The Power Supply Module (PSM) sets the major alarm for INP1 circuit failure . Typically, this is observed while replacing the PSM or after the system boots up in Junos OS 15.1F5.

Example:

After replacing the PSM (or after bootup), the alarm for PSM with "INP1 Circuit Failure" was observed. This could be a false alarm.  

To verify whether it is a false alarm or not, use the following command:

lab@Juniper_lab> show chassis environment psm 10   

PSM 10 status:
  State                      Online
  Temperature                OK                                     
  AC Input                   Feed       Voltage(V)  Current(A) Power(W)
                             INP0         237.50      3.40      807.50
                             INP1         240.00      0.00      0.00  
  DC Output                  Voltage(V) Current(A)  Power(W)   Load(%)
                               52.00      12.50      650.00     26.00
  Hours Used                 122


lab@juniper_lab> test chassis psm read status slot 10

OVP (Over Voltage)             : 0
Short pin disengage            : 0
OTP (Over Temperature)         : 0
FAN failure                    : 0
Output ORing FET failure       : 0
INP0 AC voltage out-of-range   : 0
UVP (Under Voltage)            : 0
OCP (Over Current)             : 0
 
Clear Share Fail alarm over I2C: 0
Supply OFF over I2C            : 0
Fan speed set to max over I2C  : 0
Fan speed set to min over I2C  : 0
ORing failure detect over I2C  : 0
ATS position                   : 0
LED Test over I2C              : 0
5VDC OFF over I2C              : 0
 
5VDC voltage out-of-range      : 0
5VDC OCP (Over Current)        : 0
N/A                            : 0
PFC bus voltage out-of-range   : 0
N/A                            : 0
Eeprom Write Enable            : 0
INP1 present                   : 1
INP0 present                   : 1
 
Supply Shutdown                : 0
N/A                            : 0
N/A                            : 0
Active INP at the time         : 0
INP1 AC voltage out-of-range   : 0
Active current share fail      : 0
5VDC Shutdown                  : 0
LED Test in progress           : 0
 
Supply Firmware Ready          : 1
Supply switched OFF            : 0
INP1 AC voltage Too-High       : 0
INP1 AC voltage Too-Low        : 0
INP1 AC voltage Too-Too-Low    : 0
INP0 AC voltage Too-High       : 0
INP0 AC voltage Too-Low        : 0
INP0 AC voltage Too-Too-Low    : 0
 
Eeprom Write Enable mask       : 1
N/A                            : 0
INP1 Circuit failure           : 0  <--- 
INP0 Circuit failure           : 0  <---
Pri & Sec MCU comm lost        : 0
52VDC current SHARE is OFF     : 0
5VDC output is OFF             : 0
52VDC output is OFF            : 0
 
Clear Share Fail alarm mask    : 1
Supply OFF mask                : 1
Fan speed set to max mask      : 1
Fan speed set to min mask      : 1
ORing failure detect mask      : 1
Input Feed Selected            : 1
LED Test mask                  : 1
5VDC OFF mask                  : 1

You can also look into the chassisd logs; the newly inserted PSM fails at pem_tiny_ac_input_self_test.

Apr  14 18:39:11  send: red alarm clear, device PSM 10, reason PSM 10 Not OK
Apr  14 18:39:11  pem_tiny_ac_input_self_test: PSM 10
Apr  14 18:39:11  pem_tiny_ac_input_self_test: Default INP: INP0
Apr  14 18:39:11  pem_tiny_ac_input_self_test: Switching to INP1
Apr  14 18:39:11  pem_tiny_ac_input_self_test: Switching to Non-Default - attempt 1
Apr  14 18:39:11  pem_tiny_ac_input_self_test: New INP: INP0 Old INP: INP0
Apr  14 18:39:11  pem_tiny_ac_input_self_test: Input circuit switch NOT successful. New inp INP0
Apr  14 18:39:11  pem_tiny_ac_input_self_test: Switching back to INP0
Apr  14 18:39:11  send: red alarm set, device PSM 10, reason PSM 10 INP1 Circuit Failure 

This issue has been reported in  PR1203005 - [MX2020/MX2010] "PSM INP1 Circuit Failure" alarm seen after reseating AC PSM​

Work-around to clear the alarm: 

Option 1

• Try reseating the PSM.

Option 2

1. Remove PSM from the chassis.
2. Change the DIP switch setting to have only INP0 expected. The DIP switch settings are documented here .
3. Plug in PSM to the chassis.
4. Wait for the 'Wrong Input Feed Selection for PSM 10' alarm to show up in the system.
5. Now change the DIP switch to have both feed expected.