Classic Mac OS debugging output
You can make the Classic Mac OS dump a bunch of debugging output to Open Firmware during boot and sometimes the screen after boot.
To do this, open Open Firmware during boot with Command-Option-O-F and enter
dev / 3013FFF encode-int " AAPL,debug" property. Then, boot with
If you want a log of this output, you should hook your machine up to the local network, then run this, replacing the IP address with whatever is available for the machine to use:
dev /packages ls " enet:telnet,10.42.0.10" io
Then connect to your machine via Telnet before booting.