As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WILL NOT START. HANGS BETWEEN 0-10% RPM. SHUTSDOWN WITH APU FAULT LIGHT ON. REFER TO MM-49-61-00, CODE B1. NO POWER BEYOND MAIN CONTACTOR, NO POWER TO CONTROL SIDE OF CONTACTOR. REPLACED RELAYS K117 & K197, AND APU CONTROLLER. APU START OKAY.