Tweco 130i Transarc Service Manual - Manual (Page 58)

TROUBLESHOOTING 6-16 Manual 0-5282
TRANSARC 130i
6.13 Main Circuit Description
!
WARNING
Turn off power and disconnect mains supply plug from receptacle before working on the unit. Allow
two minutes for capacitors to discharge after disconnection from mains supply voltage.
A-11854
The mains supply voltage is connected via a double pole switch to the input rectifiers on the main inverter board
through an EMC filter. Overvoltage protection is provided by varistor CY1.
The rectifier output charges the main capacitor bank (C5, C6, C7, C8, C9 and C10) to high voltage. Inrush current
limiting is provided by a PTC which is then bypassed by relay J1 after a few seconds.
The primary igbt transistors (T3, T4, T5, and T6) switch the transformer primary at high frequency and varying
duty cycle. The transformer return wire is taken from the terminal ZBQY1 (the voltage at this point is approximately
half the DC bus voltage).
Secondary output voltage from the transformer is rectified by the output diodes (D1, and D2) to DC. This DC is
controlled by the PWM of the primary side igbt transistors, and is filtered by an inductor before connecting to
the welding output terminals. IGBT1 to IGBT8 control whether AC or DC output is sent to the welding terminals.
A thermal overload device (thermal switch) is fixed to the rectifier heatsink. When an over temperature occurs,
the control circuit inhibits the trigger, gas solenoid, and the welding output. The thermal overload indicator LED
on the front panel is illuminated.
The current transformer CT1 provides a signal to the control circuit to indicate both transformer primary current,
and also detect transformer saturation. The Hall effect current sensor CT2 is powered from regulated + & - supplies
and provides a voltage signal proportional to the output welding current to allow the control circuit to regulate
welding current.