A second-hand Javelin 2000-600 arrives with no drawings, operating instructions, or PLC documentation, leaving the knife control path unknown. Treat the Allen-Bradley SLC-150 as one hop in that path, not as proof of a communications problem. Follow each command from the field device, through PLC input and logic states, to the output and final actuator.
Where does the control request enter the machine?
Begin at layer one. Identify the device that requests each action: start, stop, knife movement, reset, or any other observed function. Record the device terminals and trace both conductors without assuming their destination. A pushbutton may feed a PLC input, a relay circuit, or another controller interface.
Build a path record before changing wiring or logic:
| Hop | Reading to take | Address or port source | Outcome |
|---|---|---|---|
| Command device | Contact state and control voltage | Terminal markings and wire labels | A changing contact with no electrical state change indicates a field-device or supply problem. |
| PLC input | Terminal voltage and input indication | Installed module labels and recovered program | Voltage changes without an input-state change point to input wiring, common, or hardware. |
| PLC logic | Input, permissive, latch, and output states | Recovered SLC-150 logic |
An input state that stops before the output identifies the blocking logic condition. |
| PLC output | Output indication and switched voltage | Output terminal and program reference | A commanded output with no electrical transition points to output power, common, wiring, or hardware. |
| Final device | Coil voltage, actuator response, and feedback | Device nameplate and traced conductors | Correct voltage without motion moves the investigation beyond the PLC. |
No network interface, node address, or communications port is identified for this installation. Leave those fields marked unknown until physical inspection finds an actual interface. Do not assign an address or configure a protocol merely because the machine contains a PLC.
Does the physical layer carry the request?
Operate the command device and measure at successive terminals. First prove the control-power reference and return path. Then check the device contact, intermediate terminal blocks, PLC input terminal, and input common. A meter reading at the source but not at the next terminal localizes an open conductor, loose connection, failed contact, fuse, or interlock contact.
| Observation | Meaning | Next check |
|---|---|---|
| No control voltage at the command device | The request cannot enter the control path. | Trace the control supply and its protective devices. |
| Voltage changes at the device but not at the PLC terminal | The field path is open or incorrectly terminated. | Trace terminal blocks, connectors, and intermediate contacts. |
| Voltage changes at the PLC terminal but not relative to input common | The reference or common path is wrong or open. | Verify the installed input circuit and common conductor. |
| Correct electrical transition and matching input indication | The physical input path works. | Continue to the PLC logic check. |
Read voltage type and permissible level from the installed hardware labels or documentation obtained for that exact hardware. Do not infer them from the machine model or substitute a convenient test voltage.
Does the SLC-150 recognize the input?
The SLC-150 control path is input state, program evaluation, then output state. Compare the field measurement with the controller indication and, when the correct programming equipment and a valid backup are available, the corresponding program state.
If the terminal voltage changes but the input indication does not, remove program logic from the diagnosis temporarily: examine input power, common wiring, terminal condition, and the input point itself. If the indication changes, follow that input through the recovered program. Document every contact, branch, latch, timer, and output reference encountered; their exact identifiers must come from the program.
Do not edit an undocumented program to force progress. First obtain a backup and record the controller state. A forced or bypassed input can conceal a failed guard, limit switch, pressure condition, or motion feedback and may command the knife unexpectedly.
Which permissive prevents the output command?
When the PLC sees the request but does not command the expected output, inspect the logic path in its evaluated order. The first false series condition or unresolved branch identifies the next field measurement.
| Logic state | Diagnostic meaning | Required action |
|---|---|---|
| Request false | The command never reached the program. | Return to the input path. |
| Request true, permissive false | An interlock or feedback blocks the command. | Locate that field device and verify its actual state electrically and mechanically. |
| All conditions true, output state false | The branch, latch, sequence, or program mode needs examination. | Trace every instruction controlling the output and check for another instruction writing the same destination. |
| Output state true | The PLC has completed its decision. | Move to the electrical output circuit. |
Record timing from observation instead of guessing it. Note when the request becomes true, when each permissive changes, how long the output remains commanded, and when feedback returns. Compare those readings with timer values recovered from the program and device data obtained for the installed components.
Does the output reach the knife actuator?
With the output state true, measure from the PLC output terminal to the correct circuit reference. Also prove the output supply and common; an illuminated output indication does not prove that external power reaches the load.
If voltage is absent at the output terminal, examine the output supply, fuse, common, terminal, and output point. If voltage exists at the PLC but not at the final device, trace intermediate relays, terminals, connectors, and conductors. If the correct voltage reaches the device but the mechanism does not respond, inspect the coil or actuator, mechanical binding, air or hydraulic energy where fitted, and device feedback. Read the required voltage, pressure, and ratings from the installed nameplates rather than assigning generic values.
A single-knife slitter also requires a mechanical inspection before powered testing. Confirm the knife is secured, the travel path is clear, and the mechanism can occupy its expected positions under the machine's approved isolation procedure.
How do you reconstruct and verify the resolving branch?
- Photograph the cabinet, controller, modules, terminal strips, field devices, wire labels, and nameplates before disconnecting anything.
- Create an I/O list containing the physical terminal, observed PLC state, program reference, field device, normal state, and controlled function.
- Trace the failed command from its field contact to the
SLC-150input. Repair only the open, incorrect, or failed element identified by measurement. - If the input works, trace the program until the first false permissive. Test that permissive at its field device and restore the underlying condition; do not leave a bypass or force in service.
- If the PLC output becomes true, trace switched power through any intermediate device to the actuator. Repair the first point where the expected electrical state disappears.
- Remove temporary test connections and forces, restore guards and normal isolation boundaries, and update the reconstructed drawings and I/O list.
- Test each command while observing field input, PLC input, permissives, PLC output, actuator response, and feedback in sequence. Record measured timing and final normal states.
FAQ
How do I troubleshoot a Javelin 2000-600 with no manual?
Trace one function at a time from command device to PLC input, logic condition, PLC output, and actuator. Build the terminal and I/O record from measurements, installed labels, and the recovered SLC-150 program.
How do I tell whether the SLC-150 input is faulty?
Measure the signal at the input terminal relative to its common and compare it with the controller input indication. A correct transition at the terminal with no state change directs the check to the common, input wiring, terminal, or input point.
How do I find which interlock blocks the knife command?
Follow the requested output backward through the PLC logic and identify the first false series condition or unresolved branch. Then measure the corresponding field device instead of bypassing it.
How do I verify the repair before returning the slitter to service?
Remove all forces and temporary connections, restore guarding, then repeat the command while observing the field input, PLC input, every permissive, PLC output, actuator motion, and final feedback. Accept the repair only when the complete sequence repeats with the documented normal states and measured timing.