Relay Boards; To Replace A Relay; To Replace A Circuit Breaker; Service - Komatsu 930E-2 Shop Manual

RELAY BOARDS

The Electrical Interface Cabinet contains six relay
boards to provide control for many of the 24VDC
circuits. Two types of boards are used; those contain-
ing circuit breakers in addition to 24VDC relays and a
PC board for special functions, and a second type
containing relays only.
All relays are interchangeable. The circuit breakers are
interchangeable, providing the circuit breaker capacity
is the same. Do not interchange or replace any
circuit breaker with one of a different capacity than
specified for the circuit. Serious damage or a fire may
result if the wrong capacity breaker is used.
RELAY BOARDS RB1, RB2, RB3, RB4, RB5
Each relay board of this type is equipped with five green
lights (9, Figure 3-6) and one red light (7). Four green
lights are labeled K1, K2, K3, or K4. These lights will be
"ON" only when that particular control circuit has been
switched "ON" and the relay coil is being energized.
The light will not turn on if the relay board does not
receive the 24 volt signal to turn "ON" a component.
Each relay board has a 5th green light that has a
different function on each board.
The red "Breaker Open" light (if "ON") indicates that a
circuit breaker (on that relay board) is in the "OFF"
position. A light on the overhead display panel will also
illuminate, informing the operator that a circuit breaker
is in the "OFF" position. The red breaker open light will
turn "ON" whenever there is a voltage difference
across the two terminals of a circuit breaker.
If a control switch has been turned "ON" and a green
(K) light is "ON", but that component is not operating,
check the following on the relay board for that circuit:
Check for a circuit breaker that is in the "OFF"
position or a red (breaker open) light is "ON". If
a circuit breaker is "OFF", turn it "ON". Check
operation of component. If it trips again, check
the wiring or component for cause of overload.
The contacts inside the relay may not be closing,
or the contacts may be open, preventing an
electrical connection. Swap relays and check
again. Replace defective relays.
Check the wiring and all of the connections be-
tween the relay board and the component for an
"open" circuit.
Defective component. Replace component.
Poor ground at the component. Repair the
ground connection.
D03019 04/01

Service

To replace a relay:

NOTE: The relays are labelled to identify the applicable
circuits and components Also, refer to the Circuit
Breaker Chart at the end of this Section.
1. Remove one screw (10, Figure 3-6) holding the
crossbar in place and loosen the other screw.
2. Swing crossbar away.
3. Gently wiggle and pull outward to remove relay
(11).
4. Line up tabs and install new relay.
5. Place crossbar in original position and install
screw (10) that was removed and tighten both
screws.

To replace a circuit breaker:

NOTE: Always replace a circuit breaker with one of the
same amperage capacity as the one being removed.
1. Place battery disconnect switches in the "OFF"
position.
2. Unplug all wiring harness(s) from relay board.
Remove four relay mounting screws and remove
relay board from truck.
3. Remove four hold down screws (3) (one in each
corner) in circuit breaker cover plate and all circuit
breaker screws. Remove cover plate from circuit
breakers.
4. Remove nuts and star washer from back side of
circuit board that holds the breaker in place.
5. Lift out circuit breaker. Retain flat washers that
were between inner circuit breaker nut and relay
board.
6. Install one nut and two flat washers to each pole
on the circuit breaker. Nuts must be adjusted to
the same height as on the other circuit breakers.
This is necessary so when cover plate is installed,
it will not press circuit breaker into, or pull up on,
the circuit board. Install new circuit breaker of the
same capacity rating as the one removed.
7. Install star washer and nut to circuit breaker poles
(on the back side) and tighten nuts.
8. Install cover plate and all screws removed during
disassembly.
24VDC System Components D3-9