Repairing Ac drive/ VFD/ Inverter.

How to repair a Ac drive? How to Repair VVVF Drive? How to test AC drive? How to test hardware of AC drive.

We have seen many customers face a problem to find a service center where most of drives are repaired. If they find one right place it is very difficult that they get repaired in time. Most of them take so long to rectify the problem.

We will help you to rectify basic problem with VFD or AC drive at your end so that you can take fast action and save time in repairing a VFD.

Let have a look at basic VFD hardware block diagram.



Basically VSD (Ac drive is divided into three main parts

  1. Rectifier circuit.
  2. DC bus capacitors.
  3. IGBT rectifier unit.

Rectifier unit does the function of rectifying AC mains input voltage to rippled DC voltage. This rippled DC voltage is then filtered with LC Filter.

This dc voltage is stored in DC bus Capacitors bank. If the input voltage VFD is 440VAC than with thumb rule DC bus voltage would be approx. 1.5 times that is 660VDC.

Third unit consists of IGBT rectifier. Which converts DC bus voltage to AC (PWM). Output frequency is controlled gates of IGBT. A Microcontroller based modules controllers the carrier frequency and Output frequency of IGBT inverter.

If your drive is faulty and not working as per application and your needs you can have a cold test of VFD. Cold testing means testing of above three parts.

When you power on drive please check DC voltage at Plus (+) and Minus (-) Terminals of VFD With multimeter on VDC @ max selection. As Discussed above DC voltage should be approximately equal to 1.5 times of input ac voltage.

If It shows correct reading than you have the futher testing of IGBT and rectifier. For this you should adjust you ditgital multi meter to Diode testing. (Note: don’t use Ohms meter to test this, as it may give you wrong readings.

Than do the following testing in a chart.


In Above chart if you found any reading other than expected results than you can understand that particular IGBT or Diode is Fault.

After testing if you can repair or replace the faulty part you can do it of your own. Or you can send it to us we can fix it for you.

You must do above test before sending a drive for repairing, and we bet you will save a lots of money.

If you all this three parts are functioning properly than you need to send it to us for further diagnosis of VFD. The fault might be in control card, SMPS, Connectors, ETC.


We can repair AC drives VFD from various brands Such as AB ( Allen Bradley), ABB, CG (Crompton greaves), Danfoss, Delta, Emerson, Fuji, Gefran, Hitachi, Innovance, Inova, INVT, LG, Mitsubushi, Panasonic, Powtran, Schnieder Altivar, Telemechqnic, Siemens, Sunfar, Toshiba, Yasakawa, Teco, Monarch,

We give you analysis report and budgetary offer in one working day. We charge minimum charges than anyone else. We understand your breakdown time, and we try to minimize as much as possible.

If you have any other brand apart from mentioned above. Please let us know we will be glad to serve you.

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