Dear Olaf,

I have faced the same problem many times with ST 48Z02. In my case, the RAM doesnot work. It has to be just replaced. Looks like some particular location in the RAM got damaged if the reset was not proper or the RAM was enabled before a proper reset and some location was written on to.

May be by using a supervisory chip like MAX 691 solves the problem.

Regards,

Mohit