Galil ICM-1100 Amplifier Board Modifications

 

 

Theory;

 

The sudden loss of AC power to the DEIMOS motor controllers results in a runaway condition on the stage motors. These thirty or forty revolutions of uncontrolled motion of the motors could cause severe damage to the equipment installed on the DEIMOS stages.

 

The problem is caused by the almost instant loss of the five-volt (logic) supply, while the motor driver supply (28volts) remains on for almost another two seconds. The active-low motor driver inhibit is pulled high by the pull-up resistors and the motors are enabled to drive without control during those final two seconds.

 

The solution is to invert the logic (inhibit is now high) and use pull-ups that derive their power from the 28-volt supply to stop the motors. This involves replacing U1, a 7407 open-collector buffer, with a 7406 inverting open-collector buffer. A 12-volt, 3-terminal regulator is used to generate the 12-volt pull-up voltage from the 28-volt amplifier supply.

 

Parts Required per Amplifier Board:

 

  1. Remove the amplifier circuit board from the frame (6 button head hex screws).

    2.  

  2. Carefully remove the 4 amplifier modules from the bottom of the board, noting the position of pin 1.

    3.  

  3. DM7406 Hex Inverting Buffer with High Voltage Open Collector (1 ea.)

    4.  

  4. LM78M12CT (LM340T12 or LM341T12…) Series 3-Terminal +12 Volt Positive Voltage Regulator

    5.  

  5. 6-Pin Resistor Network (SIP) 4.7K Ohm (1 ea.)

    6.  

  6. 2 feet of #24 solid conductor hook-up wire

 

Procedure:

 

  1. Cut the traces to the Inhibit/Bar inputs of each of the four amplifiers (Pin 14). These are connected to pins 3, 7, 11 and 15 of the 104-pin screw terminal strip. You will need access to the underside of the ICM-1100 board to do this.

    2.  

  2. Cut the connection between the 5 volt supply and pin 1 (Marked 5V) on the resistor pack socket RP1

    3.  

  3. Solder the 3-terminal regulator in place on top of the prototype section of the circuit board with the pins projecting through to the underside.

    4.  

  4. On the underside, connect the middle pin of the regulator to the nearby ground.

    5.  

  5. Connect the input pin (the left pin looking from the front of the regulator) to the under side of the 28 volt supply terminal (mid board).

    6.  

  6. Connect the remaining regulator pin (output) to pin 1 (Marked 5V) of the resistor pack socket RP1. This completes the wiring required on the underside of the board.

    7.  

  7. On the top of the board, cut away the RTV from pin 12 or each of the four amplifiers.

    8.  

  8. Connect pin 12 of :

 

 

 

  1. Replace the 7407 (U1) with a 7406

    2.  

  2. Install a 4.7K, 6-pin SIP in the socket RP1. Pin-1 (common) should be placed in the slot that was labeled 5V. (It is now 12 volts. Ink over the "5V" label to avoid confusion in the future.)

    3.  

  3. Replace the RTV that was removed for soldering and re-assemble the unit.