INSTRUCTIONS for
F-15-593-B
SVI-450i/DP - 450i Power Board Balancing
P/N 674991
November, 2003
Electric shock can kill! Precautionary measures should be taken to provide maximum protection against electrical
shock. Be sure that all power is off by opening the line (wall) disconnect switch or circuit breaker before attempting
any inspection or work on the inside of the power source.
Important:
• Power boards must be replaced in matched pairs and
balanced.
• Care must be taken not to damage the Kapton insulation between the isobar and heatsink.
Equipment Needed:
PB1
• Potentiometer adjustment tool.
• Two Digital Multimeters with a resolution of at least 3 1/
2 digits.
• Remote Hand Control HC-3B or HC-4B.
• Input Power Source: Highest line (up to 506 VAC, 60Hz)
• Shorting cable, 15’ #8 AWG cable with male twist lock
connector (PN - 1373-3936) on both ends.
Procedure:
1. Remove the top and side covers of the power supply.
2. Locate the Input Voltage Terminal Board next to the
Inverter Control Board (ICB) at the top of the machine. Verify that the unit is strapped for 460 VAC
input and re-strap if necessary.
3. Locate the Inverter Power Boards on which are
mounted 16 MOSFETs per board. These boards are
located toward the front of the machine on either side.
While facing the front of the machine, the Power
Board on the left will be referred to as PB I and the
Power Board on the right is called PB2. (see Fig. 1)
4. Find two potentiometers (R8 and R28) which are both
located on each Power Board. These potentiometers
are located a little less than half way down from the
top of both PB 1 and PB2. (see Fig. 2)
5. Measure the resistance of these potentiometers with
an ohmmeter and adjust each one to 5 ohms. Potentiometer R8 can be measured by placing an ohmmeter between the drain of Q3 (see Fig. 3) and the
gate resistor R10. Potentiometer R28 can be measured by placing the ohmmeter between the drain of
Q14 and the gate resistor R31. If the ohm meter
being used contains a relative option, then a more
accurate reading can be gotten by putting the multimeter in ohm mode; connecting the meter leads together, and pressing the relative button on the meter.
This preceedure zeros out the resistance effect of
the leads.
PB2
Fig. 1 - Location of Power Boards
Potentiometers
(R8 & R28)
Fig. 2 - Location of Potentiometers
6. Place one of the voltmeters across capacitor C6 on
PB1 and the other across C6 on PB2. (see Fig. 4)
7. Short circuit the power supply by using a 15' 8 AWG
cable to connect the positive output of the power
supply to the negative output.
8. Connect the Remote Hand Control to the power supply by means of the 14-pin receptacle at the rear
panel of the machine marked “Remote Control”. Turn
the Output pot on the Remote Hand Control full
counter clockwise to “Minimum” for minimum current (if an HC-4B is used, turn the Arc Force pot to
minimum also). Make sure the contactor switch is in
the “Off’ position and the CC/CV switch is in the “CC
(Stick/Tig)” mode.
9. Turn the Main Power switch on the rear of the machine to the “ON” position. Then turn the Contactor
switch on the Remote Hand Control to the “ON” position. At this time, the power supply should be putting out power. Adjust R160 the Inverter Control Board
(ICB) until the short circuit output current is between
90 and 110 amps.
10. Check the voltages across C6 on PB1 and PB2. No
calibration is required if the voltage difference between the two boards is 15 volts or less. If the voltage difference is greater than 15 V go on to the next
step.
11. Make sure the power to the machine is off and
allow the voltage across capacitors C6 on PB1
and PB2 to bleed down to less than 10V before
readjusting the potentiometers. The resistance of
potentiometers R8 and R28 for a particular board
must increase if the voltage across C6 is higher than
that of the opposite board or decrease if the voltage
across C6 is lower than that of the opposite board.
The amount of potentiometer adjustment required
will vary. Equally increase or decrease the resistance
of both (R8 and R28) by only 1 ohm if the voltage
imbalance is less than 30V. Increase or decrease
resistance of both potentiometers (R8 and R28) by 2
ohms if the voltage imbalance is greater than 30V.
R8 and R28 must be adjusted to the same resistance.
12. After making these adjustments to the potentiometers, repeat steps 10 to check the balance again.
Several adjustments might have to be made before
the voltage imbalance is less than 15V. As the imbalance approaches 15V, smaller adjustments of less
than 1 ohm should be made on the potentiometers.
Always raise the potentiometer resistance of the
board with the higher voltage and lower the potentiometer resistance of the board with the lower voltage.
Fig. 3 - Location of Potentiometers & Drains
Fig.4 - Placement of Voltmeter Leads
F-15-593-B 11/2003