Danfoss VLT Series Service Manual page 13

GENERAL
TROUBLESHOOTING TIPS
Prior to diving into a repair, here a few tips that if followed will make the job easier
and may prevent unnecessary damage to good components.
1. First and foremost respect the voltages produced by the drive. Always verify
the presence of line voltage and bus voltage before working on the unit.
Also remember that some points in the drive are referenced to the negative
bus and are at bus potential even though you may not expect it.
2. Never power up a unit which has had power removed and is suspected of
being faulty. If a short circuit exists within the unit, applying power is likely
to result in further damage. The safe approach is to conduct the Static Test
Procedures. The static tests check all high voltage components for short
circuits. The tests are relatively simple to make and can save money and
downtime in the long run.
3. The safest method of conducting tests on the drive is with the motor
disconnected. In this way a faulty component that was overlooked or the
unfortunate slip of a test probe will generally result in a unit trip instead of
further damage.
4. Following the replacement of parts, test run the unit with the motor
disconnected. Start the unit at zero speed and slowly ramp the speed up
until the speed is at least above 40 Hz. Monitor the phase to phase output
voltage on all three motor terminals to check for balance (an analog voltmeter
will work best here). If balanced the unit is ready to be tested on a motor. If
not, further investigation is necessary.
5. Never attempt to defeat fault protection devices within the drive. This will
only result in unwanted component damage and may result in personal
injury as well.
6. Always use factory approved replacement parts. The unit has been
designed to operate within certain specifications. Incorrect parts may effect
performance and result in further damage to the unit.
7. Read the instruction and service manuals. A thorough understanding of
the unit is the best approach. If ever in doubt
authorized repair center for assistance.
Section Two
consult the factory or an
2 - 5