Allen Bradley 1391 AC Controller

Allen Bradley 1391 Drive Fault Code Break Down – What They Mean, Causes, How to Fix

The 1391 Series Allen Bradley drives are still in use on many machines throughout industries, especially automotive, aerospace, food production, wood products and conveyor-type systems.  A stout servo drive system, the 1391 comes in both analog and digital.  Here, we will look at the analog side, but it’s meanings are the same in digital.  A digital 1391 gives you the auto-tune, which sets the parameters with the servo motors, whereas analog has the user manually tweaking dials, dip switches and jumpers by hand, to achieve the optimal running performance of the machine’s drive-motor system.

1391 drives display their faults using a simple LED strip to signify each one: 4 red lights (Hard faults that stop operation), 2 yellow lights that tells you there is an error (soft fault) but will continue to run.  Finally, 2 green lights that signify that the drive is ready and  run enable.  Here are the faults and what they mean, what the typical causes are, and how to troubleshoot and repair.

(WARNING: This drive contains stored energy devices.  To avoid electrical shock, verify that all voltage on the capacitors has been discharged before attempting to service, repair or remove this unit.)

Allen Bradley 1391 Series

The fault LED’s on the 1391 Series Allen Bradley Controller.  Each one explained below.

Over-Temperature – (Red)

Meaning: The controller contains a thermal switch on the heat sink which senses the power transistor temperature.  If the temperature is exceeded this LED will illuminate.

Possible cause(s): The logic supply circuits have malfunctioned or the AC input is incorrectly wired.  If the heat sink thermal has tripped, 1 or more of the following may have occurred:

  1. The cabinet temperature is too high
  2. The cabinet cooling system, fan or AC unit, is malfunctioning, possibly due to prolonged contamination
  3. Contamination of main electrical board inside drive saturated with debris
  4. Airflow to the unit is blocked or limited.

The Fix:  Getting the cabinet cooled by servicing AC system or fans; cleaning system of contamination or debris.  But, if the over temperature that is causing damage due to coating multiple components with contamination inside the drive, this will rapidly degrade and cause them to act differently then intended.  The coating will also hold in heat and cause failure.  Everything internal in the drive is susceptible to damage from overheating once contamination is detected.  Everything from contactor coils, outputs, sensitive electronic boards, can become heat-fatigued and cause them to have different characteristics. When this happens, you may want to have your 1391 serviced by a professional.

Power Fault – (Red)

Meaning:  The power coming in (line voltage) has either malfunctioned or failed by exceeding a fixed level (greater than 300% of the controller rating; or the power circuitry inside unit has failed.

Possible Cause(s):  Typically the line/high voltage jumps up or “spikes” causing your internal circuits (power transistor) to malfunction.  A power outage can also cause damage as when it turns back on, it surges;  Normal aging can also be a cause as the circuits ‘think’ there is a problem.  Other possibilities include:

  1. Shorted Load
  2. Excessive winding to case motor capacitance

The Fix:  There is a small window to correct the incoming voltage when a power fault occurs to ‘save’ the drive from internal damage. Otherwise, your 1391 will need to be serviced.  Aged components will need to be replaced as well.

Control Power – (Red)

Meaning:  If the logic supply (low voltage) rises or drops 10% or more from its normal value, a fault occurs.  This weakens the components over time.

Possible Causes:  You have 2 sets of power coming in, your low and your high, your low voltage is the control power.  This is for powering the ‘brains’ of the drive, which is the mother board.  With power fluctuations that can happen inside a facility, it can keep your drive from running optimally and over time damaging your circuits in your logic board.  You are either ‘starving’ it or ‘flooding’ it with excess power, making it work harder.

  1. The input line voltage is low or high (inconsistent)
  2. The transformer auxiliary logic supply
  3. The logic supply circuits have malfunctioned, sometimes due to normal aging

The Fix: Similar to the power fault above, there is a small window to make adjustments and ‘save’ the drive from internal damage.  Service to unit is recommended.  If you catch it early, minimal repairs are necessary.

Over-Voltage  – (Red)

Meaning: The DC Power Bus is continuously monitored.  If it exceeds a preset level a fault is sensed, the power supply is disabled.

