92 735i - OBC power issues.

Once in a while, in my 1992 735i, the OBC computer doesn't come on when I turn the car on.
At first I thought it was the bulbs had burned out -- so I set the max mph alert
to 30mph.
Today; it failed to come on -- and; I went to 35, 40, 70 -- and no alarm.
On one (of about a dozen times) "ignition on" the OBC powered up. Clock was a few minutes slow.
I checked the fuses (replaced them actually) still -- same symptoms. This is not "every day" just "once in a while" and when it happens, I can turn the ignition on & off 30 times w/o it coming on.
Everything else works fine; so it appears something specific to the OBC -- Could it be the OBC or some connection to it?
Thanks -josh
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IIRC there is fuse inside, it also has its own NiCd battery that could be on its way out.
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<snip>
Thanks. Is it a soldered battery or socketed? I guess I'll find out.
Thanks -josh
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