Audison amplifier with after-market Audio Frog tweeters, mid-range run active (using the Pioneer electronic crossover that provide 4 different frequencies ranges) and a sub-woofer in the trunk.

I had put the '12 volts' headunit raise antenna output on the line to the antenna amplifier but reception was poor when the alternator was doing 14 volts. When stopped and the car was not running, the battery was doing 12 volts and the reception was much better.

I then added a large 50 ohm 10 watt resistor in line between my Pioneer and the antenna amp to further reduce the voltage. This restored FM and improved AM, too. I plan to replace it with a 10 volt voltage regulator, as I think that will be better but have not done this yet. This line only needs to provide low current, perhaps 0.1 to 0.5 amps at most, maybe much less.

If your head unit is having a problem providing 10 volts, then switching the amplifier would not fix your issue. A volt meter check at the head unit or at the antenna amplifier may be worth doing.

Antenna amp Service Note

Also, there was an issue with the FM signal input on the antenna amplifier from the antenna, unrelated to the 10 volt supply. There was a service note that specified a small brass strip to be inserted on that input. I'm not sure how that improved things, and the fact that your issue is intermittent makes it more likely that there is an issue with 10 volt generation or the wire providing that to the antenna amp.

Wow, you've done a lot of work. I'm sorry I missed your post, I didn't notice it. Thanks for all the knowledge! Your radio and speaker upgrade sounds like it took a lot of work (no pun intended). It must sound great! I would like to try to diagnose my car's problem. I'll get a multi-meter some day and test the 10 volts. Thanks for telling me about it. Hopefully the antenna amplifier is the issue, not the head unit's 10v supply, or some internal failure inside the head unit, because it would be so simple to swap the antenna amp with a working one.

If my head unit is broken, I would love to replace it with another stock unit as I like them and it would be fairly simple, but I'm worried if I pick up a used head unit at the auto junkyard, I will pick up another broken one or one with a limited lifespan. The best bet may be picking up a refurb on eBay, but I hope they won't fail eventually and it's a bit pricey.

Is DIY installing an aftermarket head unit difficult? I don't need to install the speaker amplifier, and my car doesn't come with the factory amplifier so I don't have to worry about that. I understand that the hardest part of installing car radios in most cars is wiring up the harness, but you mentioned that on this Volvo we also need to provide a 10v power source for the factory antenna amp. And one this car, the 10v is provided by the stock head unit which we took away, so we need another source of 10v power. Is it difficult to do that? (also I may lose steering wheel controls unless I buy a special adapter box)

I also thought about upgrading my head unit hu-650 to an 850, but I heard that the 850 has problems too. (I saw a YouTube video where somebody was trying to fix a design flaw where 2 circuitboard components got so hot they charred the board, and after fixing that issue it eventually developed other issues)

[FMradio]

Aren't AM and FM different aerials

I'm not sure. I read somewhere that AM and FM both use the same antenna, which is the defroster grid on the back window, plus a second diversity antenna located in the bumper. I'm not sure if the diversity antenna is standard on all Volvos or if it was an option, though. (this theory would make sense since Volvo had a service bulletin for fixing AM reception by adding a copper strip to the antenna amplifier that is connected to the antennas)

[FMradio]

Update, an independent volvo mechanic checked our radio and says the fault is internal to the radio unit. So in the future, I'd like to replace it with an aftermarket because I don't want to add another stock radio and have it fail too. Hopefully will find an already-made wiring harness in a car at the U-pull it yard to save me that work. But I think that people would probably take their aftermarket radio out before junking their cars. Also have to figure out how to provide 10v power to the antenna amplifier because my understanding is that the stock radio unit provides 10v.

[FMradio]

I wonder if the radio really has an internal flaw and the flaw is not providing the power needed for the antenna amplifier in the back of the car. If I recall correctly, the radio provides 10v to the antenna amplifier. Is there a way for me to make a 10v power supply and replace the head unit's power, and make the antenna amplifier work? That is if this is a power issue. Sometimes my radio works great then it starts to cut out and become very quiet, or goes totally silent. It doesn't really make static noises like I would expect a bad signal to cause but perhaps that is a feature of the radio, I dunno? Maybe I'll find a way to disconnect the power from the antenna amp and see how the radio reacts. Will FM Radio still be totally silent? Or will it make a static noise. Ideally I'd find a time when the FM radio is definitely playing sound, then unplug the power from the antenna amp while it is working and see if the radio goes silent or goes to static. If it goes silent, then I would presume that when the head unit doesn't play FM radio, then it's not sending power to the antenna amplifier. If it goes to static, there is some issue that prevents the FM signal from being converted to sound. (not sure if that's the correct word) Because AM works, and CD works just fine all the time, even when FM doesn't work. However the AM reception in this car is not as good as my Buick, which may indicate that the antenna amp is not working properly or it is just a bad antenna design for AM.

I will try to find when the FM is playing, if I can tune into more AM stations. That will lend further support to theory that the antenna amp is not receiving power, because that should worsen both FM and AM reception at the same time right? Unless AM radio doesn't need an amplifier.

[packetfire]

The intermittent nature of the problem tells us that there is a bad connection.

Forget the antenna - it seems good - if the antenna were the issue, you'd hear static (just like between stations), not silence.

Basic radio electronics work like this -- The audio preamp receives the signal from the AM tuner, or from the FM tuner, or from the cassette player. From the preamp, the then line level audio signal is routed through the tone controls and then the volume, balance, fader control. As only FM audio is affected, you have a bad connection between the FM tuner section and the audio preamp/EQ section of the radio.

You need an electronics guy, not a mechanic. Often, one can see the bad connection, the solder joints on cables and such are bad when they look bad, so visual inspection can be all that is needed.

I have a perfectly good HU-613 from my 2004 v70 you can buy cheap, but I swapped mine out because I demand a stereo that violates the Nuclear Test Ban Treaty, so I wired up the antenna to get power to the antenna amp (up in the roof above the rear-window antenna on the driver's side, just behind the plastic adjacent to the headliner), and I also installed a cute little Arduino interface to make the steering wheel controls work with my after-market stereo. Volvo's speakers are pretty decent, but their audio gear is wimpy.