CHAPTER 5: MAINTENANCE
DUAL PULSE 125
STORED ENERGY RESISTANCE WELDING POWER SUPPLY
5-4 990-270
Troubleshooting
If the circuit breaker trips repeatedly, one of the following is probably the cause:
a) Overload - Exceeding the duty cycle.
b) Lockup of the output SCR, Q6 (switches ON, but not OFF).
c) Shorting of the charging Triac Q1.
d) Charge shunting SCR, Q2, shorted or locked ON.
e) Charging bridge rectifier diode(s) shorted.
f) Malfunction in the charging regulator which turns on the Overvoltage Protection Lockout
Circuit.
g) Malfunction or improper adjustment of the Overvoltage Protection Lockout Circuit.
h) Defective circuit breaker.
i) Miscellaneous short circuits or misconnection of the pulse transformer or the control
board.
1. Test the Triac by removing U1 on the Control Board. This should switch the Triac OFF and no
current should flow. If it does not turn off, replace the Triac.
2. Test all diodes for shorts by using an ohmmeter.
3. Disconnect the capacitor bank. Charge the bank with an external 400 volt DC power supply.
After five minutes, the steady state current should be less than 12 milliamps. If it is not, one or
more of the capacitors is shorted. Discharge the bank with a 500 - 2000 ohm, 25 watt resistor
and replace the defective capacitor.
CAUTION
Do not discharge the bank by directly shorting it with a screw-driver, clip lead, or the
like. The stored energy could be sufficient to melt them in an explosive manner.
4. Replace Cover - After performing any modifications and checking internal connections replace
cover and tighten screws.
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