Green digital dash not lighting up

[BackintheFold]

After replacing some blown bulbs, my digi-dash isn't lighting up normally.

Symptoms:
When i turn on the ignition, it flickers VERY briefly some times, and always when switching off. It looks bright when it does appear.
The odometer and trip are no longer lit up, and are unaffected by the dimmer. The dimmer still dims the heater control lights etc. (this could mean one bad earth on the dash)
My dash works when I press in the reset switch with the ignition off, so that's good news. It is just tracking down why it doesn't work from the ignition.
My boost gauge is clearly less than 1 bar (normal atmospheric pressure).Could suggest bad earth or bad power supply.

Progress:
I've been reading the wiring diagrams and the Audi test procedure for the green digi dash, as well as the internet for people with similar issues.

From the wiring diagrams the problem could be a bad earth, or a bad dimmer switch, or a poor connection on the 35 pin connector, or a duff diode in the power rail on the PCB (15), or a broken ribbon cable from the PCB to the transformer.

Questions please:
With the ignition ON, but engine off, is the odometer and trip mileage section lit up?
Are these two lights dimmed by the dimmer in this status?
Are these two lights on permanently, or only when the sidelights are switched on?
Does the dimmer alter the brightness of the green display?
What is left "on" when you push in the dimmer "minimum display" button?
Where is the bar boost gauge reading with engine off?
With the ignition on, and the dimmer set to a minimum, can the display be seen at all?
If the ignition is on, and the display is set to "minimal", and then the ignition is switched off, when the ignition is switched back on again is the display minimal still, or does it revert to "full"?
With the dimmer set low, when the ignition is switched off does the dash flicker brightly briefly?

With the ignition OFF, when you press the reset button, does the dimmer position make any difference to how bright the dash lights up?

THANKS!!

[BackintheFold]

Ok, it is a bad dimmer. Anyone have one? Specifically the part of it which is the plate with 21 ohm written on it.
Part is 857 919 093 B
Thanks


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[BackintheFold]

In more detail, I discussed the problem with Pete Knights. What he doesn’t know about these dashes isn’t worth knowing!
The big clue for mine was the odo and trip lights not lighting up-and as I had replaced one, this also reinforces that if something goes wrong, what was the last thing you did or replaced before it went wrong.

The mileage lights run through the dimmer, and if the dimmer is missing/unplugged/broken then the lights won’t light up and the dash resets to minimum display level-so minimum you can’t see it lit up.
The dimmer being the issue is not covered by the Audi workshop repair notes, or Phil Payne’s site, or anywhere that I had seen. I looked at the wiring diagrams to find the link-but even so the wiring diagrams do not show that the dimmer affects the green parts lighting up-but it does. (It’s possible that the diagrams I have are not the right one for my dash!!)

The Digi dash itself is complex, and before messing around withnitnirnopenjnb it up, the first check is that everything else works-the fuses, the earths, the dimmer and 2 dash backlights.

There are also three versions of the green dashboard, so even if you navigate the wiring diagram, be sure you have the right one!

Pete was extremely knowledgeable, and emphasised that taking the unit apart is a bad idea if you don’t have expert knowledge. He can repair the dash, but fiddling with it can make that impossible, so just work on the easy stuff outside of the dash itself.

[urquattr085]

Great information and sound advice.
Sounds like you're on the road to getting sorted.

I got the impression Pete knows quite a lot about these cars in general & others have also said he is THE guy for digi dash work.

[mikes2]

Pete was spot on when I contacted him about the orange dash fault on my MB.

He didn't charge much at all - around £60 to fix a flickering display.