Cars are equipped with two sound signals: pneumatic, mounted on the cab roof, and electric, consisting of two signals: low and high tone

A noise relay-buzzer is also installed, signaling a decrease in air pressure in the circuits of the brake system and clogging of the air and oil filters of the engine, which is determined by a change in pressure when the filters are clogged.

The scheme for switching on sound devices is shown in fig. 1.

The pneumatic signal is controlled by the button located on the right side of the steering column switch 8.

This button turns on the electro-pneumatic valve, which opens the access of compressed air to the signal.

The signal has two horns: high and low frequency.

When air is supplied to the signals, the vibrators begin to vibrate, making a loud melodic sound.

The electric signal is turned on by the handle. located on the left of the steering column switch (turn signal control knob).

When the handle is lifted up, the RZ relay winding is connected to ground (see Fig. 1, which turns on the sound signals.

Possible malfunctions of the sound alarm system

Pneumatic signal not working

- Fuse No. 7 blown

Replace fuse

- Electrovalve failed

Remove and replace solenoid valve

The air horn makes a wheezing sound

- Low air pressure in the system

Pump air into the system

- Signal vibrator burst

Check and replace relay

Electrical signals not working

- Blown fuse number 13

Replace fuse

- Relay P3 failed

Check and replace relay

The sound level of electrical signals has decreased

Adjustment broken

Remove signals and adjust

The signal makes a rattling sound

- A crack has appeared in the signal membrane

Remove the signal, disassemble and replace the membrane

Adjust signal

The noise relay-buzzer does not signal a decrease in air pressure in the brake system

- Fuse No. 8 blown

Replace fuse

- Buzzer relay failed

Replace relay

In the sound alarm system, it is necessary to monitor the purity of the sound signals; if dirty, they must be wiped with a dry rag.

The adjustment of electrical signals is carried out only if they fail after repair or when the volume is reduced.

Adjustment is made using the adjusting nuts. Loosen the nuts and turn them to achieve the best sounding signal, after which the nuts are tightened.

Possible malfunctions of the sound alarm system and how to eliminate them are shown in the table.

At the pneumatic signal, vibrators fail and must be replaced.

Repair of electrical signals usually comes down to replacing a failed membrane. The buzzer relay is not repairable, but must be replaced entirely.