missing arrows in boot 16-17&20

What is the name of the manufacturer and model of the equipment you are working on? 

First check is the CB1 under the system. its a circuit breaker that cuts power from the batteries to the system.

Boot Test System does not complete pre-charging, PRECHARGE VOLTAGE ERROR is displayed, CB1 under the C-Arm is not closed. Verify that CB1 is turned
on. If not, turn it on. If it trips, call service technician.F4 in Cap/Power Module is open. The PRE-CHARGE VOLTAGE ERROR message may occur if the
battery charger is set to higher than the normal 225 VDC output in normal charging mode, with battery pack fully charged. This is especially applicable if AC power is at the low voltage limit (10 percent lower than normal), with 50 Hz AC power.

16 Precharge complete. If boot-up fails on this arrow, check Precharge circuitry, Generator
Events Log, and Battery circuit breaker.
17 Filament ramps. If bootup fails on this arrow, check Filament drive circuitry on Filament
Driver PCB and Generator Driver PCB.
18 System checks C-Arm battery. If boot-up fails on this arrow, check Generator Events Log,
C-Arm batteries, and INV_B_SEN signal on Filament Driver PCB and Generator Driver PCB.

20 Boot-up complete (does not display).

how do you check the precharge circuitry?