Repair of frequency converter Fuji Electric Ltd, Frenic MEGA series 5.5kW

INTRODUCTION:

Fuji Electric Ltd Frequency Inverter Service, Frenic MEGA Series 5.5kW

A series of very powerful and compact frequency converters is the FRENIC MEGA series from the Japanese manufacturer Fuji Electric Ltd. They are challenging to service due to their compact design and the need for highly precise electronic components, which have very tight tolerances.

PROBLEM:

A specific device failed the diode test. Its main power IGBT module was completely short-circuited.

SOLUTION:

When replacing the IGBT module, it was observed that the TLP421 optocoupler, along with its external diode, was also damaged. Both were replaced with a generic PC817.

Later, it was found that the SMPS network (which provides stable 5, 12, and 24 VDC outputs) was also damaged and nonfunctional. The SMPS chip FA13844 was completely destroyed. Although this chip is pin-compatible with the widely known UC3844, it must not be replaced with it. The original FA13844 must always be used, as the excitation current differs significantly. FA13844 can be excited with just 30 uA.

When testing the device using a PC, it is important to set the parameters for the smallest possible motor, which can often use default values. This allows even 30 kW devices to be tested with a small 2.2 kW test motor.

TESTING A SERVICED DEVICE