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TESTING GATE DRIVE
FIRING CIRCUITS
CAUTION: The gate firing signals are referenced to the negative DC Bus and are therefore at Bus
potential. Extreme care must be taken to prevent personal injury or damage to equipment. Oscillo-
scopes, when used, should be equipped with isolation devices.
The individual gate drive firing pulses originate on the interface board.
These pulses leave from connector MK1 and are distributed to each
phase via the Gate Drive Board. An oscilloscope is the instrument of
choice when observing waveforms; however, when a scope is not
available, a simple test can be made with a DC voltmeter. When using
a voltmeter, compare all the gate pulses to one another. A missing
gate pulse will show no reading and an incorrect gate pulse will generally
read more or less than the others. At very low frequencies (below
10Hz) the voltmeter will tend to bounce around as the pulse rises and
falls. Above 10Hz the voltmeter will remain stable. When testing with
an oscilloscope, the test points are the same. This test can be made at
the interface board or at each gate card output to its respective IGBT.
These tests can be made with or without a motor. However, it is
generally safer to have the motor disconnected.
TESTING AT THE INTERFACE BOARD
Use an oscilloscope or an analog or digital DC
voltmeter set for 10VDC. Connect the negative (-)
meter lead or scope ground to pin 1 of connector MK1
of the interface board. With the positive (+) meter lead
or scope probe compare the readings of pins 13, 14,
17, 18, 21 and 22 of connector MK1. Remember,
with the voltmeter the running speed of the VLT must
be above 10Hz. A voltmeter will read an average
voltage of 2.3VDC and the scope will exhibit a
waveform similar to that shown to the left. If any of the
readings appear incorrect, replace the interface board.
Test again since the gate card may be loading the
source and pulling down the signal. If replacement of
the interface board does not correct the problem,
replace the respective gate card.
Pins 21 and 22 feed the "U" phase.
Pins 17 and 18 feed the "V" phase.
Pins 13 and 14 feed the "W" phase.
GATE DRIVE SIGNAL AT
INTERFACE BOARD MK1
5V/DIV DRIVE IN RUN AT 10HZ
100uSEC/DIV
