Shamoye Lewis

something is shorting the Head, you mentioned before there is a device between the head and screen on the LVDS cable remove it just unplug it from the head you don't need to connect the screen back it will just be temporarily blank, just have the HEAD, power/can harness and optical connect and see what happens.... didn't get a chance to do the test I said funeral came up.... if the head is dead just buy another on, fixing/eval is unnecessary money, I never seen a drink spill kill the head only the E380, could be all coincidental...

ltooz_a6_a8_q7

spilled drink on the control panel.
<a href="https://www.audiworld.com/forums/a8-s8-d3-platform-discussion-60/mmi-acting-up-experts-please-help-2867744/">Check the 5A communication box in the trunk</a>.
I would remove the optical cable from the head unit, look inside the connector to see if the red led is blinking, if it's blinking, it should be working. Unplug all the other ones to see if the cable is blinking and the device is blinking also.

Cheers,

Louis

mishar

+1

haggisuk

Spilled coffee on mmi could indeed kill the control head, the control head is the source of power to the mmi control panel.

But like i said before i would like to see the the aftermarket box removed and the control head wired as per factory and that means the optical loop back to original as well and then show us a new vcds scan along with the optical loop test also so we can see if the control head is indeed dead.

The flashing diode test that was mentioned is a good test to see what is working also but requires cycling of the ignition off and on to get some modules to start flashing as they time out and stop flashing after a few seconds on an open loop.

ltooz_a6_a8_q7

Inside optical bus unit, it does have LEDS and for any reasons, the LEDS are blown, then you won't see the red LED blinking and we think the whole head unit is dead but it may not. If it were me, after checking out that the head unit optical connector red LED doesn't blink, I would unsolder the MOST bus unit, these are through holes so they're easy, swap with a working connector from a cheap unit to see if it works. Easy way is to buy a used one without knowing if it works and CP problems?

I don't have a problem with the MOST, but if I had, I would tear up the connector unit and see what kind of LEDs they used and replace them. All circuits are well protected with overloading voltages and shorts, especially with Audi Engineering, the board may not be bad, if you have 12V in the head unit and stays, there's no short, it's the in/out circuits.



looking at the design of the box - I don't know how control panel can kill the Head Unit Main board - Unless they use the same power bus which I doubt - The only thing that shared is the OPTICAL bus.



Found it... the transceiver.


<a href="http://www.ece.mtu.edu/labs/EElabs/EE2304/EE2304_website_2008/Signal%20Processing%20Labs/ee2303_fiberoptic_transciever.pdf" target="_blank">How to build fiberoptic_transceiver</a> - PhotoLED is the one I think needs to be replaced if it's not blinking.

Cheers,

Louis

Shamoye Lewis

the MOST bus requires an in signal (light) before it can give one and power on the internal board, so most units cant be tested stand alone they need a wakeup light.... which I believe comes from the Gateway controller 19 then system is powered on using a LM2596 transistor or internal loopback when the optical diag wire is triggered, so when the ring break wire is triggered the unit because a dummy loop, the electrical faults you're see could be its failing to go in ring break mode, I'm interested to know whats the fault codes if any on MMI Head Controller 7, I some how believe the LM2596/similar transistor inside the MMI head is damaged without that the optical bus wont stabilize might not even power on.... I know I said I never seen a MMI Controller kill the head and thats for sure but the MMI controller also get power through the MMI head and you can read that up at the controller connection, which means the 12V power supply's online but not the 5v, funny thing is the MMI head works without the controller, you just cant control nothing except minor from the steering wheel and that's can bus signal...

for piece of mind remove any non oem from the system, after you do that pull the fuse #12.... that will drop the power on the MMI head, if you have a power probe use it and inject 12v into the pin 1 on the head, replace the fuse an use the probe to inject grnd into Pin 2 on the head, see if it reads ZERO Flat or it makes a oscillating sound and more than Zero, if it does head is faulty it mean there's a voltage leak inside the head, defective LM2596/similar ic, over drive capacitors etc.... if you don't have a probe don't bother, its the only tool I know that can do certain test.... power probes are not very cheap so don't buy one just for this test, its a good tool though, I have models PP3LS01 and PP401AMZ01.. real time saver when doing and testing electricals, can also detect 5v lines, inline temp fuse, shorts, injectors, ecu drivers and more always makes my jobs quick and easy....

Pawel S

Thanks a lot Guys for all your replies! Luckily I do have a power probe 3, bought it because I though I would need it one day, well, this is the day.
I will do all suggested tests today and report back hopefully by end of the day.

Just to summarize everyone's suggestions, I will do the following:

1) Unplug 3rd party device between the head and screen on the LVDS cable - observe what happens
- run VCDS scan
- run optical bus diagnostics
2) check fiberoptic cables for light blinking (after cycling ignition off/on to avoid timeout) at:
- MMI control head
- CD changer
- Navigation system in the trunk
- Amplifier in the trunk

Am I missing anything else on fiberoptic loop?

3) check for fault codes if any on MMI Head Controller 7 ( is this what vccs scan will show?)

4) Control head check:

- Remove any non oem from the system
- Pull the fuse #12
- Inject 12v into the pin 1 on the head (I understand with the connector plugged in? I don't fully understand what am I looking for after injecting 12V - system to wake up? Please confirm)
- Replace the fuse 12 and use the power probe to inject grnd into Pin 2 on the head (connector must be hooked up I guess, please confirm)
- See if it reads ZERO Flat or it makes a oscillating sound and more than Zero

ltooz_a6_a8_q7

fully yet. It will show the error on anything that break in the loop and it looks like the Head Unit is bad. There must be so many good parts replaced due to bad diagnostics.
https://www.audiworld.com/forums/a8-.../#post24811415

I unplugged the after market AMI MOST optical bus without test loop, the screen is black and nothing is working. So, the blinking LED on each component may be one of the ways to check for the health of that component. I would start with the HEAD Unit.
1. Head unit.
2. CD changer.
3. DVD navigation.
4. Telephone Controller (under the seat?)
5. Satellite Unit (in the back).

You should have a test loop to disable the bad device or the one that's in question.

Cheers,

Louis

Shamoye Lewis

Louis, I don't think he is seeing any video at all on the screen, or at least I don't recall he saying he did, correct me if I'm wrong Pawel.... this could happen if the aftermarket device is bad, puzzling is he is not seeing any lights on the MMI controller, that's controlled by the MMI head... normally if any of the devices is defective the screen will still briefly show the Audi MMI Boot Logo then blank out.... and repeat it self few times, atleast the US Variants sure the rest is the same...

so I believe something is jamming the MMI head or its toasty, I know some aftermarket device that goes on the MMI head connects to the power/data harness... he mentioned he had a rear camera device, if thats stuck the MMI screen will not show because these devices use a solid state relay to switch the screen, but I don't think they will stop the MMI Controller Pad from lighting up, unless that device use a control disconnect function, if it does and its stuck then it could be the cause of all this drama...

Pawel S

Gentlemen,

This correct, I am not seeing any video on the display at all since the coffee was spilled on the pad and the MMI pad is not lit either (even the brand new one I purchased from ECS tuning). So the symptom is that the screen is black and not lit as well as MMI pad black not lit. I attached picture of the 3rd party device. And correct, there is 3rd party rear camera installed which I believe is what this additional MMI device is for.