Danfoss VLT series, Service Manual

Page: 90 / 158

5-24
VLT is a registered Danfoss trademark
5.2.10 IGBT Switiching Test
Using the test cable 176F8439 while the drive is powered
and the DC bus is disabled, a simple test can be made to
determine if the IGBTs are actually turning on.
Before proceeding, verify that the DC bus is in fact disabled.
1. Disconnect cable from connector MK105 on
power card. With a volt meter, measure
between white lead of cable disconnected from
MK105 and output terminals U, V, and W in
turn. Switch between AC and DC scales.
Voltage should read nearly zero.
2. Measure between black lead of same cable and
the output terminals U, V, and W in turn. Voltage
should read nearly zero.
With DC bus disabled, proceed using a DVM set on diode
scale.
1. With drive in a stop mode, connect positive (+)
meter lead to black lead of MK105 cable
disconnected from power card.
2. In turn connect negative (-) meter lead to drive
output terminals U, V, and W. Meter should
indicate a diode drop.
3. Leaving positive meter lead connected to cable
MK105, run drive at 30 Hz.
4. In turn, again connect negative (-) meter lead to
drive output terminals U, V, and W. Meter should
indicate effectively a short circuit or around a
0.035 diode drop which indicates lower IGBTs
are turned on and shorting meter to negative
bus.
NOTE
Some voltage leakage within unit may cause
meter to indicate a small negative voltage drop.
5. Repeat test for positive (+) or upper IGBTs.
6. With drive in a stop mode, connect negative (-)
meter lead to white lead of MK105 cable
disconnected from power card.
7. In turn, connect positive (+) meter lead to drive
output terminals U, V, and W. Meter should
indicate a diode drop.
8. Leaving negative meter lead connected to cable
MK105, run drive at 30 Hz.
5.2.11 Brake IGBT Test
Use the signal test board to test the operation of the dynamic
brake IGBT and gate drive circuitry. The following procedure
can be used to force the brake circuit to activate for testing.
1. Connect signal test board to connector MK104
on control card.
2. Set voltage test switch labeled Over V to ON
position.
3. Turn potentiometer on test board until brake
circuit activates. This causes brake IGBT to turn
on and off at approximately 1.2 KHz. Duty cycle
(pulse width) increases as potentiometer is
increased.
4. Measure with oscilloscope or DVM at terminal
13. Terminal 13 represents gate signal to brake
IGBT. This should be 4.04 VDC when brake is
OFF and drop to zero when brake is ON.
5. Measure with oscilloscope or DVM at terminal
14. Terminal 14 is a logic level (5V) signal
representing voltage across brake IGBT. This
should measure 5.1 VDC when brake is OFF
and drop to zero when brake is ON.
Incorrect Reading
If the signal on terminal 13 is not correct, first check that the
drive is correctly programmed for dynamic braking (parameters
400 - 404). If the programming is correct, replace the control
card in accordance with procedures in Section 6 or 7.
If the signal on terminal 13 is correct but the signal on terminal
14 is not, the brake IGBT gate signal must be checked to
determine whether the fault lies in the IGBT or the gate driver
card. See Gate Drive Signal Tests (5.2.9).
9. In turn, again connect positive (+) meter lead to
drive output terminals U, V, and W. Meter should
indicate effectively a short circuit or around a
0.035 diode drop which indicates upper IGBTs
are turned on and shorting meter to positive
bus.
NOTE
Some voltage leakage within unit may cause
meter to indicate a small negative voltage drop.
Incorrect Reading
An incorrect reading indicates some of the IGBTs are not
turning on. Replace the IGBT module in accordance with the
disassembly instructions in Section 6 or 7.