The switch is checked using an oscilloscope and a rectangular pulse generator according to the diagram shown in Figure 141,a, with a supply voltage of 12 V. It is advisable to use a two-channel oscilloscope. One channel is used to monitor the generator pulses, and the second for the switch pulses.
Figure 141. Circuit for testing the switch (a) and the pulse shape on the oscilloscope screen (b): 1 - spark gap; 2 - ignition coil; 3 - switch; 4 resistor 0.01±1% Ohm, not less than 20 W, A - to the rectangular pulse generator; B - to the oscilloscope; t - current accumulation time; l - maximum current value; I - commutator pulses; II - generator pulses
When assembling a circuit to test the switch, make sure that the low-voltage wires are not in the same bundle with the high-voltage wires. In addition, it is not allowed to disconnect the plug from the switch with the ignition on (with the power supply voltage on), since in this case, voltage of up to 400 V may occur on individual elements of the switch circuit and the switch will be damaged.
Rectangular pulses with a frequency of 3.33 to 233 Hz from the generator, simulating sensor pulses, are fed to terminals "3" and "6" of the switch. The pulse duty cycle, i.e. the ratio of the period to the pulse duration, is Y/Yand=3. Maximum voltage Umax=10 V, and the minimum Umin≤0.4 V (figure 141.6). The output resistance of the generator should be 100-500 Ohms.
In a serviceable switch, the shape of the current pulses should correspond to the oscillogram I. The value of the current l should be 8-9 A, and the time t of its accumulation should be no more than 8.5 ms at a frequency of 33.3 Hz and no less than 4 ms at a pulse frequency of 150 Hz.
If the shape of the commutator pulses is distorted, then there may be interruptions in spark formation or it may occur with a delay. In this case, the engine will overheat and not develop rated power.
The article is taken from an online resource VAZBOOK.ru