Cebora PLASMA SOUND PC 70/T Manual De Servicio página 41

CEBORA S.p.A.
The output and power sources of Hall effect current sensor SH1 mounted on
secondary winding board (32) are connected in control board (48).
Hall effect current sensor SH1 reads the power source output current.
Thermostat (29) connected to IGBT heatsink (42) is connected to FASTON
connectors FS1 and FS2.
Given the specific configuration of the inverter (control board (48) with built-in drive
circuits, directly connected to IGBTs (30)), the drive circuits often become damaged
following IGBT failure (30). For this reason, simultaneous replacement of control board
(48) with both IGBT modules (30) it is recommended. Otherwise the new IG BT
modules controlled by the defective drive circuit would again be damaged. Similarly,
when replacing control board (48) following a fault in the IGBT module drive circuits, it
is advisable to replace both IGBT modules (30) at the same time.
IGBT board (31) 5602085
IGBT board (31) contains amperometric transformer SH1 for reading the current
circulating in power transformer primary winding (52).
IGBT board (31) contains relays RL1 and RL2 used to switch the primary windings.
IGBT board (31) contains polyester capacitors C1, C2 and C3 used to ensure
correct operation of the full-bridge inverter.
Power resistor (45) is connected to pins 1 and 2 of connector CN2 of IGBT board
(31). Power resistor (45) and capacitors C4 and C5 present on IGBT board (31) are
used to damp any fluctuations in the direct voltage supplying the inverter.
Secondary winding board (32) 5602210
Two ISOTOP modules containing the four rectifier diodes and Hall effect output
current sensor SH1 are connected in secondary winding board (32).
Secondary winding board (32) contains nozzle relays RL1 and RL3 and the reed
switch of relay RL2, which manages the arc transfer.
Two power resistors (47) which act as snubbers for the output rectifier circuit are
connected to connector CN2 pin 1 and pin 2 in secondary winding board (32).
This snubber function is performed together with other components on secondary
winding board (32).
Under rest conditions, the contacts of relays RL1 and RL2 are closed. This adjusts
the nozzle potential to the same potential as the earth lead. Under rest conditions, the
electrode in the torch is in electrical contact with the nozzle.
When the start pushbutton is pressed, the inverter activates and an appropriate
current of approximately 18 A flows in the electrode-nozzle electrical contact. At the
same moment, solenoid (16) is activated causing air to flow in the torch air circuit and
lift the electrode off the nozzle. When the electrical connection between electrode and
nozzle is broken, a discharge is generated. This ionises the air and generates a plasma
arc between electrode and nozzle. The airflow drives the plasma arc towards the
workpiece, causing a current to flow in the coil of reed switch relay RL2. When the
current is sufficiently strong to trip reed switch relay RL2, relays RL1 and RL3 activate,
opening their contacts and cutting off the arc between electrode and nozzle. Under
these conditions, the entire plasma arc is transferred to the workpiece and runs
between electrode and workpiece.
The transferred arc signal is present on connector CN1 pin 6 of secondary winding
board (32). This signal is sent to connector J8 pin 2 of display board (57).
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10/07/2019