264
Model Code Page
31. Σ --- p o w e r s y s t e m
1. 10. 1999
8750, 8950 313 6
1. 6. 1999
3. Fault tracing, adjustments and repairs
If the Sigma Power - system has malfunctions, the function is checked in the following order:A. Checking function with the aid
o f t h e E T B --- l i g h t
B. Checking function and sensor adjustment with the aid of the Ac display.
C. Fault tracing by measuring voltages
D. Checking and adjustment of the sensors with the aid of Fluke123 oscilloscope (if necessary)
A. Checking function with the aid of the ETB ---light
The ETB light in the dashboard indicates the engagement of the system and it also shows by flashing possible faults which
are found by the control unit.
ETB -light status Description Possible reasons
Off
1
) Engine lower output range on (valve Y13 unener-
gised)
On (when great PTO
loading)
Engine higher output range on (valve Y13 is ener-
gised)
On (although no loading
in PTO) or flashes ran-
dom.
Faulty function --- Sensor adjustment incorrect, control
unit faulty
Flashes
2son*)/0,5soff
*) New control units: 1
sec on.
--- Solenoid valve Y13 control is not engaged (e.g.
short circuit)
--- or not load in the valve electric circuit
--- Valve solenoid burnt, wire short circuit,
earth fault
--- Valve solenoid faulty, wire broken,
poor connections, valve connector dis-
connected
Flashes
0,5 s on / 0,5 s off
--- No signal from sensors B4 or B5
1
)
2
)
3
) --- Poor contacts in wires/connectors,
sensor adjustment incorrect, faulty sen-
sor
Note!
1
) If the signal from both sensors is lacking, the ETB -light does not flash or glow. In this case the adjustment and volt-
ages of both sensors must be checked.
Note!
2
) Versions 1.0 and 1.1: The ETB light does not show, signal of which of the two sensors is lacking. This can be
cleared up by disconnecting the engine sensor B4 connector and by starting the engine again. If the ETB -light again flashes
(0,5s / 0,5s), the fault lies in the engine sensor B4 circuit. If the ETB light goes out, the fault lies in the PTO sensor B5 circuit.
Note!
3
) Versions 2.0 and 3.0: Flashes twice in time mentioned above, after which there is a pause of 1,5 sec=engine sen-
sor faulty. Flashes three times , after which there is a pause of 1,5 sec.=PTO sensor faulty.
B. Checking function and adjusting sen-
sors with the aid of Ac---display
Instructions on instrument, see page 331/1.
The Ac---display shows in percentage, how big part of the
tractor PTO output is transmitted by the PTO unit, when the
PTO is engaged. On the ground of the display reading the
function of the Sigma can be investigated during driving.
1. Start the engine (PTO disengaged), let it runt at the low
idling speed for a while (about 20 s), now the control unit
has made the calibration of the 0 ---mode. Set the instru-
ment so that it shows the Ac ---reading (Agrodata -instru-
ment). Run the engine up to max revs (warm the engine
first). If the Ac ---display shows other digits as zero, this indi-
cates that the sensor adjustment is incorrect.
2. If the sensor adjustment must be done, it is better to start
the work with the foremost sensor. Turn the sensor in the
flywheel housing fully home (not at the notch), and unscrew
then 1/2---2/3 turn (thread M18x1,5), the clearance is now
0,75---1,1 mm (locking nut; spanner width 27 mm). If the
foremost sensor impulse wheel is located in the front end of
the crankshaft (---H02430), the clearance is easy to check
and adjust to 0,8 mm.
3. Run the engine as in paragraph 1. If the situation did not
change, the rear sensor must be adjusted (engine in the
running during adjustment). Unscrew the locking nut (1000;
spanner width 22 mm, 1000/540 E; 27 mm) and turn the
sensor outwards, and test whether the fault disappeared or
the situation changed.
With the adjustment is seek situation, in which percentage
readings do not appear in the Ac---display, and the ETB---
light does not flash in any revolution range. The rear sensor
clearance can be checked, if needed, through the hole for
the free return oil connection for the auxiliary hydraulics.
4. Start the engine and let it run at the low idling speed
about 20 s. Engage PTO, run the engine up to max. revs.
Small readings (1---3 %) can be visible in the Ac---display
when accelerating. Set the engine revs to 1800---2200, and
pull at the hydraulic valve block lever. In the Ac---display
there must be 10---25 % (shaft twist caused by hydraulic
pump, depends on oil temperature and revs).
If the Sigma still has malfunctions after adjusting sensors,
the possible fault is seek by measuring internal voltages of
the system.
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