Mode switch on the rear panel. There is a silk screened table on the component side of the circuit board. It reads as follows:
1 0
1 Video 75Ω ON OFF
2 Serial IN RS232 MIDI
3 Chase Mode Rechase Free
4 Rechase 1 2
5 TC out timing Analog Digital
6 Midi TC Int TC Ext TC
7 V Sync PB Off On
8 Controller Type 1 Type 2

Factory default: All at "1"

Internal S2, S3 all at "on"