The TEAC A-1500's Service Manual was instrumental in reviving this classic reel-to-reel. Not only does it have the schematics, exploded parts diagram and parts list, it also provided mechanical adjustment information that approximate factory default settings.
Text excerpt from page 14 (click to view)
Q2903 with FET always is "OFF" at DC input.
NON REG 7.2V REG circuit
DC JACK input
Voltage detective circuit
Vcc DC input lived DC input "ON"
with JACK : OPEN "OFF" detection with out JACK : GND Short circuit
Battery voltage BATT.-DET detection
7-7. MAIN BATTERY CIRCUIT SECTION BLOCK DIAGRAM
VBATT=0 Charging off Vcc Lithium ion battery Current Voltage circuit section section LED_R Completion : Green light up CHG SW When the battery is installed , its turned "ON". RESET CHARGE-ON_L VCR-H Charge control IC System microcomputer LED_G