Radio signal broken (impedance converter 1/2)

[zokiopp]

Hello people

Im an owner of an a5 2013 b8.5 sportback

Im looking for some help fixing my radio. It just emits static noise and no signal at all whatsoever. It happened after i turned on rear defog day after installing rear window tint. Fault codes in infotainment are:
1. 02981 Connection between the impedance converter 1 and the radio
- open circuit
- permanent

2. 02982 Connection between the impedance converter 2,and the radio
- open circuit
- permanent

I changed the antenna boosters that are located in the rear trim with some used ones from another audi from junkyard, deleted the codes in autocom but nothing changed. Codes are back again.

Thank you in advance

[Smac770]

What's the unit in the dash above the climate controls say? Audi chorus, Audi concert, Audi symphony, or Audi multimedia? Is this a DAB vehicle? What radio band is static? FM, AM, and/or DAB?

For the B8 sportback, the aerials amplifiers are:

R24 - top of rear glass, left
AM/FM1 to radio
if equipped, TV1 to tv tuner

R111 - bottom of rear glass, left
FM2 to radio
FZV (central locking) to J393

R112 - top of rear glass, right
if equipped, DAB to radio
if equipped, TV2 to tv tuner

R113 - bottom of rear glass, right
if equipped, TV3 to tv tuner

So I assume the error codes are talking about the aerial amps along the left side, top and bottom, for FM1 and FM2? If you unplug those FAKRAs at the radio, what do you measure for resistance from center pin to the surround pin? I got 101 kΩ and 71 kΩ for my two connections, but I have MMI 2G. That uses a different FM tuning philosophy than MMI 3G. Not sure what the CAN radios use. But if you measure yours, you'll probably get no measurement.

If you unplug the actual window leads connector from the R24 and R111 and measure the resistance between pins 1 and 2 of each, what do you measure? Is it again no measurement / open circuit? Then something is wrong with the leads connection to the glass aerial or with the aerial in the glass itself.

Is this metallic tint?

[zokiopp]

What's the unit in the dash above the climate controls say? Audi chorus, Audi concert, Audi symphony, or Audi multimedia? Is this a DAB vehicle? What radio band is static? FM, AM, and/or DAB?

For the B8 sportback, the aerials amplifiers are:

R24 - top of rear glass, left
AM/FM1 to radio
if equipped, TV1 to tv tuner

R111 - bottom of rear glass, left
FM2 to radio
FZV (central locking) to J393

R112 - top of rear glass, right
if equipped, DAB to radio
if equipped, TV2 to tv tuner

R113 - bottom of rear glass, right
if equipped, TV3 to tv tuner

So I assume the error codes are talking about the aerial amps along the left side, top and bottom, for FM1 and FM2? If you unplug those FAKRAs at the radio, what do you measure for resistance from center pin to the surround pin? I got 101 kΩ and 71 kΩ for my two connections, but I have MMI 2G. That uses a different FM tuning philosophy than MMI 3G. Not sure what the CAN radios use. But if you measure yours, you'll probably get no measurement.

If you unplug the actual window leads connector from the R24 and R111 and measure the resistance between pins 1 and 2 of each, what do you measure? Is it again no measurement / open circuit? Then something is wrong with the leads connection to the glass aerial or with the aerial in the glass itself.

Is this metallic tint?

I have audi multimedia (Bnav EU P056 D1)with central console with navigation which uses the shark fin antenna i think. I have no tv tuner i suppose eu cars dont have dab. I guess the errors are the two radio boosters ( one inside the trim on the left side rear hatchback windeo and one below it) . Both are part no: 8T8 035 225 and 8T8 035 225c ( this has one grey and one white connector which goes to the radio and i wish i know where the grey comes from. An electrician was measuring the resistances and said everything is okay but im waiting him to reply me with exact numbers so i can explain to you. Theres no fm or am station available at all. I remember that the electrician put copper wire on the white connector that comes from the radio to the 225c module and we got some signal from a nearby station. When he tried bridging it to the window antenna connector, it killed the signal right away. I have installed black tint but we thought that there may be metalic shards inside it and i removed the tint and still, nothing changed. The defroster is working, the tinting installation uses a lot of soapy water splashing which i think caused the issue somehow. The issue came after using defroster with freshly installed tint(2 days). I will wait for the electrician to give me the measures that he got and will include in next reply

Thank you alot for helping me.

