Troubleshooting
Have a 6300 that won't boot? There is a troubleshooting section in the Service Manual, so start there.
There have been a few threads over on the VCFED forums that cover trying to troubleshoot and repair the 6300:
http://www.vcfed.org/forum/showthread.php?54771-AT-amp-T-6300-won-t-post
http://www.vcfed.org/forum/showthread.php?54605-How-to-read-parallel-port-POST-diagnostic-codes
http://www.vcfed.org/forum/showthread.php?54319-My-AT-amp-T-6300-Bricked
Additionally, there is a lot of technical documentation here about the M24, the system the 6300 was based on: http://www.olivettim24.hadesnet.org/doc.html