Possible Causes:  The logic supply circuits (in the breaking circuit) have malfunctioned or the AC input is incorrectly wired.  The power bus voltage has exceeded 405V DC.  There is then no where to put the excess voltage and this can damage the rest of the main board.

  1. The logic board is malfunctioning and incorrectly sensing the bus voltage.
  2. A vertical axis with insufficient counterbalancing is overdriving the servo motor and causing excessive energy to be returned to the power supply bus.
  3. The system inertia is too high causing excessive energy to be returned to the power supply bus.
  4. The input line voltage exceeds the maximum controller input voltage rating.
  5. The position controller acceleration/deceleration rate is incorrectly set.
  6. The shunt regulator or transistor has malfunctioned.
  7. Shunt regulator fuse has blown.
  8. Shunt regulator resistor not connected to controller.

The Fix: You can try and change the shunt regulator fuse and start there.  If that does not solve the problem then your drive needs service as the over-voltage has possibly damaged other area’s on the main board.

Undervoltage – (Yellow)

Meaning:  Usually means you are not getting the proper line voltage power in.

Possible Causes:  The power bus voltage has dropped below a preset DC value:

  1. The power contactor has not energized or has dropped out.
  2. The input line voltage is low.
  3. The shunt regulator circuit has malfunctioned and is placing the shunt resistor across the power bus.
  4. The power bus capacitor has malfunctioned.
  5. The circuit breaker has tripped.
  6. The three-phase input line is open.
  7. The transformer is providing the incorrect line voltage or has malfunctioned.

The Fix:  The breaker on top may be off – needs to be on.  Or, somewhere else in the cabinet may have breakers that are off or tripped; Sometimes, the monitoring circuit can have components that have failed which will need service.  More likely, probably not an internal problem though.

Current Foldback – (Yellow)

Meaning:  When the current foldback circuitry is operating.

Possible Cause:  This is typically in the settings of your drive.  Here are known issues:

  1. The acceleration/deceleration command from the position controller is requiring peak current for an excessive amount of time.
  2. The gain pot is set too high causing excessive peak currents.
  3. The machine friction, inertial load and/or viscous loading is excessive.
  4. The servo motor has been improperly sized.
  5. A short circuit exists across the controller output terminals.
1391 Allen Bradley Drives

Manually tweaking the settings using dip switches, knobs, and jumpers on a 1391 Allen Bradley controller.

The Fix:  All of the adjustments can be made under the top cover on the main board.  If you look at the board, there are some switches and knobs built in.  Current limit, gain, motor code settings can be tweeked by a series of dip switches, jumpers, knobs – if you don’t have everything set the correct way you will go into current foldback fault.  By setting these into the correct manner, you should be run enabled.  They can, however, be triggered falsely, by a failed IC or component, but usually it’s just an adjustment to correct this.

Run Enable – (Green)

Meaning:     The application of an Enable signal by the machine position controller will cause this to illuminate.

Possible Causes:  When this is NOT illuminated:

  1. The position controller has not enabled the controller.
  2. The Enable wiring to the controller is open.
  3. The position controller Enable relay/switch has malfunctioned.
  4. The position controller has detected a machine system malfunctioned that will not allow the controllers to be enabled.
  5. Power has not been applied to input transformer.
  6. The logic supply circuits have malfunctioned (fuse blown) or the AC input is incorrectly wired.

Enabled LED is illuminated, but Controller does not enable:

  1. A controller malfunction has occuredbut is not annunciated by the LED indicators.   Check the status of the drive OK (DROK) relay.
  2. A component malfunction exists in the Enable circuit.
  3. The circuit breaker (MCB) is tripped.
  4. The power contactor has not been energized or has malfunctioned.

The controller logic supplies are not operational:

  1. The controller logic supply fuses are blown.
  2. Logic supply AC voltage is missing
  3. A controller malfunction has occured but is not annunciated by the LED indicators (check the status of the Drive OK contacts)

Drive Ready – (Green)

Meaning:  This LED is continuously illuminated until a system fault occurs.  When Drive Ready LED is NOT illuminated:

  1. System fault has occured.

In conclusion, the 1391 Series Allen Bradley Controller drives have been a stalwart for many years.  A stout, built drive, they are able to take a lot of abuse and are able to be repaired over and over, keeping them in service.  If you have internal damage on your 1391, trust a reputable repair center for thorough evaluation and repair.

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