[Smac770]

DAB tuning is optional, and certainly a Europe thing, particularly UK. Same for tv tuner.

If you are QV0 or QV3, then the upper left is 8T8 035 225 and the lower left is 8T8 035 225 C. Yes, this is easy enough to see in the parts catalog.

The error code is clear, open circuit. The radio is in the back left corner, maybe it got wet.

You can see the double FAKRA on the back of it. Unplug it and confirm the resistance measurement for each FAKRA line. Should be simple enough to validate which is AM/FM1 from R24 and which is FM2 from R111.

Maybe the FAKRA lines got trashed. If you can measure resistance on the FAKRA port on the aerial amp, but not on the FAKRA port on the cable when the cable is plugged into the aerial amp, would seem the cable is shot.

[zokiopp]

Fakra lines are measured and they work. We measured the window antenna green wire from smaller amp. (R24) that has two wires with the other window antenna plug to other amp which has only one wire (r111) and they are good. I took out the tint and its the same thing

[zokiopp]

When we bridge the fakra line from the radio at the end with a copper wire, we get some radio stations signal. When we bridge the cooper wire with the window antenna on the glass connector that connects to the amp, it kills the frequency. Can you tell me where the grey connector goes from the bigger amp and whats its purpose? Can it be the problem?

[Smac770]

The upper left amp is the R24 and provides AM and FM1 combined over a single FAKRA line. On the 3-pin connector to the aerial leads, it uses pins 1 and 2. It doesn't explain 1 vs 2, just that each connects to the R93 aerial. Looks like pin 1 is the black wire and pin 2 is the green wire?

The lower left amp is the R111 and provides the FM2 FAKRA to the radio unit and the FZV central locking FAKRA to the J393. Look at the J393 in the right rear, the FAKRA cable going to it along with the 17-pins and 32-pins on it. Does your key fob work? On the 3-pin connector to the aerial leads, pin 1 is to the R11 aerial for FM2 and pin 2 is to the R47 aerial for FZV.

What did you measure as the resistance between the center pin and the surround for AM/FM1 and for FM2 cables at the radio? If you measured a resistance, then clearly it's not an open circuit. So the radio would seem to be in error. Or maybe you measured something, but it was too high.

If there's only one wire at the aerial connector plugged into R111, what pin is that wire on? Because the B8 A5 Communications workshop manual says there's a wire on 1 (FM2) and 2 (FZV).

"bridge the fakra line from the radio at the end with a copper wire" I have no visual of what you are trying to say there. You mean replace the FAKRA cable with a normal wire from the radio FAKRA plug to the aerial amp FAKRA plug? Which radio plug, which aerial amp? The AM/FM1 to the upper R24, or the FM2 to the lower R111? If you skip the amp, you'll get nothing; that's expected. Still sounds like the FAKRA lines are "FAK'd". Do you have another FAKRA cable to try?

What gray connector. Gray FAKRA connector? I don't know smaller and larger, I know the upper one and the lower one. I'm working from documentation, not a car sitting in front of me.

[zokiopp]

The resistance is measured between the fakra ends and it was like around 50 oms that probably means that they are good. The r111 has only 1 black wire on the middle pin coming from the window aerial to the r111. R24 three pin connector has 2 wires ( green and black). Btw The cooper wire i used as a simple antenna just to get some signal. I attached it to the center pin of the FAKRA thats coming to the r111 and it got some radio station signal bypassing the r111.

[Smac770]

I decided we needed a diagram, as something seems to be getting lost "in translation". Weekend was too busy to get around to it though. But here we go:

Audi 8T sportback aerials.jpg

So the radio has a dual FAKRA connector, with one cable going to R24 for the AM/FM1 signal and one cable going to the R111 for the FM2 signal. When you talk about "I put a wire into the center pin of the FAKRA connector", which one? The one for AM/FM1 at the R24, or the one for FM2 at the R111? Because my wonder is if there's a problem only on one of the FM paths, why isn't the radio simply using the other FM path for the time being?

