Baldor MN850 用户手册

5-2 Troubleshooting

MN850

Unit fails to start

1. Verify that 115VAC is present at X1 and X2 terminals.
2. Verify that 9VAC is present  at terminal J2 (see Section 2 cover removal).

1. Control board or other component may be defective.  Contact Baldor.

Unit trips during
start

1. Check parameter 73 (last trip) error code and isolate source of problem (see Table 5-1).
2. Verify that all three phases of AC input power and motor power are present (no missing phases).
3. If input contactor is used, verify AC input power is present at L1, L2 and L3 before the contactor delay time 

is complete.  If the SCR’s fire before AC power is present, the “Phase Loss” message is displayed and 
unit will trip.

4. Verify all connections at the SCR gate connections.  (Resistance check: with all power removed, the 

resistance between adjacent Red & Yellow wires at the control card connections can be checked.  
Between pins 1–2, 3–4, 5–8 etc. the resistance should be between 10 – 50 ohms

±

20%.

5. Verify there are no power factor correction capacitors on the output.  Power factor correction capacitors may 

only be connected on the line side of the control and must be switched out during starting.

6. Verify SCR are not shorted (error display “Motor SCR Loss”).  (Resistance check: with all power removed, 

the resistance can be checked between adjacent Red to Red wires at the control connections.  Between 
pins 1–4 (L3 & T3), 5–8 (L2 & T2) and 9–12 (L1 & T1) the resistance must be greater than 500k ohms.

7. If the “Shearpin” or “Overload” messages are displayed, verify that the soft–start control is correctly sized.
8. If the “Too Hot” message is displayed, verify the thermal switch connection (or jumper is installed) at J4.
9. If the “Sensing Signal” or “SCR Signal” messages are displayed, problem can be excess noise or failure on 

another circuit board.  Contact Baldor.

10.  Verify that the motor is less than 328ft.(100m) from the soft–start control.

Bad start then unit
trips

1. Check parameter 73 (last trip) error code and isolate source of problem (see Table 5-1).
2. Verify that AC input power and motor power wires are not reversed. (The motor will give an initial kick then 

start very roughly.)

3. Verify all connections at the SCR gate connections.  (Resistance check: with all power removed, the 

resistance between adjacent Red & Yellow wires at the control card connections can be checked.  
Between pins 1–2, 3–4, 5–8 etc. the resistance should be between 10 – 50 ohms

±

20%.

4. Verify there are no power factor correction capacitors on the output.  Power factor correction capacitors may 

only be connected on the line side of the control and must be switched out during starting.

5. Verify SCR are not shorted (error display “Motor SCR Loss”).  (Resistance check: with all power removed, 

the resistance can be checked between adjacent Red to Red wires at the control connections.  Between 
pins 1–4 (L1 & T1), 5–8 (L2 & T2) and 9–12 (L3 & T3) the resistance must be greater than 500k ohms.

6. Verify that the motor is less than 328ft.(100m) from the soft–start control.

SCR’s short on
first start–up

1. Verify there are no power factor correction capacitors on the output.  Power factor correction capacitors may 

only be connected on the line side of the control and must be switched out during starting.

2. Verify that the soft–start control is correctly sized.  Verify the Rated Current, Overload Trip level, and trip 

delay are correct for the application.  

3. Verify that the motor is less than 328ft.(100m) from the soft–start control.  Also, verify the motor and motor 

leads are good.

Unit trips during
ramp–up

1. Check parameter 73 (last trip) error code and isolate source of problem (see Table 5-1).
2. Verify that all three phases of AC input power and motor power are present (no missing phases).  

Check for blown fuse if “Phase Loss” message is displayed.

3. Verify that the soft–start control is correctly sized.  Verify the Rated Current, Overload Trip level, and trip 

delay are correct for the application. 

4. If the “Too Hot” message is displayed, verify the thermal switch connection (or jumper is installed) at J4.