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MELSEC-Q

 

11   TROUBLESHOOTING 

 

11.5.2 Output Circuit Troubleshooting 

This section explains trouble examples and troubleshooting methods in the output 

circuit. 

 

Output Circuit Troubleshooting 

 

 Condition 

Cause 

Corrective 

Action 

Ex

ample 1 

Excessive 
voltage is 
applied to 
load when 
output turns 
off. 

• When load is half-wave rectified inside 
  (This is typical of some solenoids.) 

QY22

[1]

[2]

D1

C

Output module

Load

 

• When the polarity of the power supply is [1], 

the capacitor C is charged. When the polarity 
is [2], the voltage charged in C plus the power 
supply voltage is applied to across D1. The 
maximum value of the voltage is approx. 2.2E. 
(This usage does not pose problems to the 
output components but may deteriorate the 
diode built in the load, causing burnout, etc.) 

• Connect a resistor of several ten K  to several 

hundred K  across the load. 

 

Load

Resistor

 

Ex

ample 2 

Load does 
not turn off. 
(Triac 
output) 

• Leakage current due to the built-in surge 

suppressor 

QY22

Output module

Load

Leakage current

 

 

• Connect a resistor across the load. 

(If the wiring from the output module to the 
load is long, be careful since there may be a 
leakage current due to the line capacity.) 

 

Load

Resistor