MMI 3G radio tuner block diagram is on SSP 435 page 32. The diagnosis system is on page 40. But your error message seems to be about the FAKRA connection to the aerial amp, not the leads connection to the window aerial.

I've seen pics of the R111 unit (p/n rev C), and they do show just a single wire. But it's hard to tell if that wire is on pin 1 or pin 2. Could be the FZV aerial is built into the amp and doesn't need an external connection?

The trunk based sedan and coupe use a different rear aerials config (upper left R112 and upper right R111) than do the tailgate based avant and sportback (R24 + R111 + R112 + R113). But my wagon is MMI 2G, so the amp layout system is quite different from MMI 3G. But I seem to have an actual wire to glass for the FZV. So can't explain why you don't have two wires on your R111 to the glass.

[zokiopp]

I have question: why did i started getting some radio signal after i released and tightened the bolt that holds the r24 on the side hatch? Is the screw used as a ground maybe?

[zokiopp]

I plugged the copper wire on the fakra that goes to the R111 btw

[Smac770]

I could certainly believe the amp unit grounds to the chassis, but I don't know that it does that for sure. Never took one apart to see exactly what's going on inside. Could be it needs the chassis reference to set the ground plane.

Do you get the same result if you unplug the white FAKRA from R24 and put a "wire aerial" directly into it? Ie, why isn't FM1 appearing to work either. It could be MMI 3G diversity tuning requires both inputs to tune a signal. I can't test that, as MMI 2G using a different diversity philosophy. But that's the part I find odd.

On the R111, so if you put the FAKRA back and put your wire aerial on the pin 1, does it also work? Or does having the amp inline mess things up. Did you do something like dynamat so the amps are not sitting on the metal as originally?

Is the wire on the aerial connector to the R111 on pin 1 or pin 2. The few pics I could find were only from the side and so indeterminate. Is there a loop on the plug from pin 2 to pin 3? Could be the key fob needs only that little loop to be picked up.

[zokiopp]

If i put a wire aerial, on the window antenna pin 2 on the r111(only one black wire going to the middle pin), signal is killed. Also, i noticed a low range from my remote key. I used to unlock the car from 100 meters away and now is struggling to open even when im like 10 meters away. Theres loop between pin 1 and 2. We measured the black wire to the ground and has 0 voltage. Can you give me a diagram of the rear windshield to see how is the wiring of it? There must be some voltage so the amps to work properly. Theres no power.

[Smac770]

Ok, so the wiring for the R111 is aerial wire from glass goes to pin 2, but then there's a jumper on the connector from pin 2 to pin 1. So the connection for FM2 on pin 1 and for FZV on pin 2 are just jumpered together. Most likely there's two amp circuits inside, both fed the same input signal, but the amps are tailored to the specific frequency range and then sent out to the two relevant devices. You can look at your J393 BCM2 to see what frequency your key fob is using. Will be 315 MHz, 433 MHz, or 868 MHz. But FM is just 87-106 MHz. RF is AC, not DC. And a meter is not likely to work in those frequency ranges (home meters AC tend to be only up to 400 Hz, and focused on 50/60 Hz).

I have no idea if the aerial amps look for phantom DC power sent along the FAKRA connectors, or are just passive induction coil setup. But everything seems to point to them having some manner of power injection via the FAKRA cable. This would be why the ground to chassis is important. But you should be able to measure some DC voltage on the FAKRA connection if it is phantom powered. But for the R111, are both the radio and the J393 sending phantom power, or is only the radio, or is it only the J393? I have no information on these specifics. And since I don't have MMI 3G, it's not something I can go check on my car. But maybe the amp isn't getting the phantom power it needs to switch on.

I still find it odd that with the R111 disconnected, that your AM and FM is still shot, since AM has nothing to do with R111. It's almost like R24 isn't doing anything either.

Audi doesn't clarify the physical positioning / connections of the aerials in the glass. Hell, I can only find a single pic of the 8T sportback rear glass to even look at.