Successful replacement of my OBC... (archive)

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This is just a short story regarding a recent change of
the on-board computer (OBC) in my 850. As some of you have
seen, I posted earlier some questions regarding changing
the OBC as a total of seven (!) columns of bits on my
display were blown.

With a lot of help from Lez, I got the part number and
copies of the repair manual for how to change this
particular part. Last week I ordered the new OBC from my
local BMW dealer and it all went in around 300 US dollars.

I also had some excellent descriptions from both from Mr.
Spears and Mr. Holm (sent to me by PMB) on how to both
change and clean the OBC, but I finally decided to go for
the simple solution to buy a new unit.

I had two ways of getting into the back of the OBC to be
able to push it out. Either I could remove the air vent
above the center console or I could remove the radio
located below the OBC. I had some people warning me from
trying to go the radio way as it seems that would be
fairly tricky. The radio is secured by two covered screws
which I was told would not be hex-key screws. Maybe my
car is different, but I managed to remove the screws and
the radio with a hex-key in just one minute.

After removing the radio to the side to be able to get
my hand into the location where the radio normally fits,
it is very simple to press in the large, lower clip which
holds the radio in place from the lower side. Once that
is done, the OBC comes ut, but then locks on three tabs
on the upper side which you need to depress. Turns out
that the dash is so flexible that it is simple to push
the OBC slightly downwards to have these tabs release the
OBC that then simply pops out.

At that time I simply disconnected the cable from the
back, connected it to the new OBC and pushed it back in
and screwed the radio back on. Doing it all very calmly
and slowly, it just took me 8 minutes to get it done. I
can now finally read what the damn computer tries to tell
me ;-) I just hope it won't be just to deliver serious
error messages.

Looking at the old and new computers, I was amazed about
its construction. The whole back side is open in a lot of
places with a lot of holes which allow you to see the
cables and the chips inside the computer. Looking at where
it all is located and how dusty it is in there, I really
understand Mr. Holms description on dirt. I cleaned the
interior as much as I could and for a while I even thought
of covering these small holes, but as that maybe causes the
OBC to overheat I simply didn't dare to do it. Some experts
out there who know if this unit develops a lot of heat? It
probably is not a good idea to cover those openings, but
it is evident that there is where the problem is.

Finally a big thanks to Lez who always has time to answer
questions and to the previous members who wrote so good
descriptions of how to do this, that it made my life
simpler today when I made the swap.

P.S Anyone has some further information on a manual for the OBC. There seems to be a lot of functionality in there now documented properly in the car documentation.

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