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CHAPTER 7: MAINTENANCE
875DP/500DP/500HV DUAL PULSE
RESISTANCE WELDING
POWER SUPPLIES
7-10
990-290
To adjust the trimpots, press [ENTER] to display the calibration screen listing the trimpot
adjustments. Adjust the trimpots as instructed on the screen.
NOTE:
The current measured at TP5 must not drift more than ±1.5
• •
A.
Replace the cover and top screws. Securely tighten all screws.
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. See Control Board
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 mis-connection of the pulse transformer or the control board.
x
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.
x
Test all diodes for shorts by using an ohmmeter.
x
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.
WARNING:
Do not discharge the capacitor bank by shorting it directly to ground. The stored energy
could be sufficient to melt the shorting tool in an explosive manner.
After making any repairs and checking the results, replace the cover and tighten all screws.