Brake Igbt Test; Intermediate Section Tests; Heatsink Temperature Sensor Test - Danfoss VLT Series Service Manual

5.1.6 Brake IGBT Test

This test can only be carried out on units equipped with a
dynamic brake option. If a brake resistor is connected to
terminals 81 and 82, disconnect it before proceding. Use an
ohm meter set on diode check or Rx100 scale.
5.1.6.1 Brake IGBT Test Part I
1. Connect positive (+) meter lead to brake resistor
terminal R+ (82).
2. Connect negative (-) meter lead to brake resistor
terminal R- (81).
The reading should indicate infinity. The meter may start out at
a value and climb toward infinity as capacitance is charged
within the drive.
5.1.6.2 Brake IGBT Test Part II
1. Connect positive (+) meter lead to brake resistor
terminal R- (81).
2. Connect negative (-) meter lead to brake resistor
terminal R+ (82).
The reading should indicate a diode drop.
5.1.6.3 Brake IGBT Test Part III
1. Connect positive (+) meter lead to brake resistor
terminal R- (81).
2. Connect negative (-) meter lead to negative (-)
DC bus connector MK105 (B) on the power
card.
The reading should indicate infinity. The meter may start out at
a value and climb toward infinity as capacitance is charged
within the drive.
Incorrect Reading
An incorrect reading on any of the above tests indicates that
the brake IGBT is defective. Replace the brake IGBT in
accordance with the disassembly procedures in Section 6 or 7.
The failure of any IGBT may also lead to a failure of the gate
drive circuit supplying that device. Following the replacement
of an IGBT, always ensure the gate drive signals are tested in
accordance with the procedures in the dynamic test section.

5.1.7 Intermediate Section Tests

The intermediate section of the drive is made up of the DC
bus capacitors, the DC coils, and the balance circuit for the
capacitors.
1. Test for short circuits with ohmmeter set on
Rx100 scale or, for a digital meter, select diode.
5-10
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2. Measure across positive (+) DC terminal (A) and
negative (–) DC terminal (B) on connector
MK105 on power card. Observe meter polarity.
3. Meter will start out with low ohms and then
move towards infinity as meter charges
capacitors.
4. Reverse meter leads on connector MK105 on
power card.
5. Meter will peg at zero while capacitors are
discharged by meter. Meter then begins moving
slowly toward two diode drops as meter charges
capacitors in reverse direction. Although test
does not ensure capacitors are fully functional, it
ensures no short circuits exist in intermediate
circuit.
Incorrect Reading
A short circuit could be caused by a short in the soft charge,
rectifier, or inverter section. Be sure that the test for these
circuits have already been performed successfully. A failure in
one of these sections could be read in the intermediate section
since they are all across the DC bus.
If a short circuit is present, and the unit is equipped with a
brake, perform the brake IGBT test next.
The only other likely cause would be a defective capacitor
within the capacitor bank.
There is not an effective test of the capacitor bank when it is
fully assembled. Although unlikely that a failure within the
capacitor bank would not be indicated by a physically damaged
capacitor, if suspect, the entire capacitor bank must be
replaced. Replace the capacitor bank in accordance with the
disassembly procedures in Section 6 or 7.

5.1.8 Heatsink Temperature Sensor Test

The temperature sensor is an NTC (negative temperature
coefficient) device. As a result, high resistance means low
temperature. As temperature decreases, resistance increases.
The power card reads the resistance of the NTC sensor to
regulate fan speed and to monitor for over temperature
conditions.
1. Use ohmmeter set to read ohms.
2. Unplug connector MK100 on interface card and
measure across cable leads.
The full range of the sensor is 787 ohms to 10K ohms where
10K ohms equals 25°C and 787 ohms equals 95°C. The higher
the temperature, the lower the resistance.