I was assigned to repair a Siemens 6SC130-0FE00 SERVO AMPLIFIER CARD. I tested all the power transistors with my DMM's Diode Test Mode. The power transistors did not test shorted or leaky. I then tested the diodes with my DMM. I found two leaky diodes,part number SB130 (labeled V123 and V622 on the PCB). I replaced the diodes to make the repair.

I then had to build a test set to power up the Servo Amplifier Card, and test its ability to run a motor. The main challenge with powering up the Servo Amplifier Card was with the switching power supply circuit. The Servo Amplifier Card only has the Switching Transformer whose primary winding is connected to ribbon connector X211. The switching circuitry to drive the primary winding is located on another card that I did not have.

The primary winding resistance read less than one ohm. This meant that if my switching circuit were to lock up in the full on mode, the chances were very high that the primary winding would be damaged. Thus great care had to be made in choosing a MOSFET that could handle the high voltage and current to safely switch the primary winding.

Once I had my switching circuit built, I had to experiment with the frequency and high voltage until I had good logic and analog voltages on the card. From the age of the card, I knew that the ballpark frequency would be around 15kHz to 25kHz. The best frequency for this card was 16.7kHz. My high voltage for the switching circuit was created from an external bridge recifier and two high voltage electrolytic capacitors wired in series. I used a VARIAC (Variable Transformer) connected to the AC input of the bridge rectifier to adjust the DC Voltage across the high voltage capacitors.

Now that I was able to power up the Servo Amplifier Card, the next step was to build a way to fire the power transistor outputs to the motor. The Servo Amplifier Card has six opto-coupled inputs at the ribbon connector X211, that turn on the the power transistor stages. Three inputs are used to fire the "High Side" power transistors, and three inputs are used to fire the three "Low Side" power transistors. The motor's rotation is dependent upon how these six inputs are sequenced.

I knew that I did not have to fire each power transistor output stage in this sequence. I only needed to see that a stage fired to know that it was good. So I connected six push button switches to the correct input pins of ribbon connector X211. The only caution being that I absolutely would not push at the same time the button for the "High Side" and "Low Side" power transistor stages of the same output. If I were to do so, the high current of the bus voltage connected to the P200 and M200 terminals would shoot through that power transistor stage and destroy it.

To make the motor bus voltage, I connected another bridge rectifier and two high voltage electrolytic capacitors wired in series to the terminals P200 and M200. Again, I used another VARIAC (Variable Transformer) connected to the AC input of the bridge rectifier to adjust the DC Voltage across the high voltage capacitors. I then pushed only one of the buttons to fire a single power transistor stage. I viewed the output change with an oscilloscope. I then performed the same test with the other five power transistor stages. All the six transistor power outputs turned on correctly.