An STo (Safe Torque OFF) or SToF (Safe Torque OFF Hardware) will occur on a GA800, FP605, GA500, or HV600 drive when one or both of the safety inputs (H1 and H2) is open (OFF). The drive will coast to a stop and remain in a "not ready" state until one or both of the safety inputs (H1 and H2) return back to a closed (ON) state.

• Note: An STo or SToF is considered an alarm (minor fault).

Refer to the table below to determine when an STo or SToF will occur:

Input Status		Keypad Display	Drive Output Status	LED Status Ring	Digital Output Status	Modbus/MEMOBUS Register 0020H (Drive Status 1)
Terminal H1	Terminal H2				H2-xx = 21	Bit C	Bit D
ON (Closed)	ON (Closed)	-	Drive Ready	Ready (Illuminated)	OFF	0	0
OFF (Open)	ON (Closed)	SToF (Flashing)	Safety Status	ALM/ERR (Flashing)	OFF	1	0
ON (Closed)	OFF (Open)	SToF (Flashing)	Safety Status	ALM/ERR (Flashing)	OFF	1	0
OFF (Open)	OFF (Open)	STo (Flashing)	Safety Status	Ready (Flashing)	ON	0	1

The image below illustrates the H1, H2, and HC (common) connections on the terminal board and the factory jumpers if an external safety input is NOT present. Terminals SN is used if an external 24VDC supply is being used.

Follow the steps below for troubleshooting an STo or SToF fault on a GA800, FP605, GA500, or HV600 drive:

External Safety Input NOT Present (Factory Jumpers in Place)

1. Verify jumpers are present on H1/HC and H2/HC terminals and connections are tight and secure.
2. Ensure the Terminal board is NOT loose. 
3. Remove power to the drive.
   • Caution: It is recommended to verify 10VDC or less is present on the DC bus before performing any service work.
4. Remove jumpers and ALL control wiring (digital inputs, communication, etc.). Apply power and check for 24VDC between H1/HC and H2/HC.
   • If 24VDC is NOT present, the issue may be within the terminal board, control board, or more internal to the drive. It is recommended to have an ASP (Authorized Service Provider) perform any repairs.
   • If 24VDC is present, add non-factory jumper wires between H1/HC and H2/HC terminals.
     • If STo or SToF does not clear, the issue may be within the terminal board, control board, or more internal to the drive. It is recommended to have an ASP (Authorized Service Provider) perform any repairs.

External Safety Input Present (NOT Using External 24VDC)

1. Verify connections are tight and secure on H1, H2, and HC terminals.
2. Remove power to the drive.
   • Caution: It is recommended to verify 10VDC or less is present on the DC bus before performing any service work.
3. Remove connections on H1, H2, HC terminals and ALL control wiring (digital inputs, communication, etc.). Apply power and check for 24VDC between H1/HC and H2/HC.
   • If 24VDC is NOT present, the issue may be within the terminal board, control board, or more internal to the drive. It is recommended to have an ASP (Authorized Service Provider) perform any repairs.
   • If 24VDC is present, add non-factory jumper wires between H1/HC and H2/HC terminals.
     • If STo or SToF does clear, troubleshoot safety controller or look for a open safety input.
     • If STo or SToF does not clear, the issue may be within the terminal board, control board, or more internal to the drive. It is recommended to have an ASP (Authorized Service Provider) perform any repairs.

External Safety Input Present (Using External 24VDC)

1. Verify connections are tight and secure on H1, H2, and SN terminals.
2. Remove power to the drive.
   • Caution: It is recommended to verify 10VDC or less is present on the DC bus before performing any service work.
3. Remove ALL control wiring (digital inputs, communication, etc.). Apply power and verify 24VDC is preset across H1/SN and H2/SN terminals.
   • If external 24VDC is NOT present, troubleshoot safety controller or look for an open safety input.
   • If external 24VDC is present, remove the external 24VDC and add a jumper across H1/H2 and SP
     • If STo and SToF does clear, check the wiring for the external power supply
     • If STo and SToF does not clear, the issue may be within the terminal board, control board, or more internal to the drive. It is recommended to have an ASP (Authorized Service Provider) perform any repairs.