Weird problem: static in the stereo all of a sudden

[Magnesium]

2011 S4, B&O stereo, no mods of any kind on the car. I usually shut off the MMI when I pull into the garage at work because I find the radio auto-start annoying, so yesterday as usual I shut it off and started it again on the ride home. But now there's static on every station. AM, FM, no difference. Used fader and balance to isolate speakers, made no difference, so it's not a speaker problem. And the static is very consistent, doesn't change in significance like when you have real static (i.e. static based on your proximity to the transmitting antenna).

Very strange since I haven't touched anything in the car and it magically developed this problem while sitting in the garage at work for a few hours. Any suggestions on where to start?

[sepheroth86]

A VCDS or OBD11 scan might yield some information.

[Smac770]

But non-radio sources work fine?

Could be the RF signal amp is broken. Or the connection to the rear window glass is broken loose.

https://audi.7zap.com/en/usa/audi+a4...6/0/035-35010/
So the amp R112 (5) and the amp R111 (6), different part revisions depending on vehicle configuration.
You probably have 8K5 035 225 AA on the left D-pillar and probably nothing on the right D-pillar (8K5 035 225 C on the right D-pillar was for the FM3 line in MMI 2G).

Could be an issue with the line from the R112 amp to the radio, or maybe the radio unit broke. Thus start with a scan, see if it points to something specific. But issues with the amp or the window connection would not be unheard of.

[Magnesium]

Thanks guys, great advice. Will start there. Didn't realize and OBD scan would potentially reveal codes for a radio problem, that is pretty nifty. This is the newest car I own.

[sepheroth86]

Thanks guys, great advice. Will start there. Didn't realize and OBD scan would potentially reveal codes for a radio problem, that is pretty nifty. This is the newest car I own.

You need a VCDS, OBD11, or ODIS to properly scan these cars.

A simple code reader will not communicate with all of the modules.

[Smac770]

A generic OBD-II powertrain scanner will just scan the generic OBD-II modes. You need a scan tool that understands the Audi communications structure and queries each installed control module directly for DTCs. VCDS (ross-tech.com), VAG Com Pro (vcpsystem.com), OBDeleven (obdeleven.com), to some extent Carista (caristaapp.com), various Autel tablets. ODIS refers to the actual Audi diag system used by dealerships and shops that subscribe to it; anyone can sign up for it if they want to pay for it, see erwin.audiusa.com.

[Magnesium]

Thanks guys, I have OBD11 and just did the scan. Nada. Couple of intermittent codes for other trivial things but nothing related to the stereo or associated components. I also verified that audio plays cleanly via bluetooth -- static is only present when listening to FM/AM. So it's gotta be an antenna or antenna amp or the connection to the glass (I hope). I will investigate further. Thank you especially @Smac770. Looks like the relevant parts are cheap so even if this becomes a parts-changing expedition it won't be too expensive. I hate parts-changing.

[Smac770]

I can't comment on the quality of the instructions in the video, but it has a good capture of your area of concern. So take it for what you can use from it.

https://youtu.be/1QEm_xxIc0w?t=102

[Magnesium]

So, I pulled the trim off the left D-pillar to access the antenna amp. All wires to the antennas in the rear glass looked fine. I unplugged them from the amp and interestingly, the radio no longer plays audio -- but the static is still there. It's like isolating the stereo so all you hear is the static. So I guess this means that the antennas are functioning and the static is coming from somewhere else. Presumably the amp? (#5 in this schematic: https://audi.7zap.com/en/usa/audi+a4...6/0/035-35010/)

Is there anything else that could introduce the static?

[Smac770]

That it's only on the radio sources, it's most likely an issue in the radio unit itself then.

This is MMI 3G? Unit in the dash above the climate controls says "Audi multimedia" and the controls are below the shifter? MMI uses an optical ring to transfer audio. The J794 (the unit in the dash) sets up the data connections from whatever is supplying the audio information to the amp unit (the amp is a separate unit in B&O, it's integrated into the radio unit without B&O). The radio unit in the left rear manages only tuner sources (AM/FM/Sirius) (for B&O, it's also the amp for non-B&O). If you're getting noise whenever selecting those sources, but not from any other sources (CD, AMI, Bluetooth) or other functions (nav instructions, handsfree talk), then the issue is with the audio data coming from the radio unit. Static for a radio tuner, one would normally presume an antenna issue. But it could be the radio itself has trashed. There's no reason to assume an issue with the amp, unless the issue was present no matter what audio source you selected.

Given your test, it's most likely a circuit failure inside the radio unit introducing noise into the signal path. Similar to the amp in my PC speaker sub after a breaker trip. It works fine, but there's a baseline hum now. I can hear it in the transformer on the circuit board; it just carries on the signal to the sub and is even louder there. Likely a defect in the power supply control IC. Guess the power trip just took it out. Probably some circuit component in the radio unit died. Maybe an IC, maybe a cap.

[Magnesium]

Thanks, interesting. Appreciate the guidance. Yes, 3G MMI. I just pulled the radio amp out of the left side of the trunk. The part number sticker is very helpfully placed on the one side of the unit that you can't see without removing it. Terrific. Anyway, here are some pics just for kicks. There are a hundred of these for sale on ebay but they're surprisingly pricey. What are the chances a local electronics specialist could just repair my unit now that I've got it out of the car? This is the item that you think is probably the culprit?

[HowdyQuattro]

Is your battery healthy and not end-of-life in terms of age? Radio static/hiss was one of the leading indicators of my battery failure a few years ago if I recall... perhaps the antennae components are sensitive to power quality.

[Magnesium]

Interesting suggestion, but I doubt it. I will put my multimeter on the battery but it is new as of a month ago, put it in right when I bought it.

[Smac770]

The J525 amp has the fins on it, that's what's in your pics. That is not the radio. The radio is the rectangular box below it with the large quad-plug and the FAKRA cables on it.

[rsfpc05]

Ironic timing of this post, drove to work on Monday and everything was fine. Leave to head home and I hear this static noise on all stations but not on SD media. Haven’t driven the car since then to see if it’s still there.

[Magnesium]

Ok, update time. I had a drive ahead of me over the weekend and decided to reinstall the amp (the thing in the pics above) since it takes all of five minutes. Got in the car, turned on the radio, and....no more static. Been a few days now and the problem is still gone. I don't begin to understand how unplugging that amp and plugging it back in could have made the problem go away, but it did. For now.

[Smac770]

It's like the disk arrays at the old job. Disk bad light is on, unplug it / replug it, and now it's good disk again.