An REA Technologies,Inc. Field Technician was called out to troubleshoot a Ward 50 Inch Flexo machine at a customer's site. The customer wanted the machine repaired before the sun came up on the next day. The Field Technician found that the Indramat Servo Drive (Model Number TDM3.2-020-300-W0) would not properly rotate the motor when the drive was enabled. The customer had a spare Indramat Servo Drive of the same model. But when the Field Technician installed this spare Servo Drive, the +24/+-15 Power Good LED did not illuminate. Indicating that there was a problem with the power supply. The first Servo Drive's Power Good LED illuminated, so the problem was not with the Indramat Power Supply Unit.
The field technician brought both Servo Drives back to our shop for repair. He also brought the Motor, so that we could test the Servo Drive after the repairs were made.
I tested the Transistor Power Module, of the first Servo Drive, with my DMM Diode Test Mode. I found that the "V" Output stage was open. The "U" and "W" stages were intact. Also the driver transistors for the "V" Firing Channels were shorted. This Servo Drive was going to take new parts and much time to repair, so I concentrated my efforts on the second Servo Drive.
The Transistor Power Module of the second Servo Drive was good. I didn't have an Indramat Power Supply Unit, but I knew from previously working on Indramat Servo Drives, that I could use external power supplies to make the +/-15VDC and +24VDC for the Servo Drive. I could also make the +300VDC Bus Voltage from a Variable transformer, a bridge rectifier module, and high voltage bus capacitors.
I turned on the external power supplies, and the +24/+-15 Power Good LED was not illuminated, just as the Field Technician saw out at the customer's site. I measured + and - 15VDC good on the Control PCB. But then I noticed that the ammeter on my +24VDC Power Supply was registering 1.5 amps of current draw. One of the functions of the +24VDC Input to the Indramat Servo Drive is to provide the voltage to a secondary power supply on the Power PCB. This secondary power supply in the Servo Drive creates the isolated firing channel voltages on the Power PCB.
I removed the Power PCB so that I could replace the electrolytic capacitors. After removing the capacitors from the Power PCB, I found that four out of six 1000 microfarad, 16V electrolytic capacitors were completely shorted. This explained the abnormally high current draw from my +24VDC power supply.
I replaced all the electrolytic capacitors on the Power PCB and re-assembled the Servo Drive. Afterwards, I powered up the Servo Drive and the +24V/+-15V Power Good LED illuminated. Good Good.
The Field Technician was unable to remove the Drive's Motor cable and Feedback Cable from the machine, so while I was troubleshooting and repairing the second Servo Drive, he was making the cables from wire and connector pins we had on bench stock.
He connected the Motor Power Cable and Feedback Cable to the Servo Drive and Motor. I turned on the Power Supplies to provide the + and - 15VDC and +24VDC. I then turned on the +300VDC Power Supply. I enabled the drive and it ran the Servo Motor good. With the speed potentiometer input to the Servo Drive, I could run the motor CW and CCW with full speed control.
The Field Technician brought the repaired Indramat Servo Drive and Motor back to the customer site for installation in the machine. The Servo Drive performed perfectly. The owner of the machine was very pleased we were able to quickly get it running again.
The customer also wants us to repair the first Servo Drive, so that he can have a good spare.