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Centroid DC Servo Drive Preventive Maintenance

The logic power supply connections on Centroid SERVO1 and QUADDRV DC servo amplifiers need to be cleaned periodically.

These drives were used in all DC M10, M20, M40/50/60, M39 and M400 controls, plus equivalent lathe controls, from 1993 through 2002.

Symptoms of a system which needs to have the servo logic supply connections cleaned include:

Typical M40 cabinet Shown at right is a typical M40 control cabinet. The servo drive is in the lower right, mounted to the side of the cabinet by its aluminum heat sink.

Note: if you have a Revolution mill or a Magnum/Phoenix router table, you will have this same servo drive unit, but your cabinet layout will probably be very different.

There is a small switching power supply mounted on the back of the servo drive. In earlier controls (ca. 1993-1999) it is a Toko brand supply with a brown circuit board. In later controls (ca. 1999-2002) it is a Cosel brand supply with a green circuit board.

The switching power supply receives 110VAC power on one end, through black, white and green wires. It sends out +5VDC, +12VDC and -12VDC power to the front side of the servo drive through various colored wires: most commonly red, black, white and green. This DC power is connected to the servo drive using four positions of a white six-position Molex connector, located near the status LEDs on the left edge of the drive.

Every 2-3 years you should power off the control, open the cabinet, and use electronic contact cleaner to clean the servo drive logic power connections. Most important is to clean both ends of the short DC logic power cable from the switching power supply to the front of the drive.

The front connection is clearly visible and easy enough to reach. The other end, where it plugs into the switching power supply, is somewhat harder to reach. A mirror can be helpful. With Toko supplies, the back side connection is usually a brown Waldom connector, very similar to the limit switch connectors on the drive and PLC. With Cosel power supplies it is usually a white connector, possibly with a thumb latch on it.

On some later Toko-supply systems, Centroid soldered the wires directly to the pins and did away with the brown plug. If you look in the back and just see black heat shrink tubing where the wires meet the board, then you have soldered connections and should leave that end alone.

As long as you are in the cabinet with a can of contact cleaner, you should also treat the AC-side connection to the servo drive logic power supply; both ends of the limit switch cable; and both ends of the drive fault cable.

As noted above, the AC supply to the servo logic power supply plugs into the Toko or Cosel unit on the back of the drive. Toko connections could again be brown press-on connctors, or directly soldered. Cosel connections will be a white plug with a thumb latch.

The limit switch cable plugs in higher up the left edge of the drive, and is a 8-position or 10-position brown Waldom plug. On later M40/M50/M60 controls and most M400 controls, it leads to the top edge of the RTK2 PLC unit, next to the three optical fibers. On M39 controls the limit switch cable leads to screw terminals on the 15/15 PLC unit.

The drive fault cable plugs into the servo drive just below the logic power connection, via a 4-position brown Waldom plug. Again, on controls using the RTK2 PLC unit it plugs in to the top edge next to the limit switch cable, and on controls using the 15/15 PLC unit it is broken out to various screw terminals.

Clean the limit and fault cable connections to the servo drive. If you have a control with the RTK2 unit, clean the connections to the RTK2. If you have the 15/15 PLC, it is not necessary to clean the PLC ends of these cables.

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Copyright © 2007 Marc Leonard
Last updated 06-Sep-2007 MBL