Green digital dashboard diagnosis - Audi ur-quattro

The most common problem with the green digital dashboard is the power supply unit being damaged by incorrect use of jumper (starter) leads. It is imperative that the recipient vehicle is protected with surge suppressing leads - either separate ones (e.g., Sealey PROSAF12) or jump leads with built-in protection. Always connect and disconnect jump leads with the ignition switched off on both cars.

Check also that Fuse 4 is rated at 15 amps or below. This fuse protects the digital dashboard power supply.

If damage has already occured, it may be limited to the voltage converter. Where the dashboard is in miles (feature code M20) it is shipped by Audi in two parts - the dashboard itself (857 919 038L) and its power supply - actually a static invertor - (857 919 041A). The dashboard costs twice as much as the power supply and the two together exceed £1,000. For this reason, it is important to determine which of the two components has actually failed.

• Remove steering wheel - note that the indicator stalk must be centred during reassembly (40NM).
• Remove screws under top lip and bottoms of binnacle sides.
• Lift off binnacle cover - care with sensor attached on left side.
• Detach cables from dashboard switches and remove switch frame. Take particular care with the main light switch - it is very easy to crack the frame.
• Remove screws holding digital dashboard unit.
• Unplug and remove digital dashboard unit.
• Remove the two screws holding the voltage converter to the back of the unit at the terminals end.
• Pull out the foil protecting the seven connections. From below, they are:

  Contact	Colour
  U or UDD	brown
  15 or NC	green
  31 or G	yellow
  UV	grey
  F	violet
  F'	blue
  UK	red

• Reconnect the dashboard unit and switch on the ignition. Be careful not to cause a short circuit between any of the pins when making the following measurements.
• Attach a voltmeter to contacts 31 and U_V - should be 5 volts
• Attach the voltmeter between contacts U_V and U_K - should be 26 to 29 volts.
• Attach the voltmeter between contacts 15 and 31 - should be 12 volts. If not, disconnect power and carefully desolder the wires - soldering iron should not exceed 100 watts. See below. Reconnect power and measure the detached wires again. If the voltage is still not correct, replace the dashboard unit. Otherwise replace the voltage converter.
• Attach the voltmeter between U_D and 31. Should be 11 volts.
• Switch the voltmeter to alternating current and measure the voltage between contacts F and F' - should be 3 to 4 volts.
• Loosen the mounting screws again and replace the protective foil.

If there is no power at all on the power supply, the fault may be a blown choke coil on the main motherboard. Instead of replacing the protective foil, proceed as follows:

• Desolder the ribbon cable attaching the power supply to the motherboard. Use either a solder pump or a solder wick (e.g., Servisol SOLDAMOP) to remove all traces of solder from the ends of the wires - they must all come out as one unit. Remove the power supply.
• Remove the screws from the back of the display unit, noting their positions.
• Split the display unit and remove the two screws that hold the motherboard in just below the 35-pin connector.
• The motherboard will now come away from the housing. The odometer block remains attached via a ribbon cable.
• Identify the choke - it is an encapsulated coil of copper wire soldered to the motherboard just next to the common Pin 8/Pin 9 land on the board.
• Check between the soldered ends for continuity.

If the power supply shows battery voltage between pins 15 and 31, but not the 26-29 volts between U_V and U_K, the voltage converter is most likely defective.

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