I recommend switching on logging first to be able to debug changes and operations we made. OpenLDAP logs to the facility "local_4". Check your syslog config to see where these log messages are written or if they are recorded. On a SuSE 9.3 machine with syslog-ng the messages are written to

You now can set the log level in the slapd.conf. Change the parameter
to a appropriate number. You'll find the bits to set in the manpage of slapd.conf (search for loglevel). For example if you want to trace connection management (8) and search filter processing (32), then set loglevel to 40.