SERVICE MANUAL
Transmig 165
ST
Transmig 165
ST
SERVICE MANUAL
Transmig 165
ST
Transmig 165
ST
Manual 0-5442
10-19 TROUBLESHOOTING
The mains supply voltage is connected via a double pole switch to the input rectifier Q1 through an EMC filter. Over-
voltage protection is provided by varistor CY1.
The rectifier output charges the main capacitor bank (C16, C17, C18, C19, C22 and C23) to high voltage. Inrush cur-
rent limiting is provided by a PTC which is then bypassed by relay J1 after a few seconds.
The primary igbt transistors (T1, T2, T4, and T5) switch the transformer primary at high frequency and varying duty
cycle. The transformer return wire is taken from the junction of the capacitors C20 and C21 (the voltage at this point
is approximately half the DC bus voltage).
Secondary output voltage from the transformer is rectified by the output diodes (T13, T14, T15, T16, T17, T18, T19,
and T20) 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.
A thermal overload device (thermistor) is fixed to the rectifier heatsink. When an over temperature occurs, the control
circuit inhibits the trigger, gas solenoid, wire drive system and the welding output. The thermal overload indicator
LED on the front panel is illuminated.
The current transformer TR8 provides a signal to the control circuit to indicate both transformer primary current, and
also detect transformer saturation. The Hall effect current sensor is powered from reg & - 15VDC supplies
and provides a voltage signal proportional to the output DC welding current to allow the control circuit to regulate
welding current.
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