Found out a few more things on the cluster screen that goes bad and would like to share it.
I took apart a 2000 Audi A4 cluster as my second cluster to experiment with. The middle screen was missing about 20 lines total.
I have played with the screen and discovered that the issue is in the connection between the two flex cables, the one that holds the chip and the one that goes to the lcd.
By applyng pressure on the connection, with a cotton swab, i was able to bring all the lines back , with up and down sweeping motions. The problem is that the lines would gradually start disappearing. Don't use anything sharp doing that because you'll damage it ireversibly.
I tried heating the area a little bit with some hot air from the smd rework station and then redid the motion but it didn't help...seemed to make it even worse.
So, by me playing with the screen, i actually made it worse at the end.
Also, i have discovered that dimmer pixels are not due to the baclight going bad, they are also due to the bad connection.
I'm not sure yet what causes single pixels to go bad since i haven't seen one of those yet but those i attribute to something else than the flex connection. What could also be the cause is that LCDs need ac voltage with frequency between 40Hz and 60Hz to operate and DC voltage might damage the screen for good... so if DC voltage would be induced in any way, would actually cause burnt or dim pixels.
With all this said, it looks like we're still at square one... we found the problem but attempting to fix it only makes things worse.
On the other side i have been comparing the A4 dashboard and lcd to the S4 and they have exactly the same connections for the lcd and the same voltages and signals which makes me believe the lcd is the same. This might mean that the screen is exactly the same on the audi's that have the screen that looks like this one. The numbers on the lcd driver chip though don't match...not sure why.
I have also interfaced the S4 dashboard to a motorola HC11 evaluation board but it seems that the motorola would have to be about 10 times faster to keep up with only reading the data coming from the lcd. The data rate for the lcd seems to be close to 1 Mbytes/sec which is a lot but is needed for all those animations.
I will have to find another faster interfacing platform to be able to read the data and interpret it but i think i'm one step closer to finding a solution.
Thanks for reading!

 

Those are LEDs not LCDs in the cluster by the way... They do not need AC frequency.

 

the led's don't need AC but the LCD does.
If the lcd ever get's dc, it's damaged.
I initially thought that dimmer areas in the lcd might be due to the led's going bad or weak in the backlight but now i saw that it's the lcd not the leds.

 

Does the cold have something to do with this? I need to take it in to be replaced under warranty.

 

My S4 Cluster does not have any LCD's what are you talking about?

 

One that shows the clock and date, the middle one wfor DIS and one that shows the odometer and current trip distance. All these three are lcds with LED backlight.

 

mine was replaced under CPO i figure itsa gonna last for 50k unless the new clusters are updated???

 

LCD's have a problem with low temps and they look like they are blurry when animations are present. That is why behind the big lcd there is a heater.So if you are only seeing this blur thing, ignore it as it's fine.
If you are missing lines or pixels, more noticeable in very cold or very hot temps, get it replaced under warranty, because it's all downhill from here. It won't get better. Sooner or later it will be unusable.

 

Arrays to me.

Bruce
MSEE

 

I think mileage is not the issue and the issue is related to cycles of extremely cold or hot temperatures, which back and forth cause the flex connection failure.