CUSTOM TRUCK LOAD KING 25-92, Installation Manual

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6.4 Anti-Two-Block Function Overview
The computer supplies a protected positive feed to the Anti-Two-Block switches at the boom/jib head
via the extension reel signal cable, slip-ring, and reeling drum cable. With the Anti-Two-Block weight
hanging freely on the switch, the switch contact is closed and the signal return to the computer is high.
When the weight is lifted by the hook block, the switch contact is opened, and the computer will sense a
low signal input from the A2B signal return.
Since the computer checks the protected feed voltage internally, the system is capable of detecting a
short circuit of the feed (or the ATB signal return when the switch is closed) to the crane chassis. Fault
codes are defined in
FAULT REPORTING AND FAULT CODES
.
Most problems with the ATB circuit may be identified through inspection of cables, switches, and the
reeling drum. Damage to these parts may result in continuous or intermittent A2B alarms.
6.5 Checking the Reeling Drum Cable
The outer braid of the cable carries the Anti Two-Block feed to the switches. If the cable sheath is
damaged, this may cause a short circuit to the boom/chassis and indicate a fault code of “B008” (Refer
to GROUP “B” FAULT CODES ). The same fault code will be indicated if the A2B switch is closed and
the inner core of the cable is shorted to the chassis at some point in the wiring.
1. Carefully inspect the reeling drum cable for wear.
2. Check for signs of damage to the outer sheath of the cable.
3. Check for any signs of severe “kinking” or crushing of the cable.
6.6 Checking the Anti-Two-Block Circuit
Before continuing, ensure the connectors are correctly connected to the A2B switches at the boom
head/jib. This procedure checks the ATB circuit when no power is applied to the circuit, use the
diagram on the following page.
1. Remove the extension reel cover.
2. Disconnect the slip-ring arm from the plug by pulling it away from the center of the reel.
3. Close the A2B switch at the boom head by suspending the weight from it or pulling on the chain.
4. Measure the resistance between TB2-1 & TB2-2 terminal connections on the sensor arm.
5. With the A2B switch closed, the resistance should be less than 300 ohms. If not, inspect the
reel-off cable, A2B switch, and the boom head connectors for an open circuit.
6. Open the A2B switch at the boom head by lifting the weight.
7. Measure the resistance between TB2-1 & TB2-2 terminal connections on the sensor arm.
8. With the A2B switch open, the resistance should be greater than 10,000 ohms. If not, inspect
the reel-off cable, A2B switch, and the boom head connectors for a short circuit.