GP20 Granulator & Shredder Interlock Faults

Common Error Messages

The following error messages may appear when a safety interlock is not in a safe state.

Granulator messages

“Side door is not secure”
Top safety interlock open
Bottom safety interlock open

Shredder message

“Linked machine not ready”

In most cases, the shredder error is a secondary fault caused by a safety interlock issue on the granulator. The granulator must be in a safe state before either machine can operate.

1. System Architecture and Error Logic

The shredder and granulator share a connected safety interlock system. Both machines must report a safe state before operation is allowed.

If any safety interlock on the granulator is open (side door, top interlock, or bottom interlock), the shredder will display:

“Linked machine not ready”

Therefore, always resolve the granulator safety alarm first before troubleshooting the shredder.

2. Physical Inspection & Mechanical Alignment

Before testing electrical components, verify that the mechanical parts are correctly aligned and fully closed.

Door closure verification

Ensure all toggle latches are fully engaged.
The door must sit flush against the frame with no visible gaps.

Mechanical play

Pull gently on the door to check for movement.
If the door shifts, the hinges or latch keepers may need adjustment so the actuator properly engages the safety switch.

Obstruction check

Inspect for debris in:

door seals
hinge areas
latch points

Granulated material can prevent the door from closing completely and activating the safety switch.

3. Safety Switch Diagnostics

The safety interlock switches are mechanical components and may fail due to wear, misalignment, or debris.

Visual inspection

Power off the machine and check for:
- cracked switch housing
- bent actuator
- loose mounting screws
Manual actuation test

Manually press the switch actuator.

Expected behavior:
- A clear tactile “click”
- The switch returns immediately to its original position.
If the switch:
- feels soft or “mushy”
- does not click
- does not spring back
the internal contacts may be damaged or contaminated.

If the door is fully closed but the alarm remains active, the switch may be misaligned or electrically open.

4. Electrical Continuity Testing (DB25 Interface)

To determine whether the issue is caused by the switch, cable, or controller, perform a continuity test using the DB25 connector located on the granulator head.

Important

For this test, all interlocks must be in the safe state:

side door closed
hopper installed
output bin installed
machines properly stacked

Step A — Preparation

Disconnect the machine from the power source.
Set the multimeter to continuity (Ω) mode.
Disconnect the DB25 cable from the granulator head.

Step B — Pinout Reference

Measure continuity on the granulator-side connector.

Interlock	DB25 Pins	Expected State
Bottom interlock	1 & 2	Continuity (<1 Ω)
Granulator door	2 & 3	Continuity (<1 Ω)
Top interlock	3 & 4	Continuity (<1 Ω)

If continuity is not present, the issue is likely with the switch or its alignment.

Step C — Cable Integrity Test

If the switches show correct continuity at the granulator connector, test the DB25 cable.

Connect the DB25 cable to the granulator.
Leave the cable unplugged from the control box.
Measure continuity at the control-box end of the cable.

Failure indicators

Continuity present at the granulator connector but not at the cable end.

This indicates a damaged cable or broken wire inside the cable.

5. Control Box Assessment

If continuity is present through:

the safety switches
the granulator connector
the DB25 cable

but the error persists, the issue may be inside the control box.

In this case, contact technical support for further diagnostics.