o.k., asked on the German E34 forum and got the following detailed information (translation here):
In a normal situation of a pixel test it looks like in the above pic.
However, if it is frozen in that position:
pull the OBC out and wait 10 minutes.
Then install it again.
It is of importance that during that time the ignition is off!
In case the problem still exists after that trial, then most probably a capacitor inside the OBC is defective.
(capacitor can be charged, but by some reason cannot discharge)
Defective capacitors can be recognized in most cases by visual inspection, either some sticky matter can be found outside the capacitor, or it shows expansions at the upper side.
See the pictures below, expanded capacitor, and in pic 2 one can see the liquid on/below the capacitors.
In such a case the capacitor has to be replaced, best by someone who has some experience with the soldering iron and soldering of electronics.
I hope I could help.
greetings fuchzger
http://home.pages.at/knalle/bilder/mk/elko1.jpg
http://www.fabiankeil.de/blog-surrog...en-500x333.jpg
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Please let us know if that helps.