1. Start the engine and let it run for at least 15 minutes. Remove the protective cover from the terminal "30" generator and by setting the engine speed 3000–3500 min–1, measure the voltage at the output "30". To do this, connect one lead of the voltmeter to the lead "30" generator, and the other - to the generator housing. In this case, the voltmeter should show a voltage of 13.6–14.6 V.
Checking the generator rectifier unit
You will need a pilot lamp (12V, 3W).
Attention! A burning lamp when checking negative diodes may also indicate a short circuit in the stator winding to the generator case, however, such a malfunction is much less common than short circuit diodes.
2. Check the rectifier diodes with a 12V test light and battery (see explanation). To test for shorts in the positive and negative diodes, connect "+" batteries through the control lamp to the output "30" generator, and "–" batteries - to the generator housing. If the lamp lights up, then there is a short circuit in the diodes and the unit must be replaced.
Explanation. You can check the rectifier unit without removing the generator from the car. To do this, disconnect the wires from the battery and the generator, and also remove the block with the wire from the output of the voltage regulator. For clarity, the test is shown on a generator removed from the car.
3. To test positive diodes, connect "+" battery through the control lamp to the output "30" generator, and "–" battery - to one of the bolts securing the rectifier unit. If the lamp is on, then there is a short circuit in the positive diodes and the unit must be replaced.
4. To test negative diodes, connect "+" battery through a test lamp to one of the rectifier unit mounting bolts, and "–" battery - to the generator housing. If the lamp lights up, then there is a short circuit in the negative diodes. block needs to be replaced (see warning).
5. To test additional diodes, connect "+" battery through the control lamp to the output "61" generator, and "–" battery - to one of the bolts securing the rectifier unit. If the lamp lights up, then there is a short circuit in the additional diodes. The rectifier block must be replaced.