MTZ 952 - Page 38

Controls and Instrumentation
MTZ series 900
7
The identification of the block pins is given in Table 4.
Table 4
Pin
Identification
1
to the terminal “–“
2
to the power supply unit “+12В”
3
to the board output “Parameter selection”
4
to the board output “Parameter value”
5
to the board output “Mode”
6
to the speed sensor BV2 (left wheel)
7
to the speed sensor BV1 (right wheel)
8
to the phase winding “W” of the alternator
9
to the instrument backlight lamps
1.5. Tachospeedometer diagnostics and troubleshooting
1. No instrument backlight:
Check the power supply wire connected to the pin “9” of the 9-contact block of the in-
strument (Fig. 3) – check if the backlight lamps are intact.
2. Jerking and jumps of the pointer of the engine rotational speed indicator over
the dial: poor contact on the alternator terminal and, therefore, poor signal from the
phase winding of the alternator. Repair.
3. Jerking of the pointer and understating the reading of the engine rotational
speed:
- Check and adjust the tension of the alternator driving belt.
4. Over- or understated readings of the engine and PTO’s rotational speeds (with
the normal movement of the pointer):
- Check the correctness of programming the instrument according to the engine make
(parameter “D”): (see item 1.3);
5. The counter of astronomical hours of the engine running fails to accumulate the
operating time: Check the connection of the wire to the contact “8” of the instrument
block and the presence of the frequency signal from the phase winding of the alternator.
6. Over- or understated readings of the tractor speed:
- Check the correctness of the instrument programming according to the rolling radius of
the rear wheels (Rk) (see item 1.3);
- Check the correctness of the programming according to the number of teeth of the half-
axle pinion (Z) (see item 1.3).
7. No readings of the tractor motion speed: Check the presence of signals from both
the speed sensors (BV1, BV2).
8. The readings “02…07” km/h appear on the instrument indicator when the tractor
is moving:
- the numbers “02…07” and, 12 seconds later, “0” appear from the right side of the scale
– no signal from the right speed sensor (BV1).
- the numbers “02…07” and then “0” appear from the left side of the scale – no signal
from the left speed sensor (BV2).