PISTON AS 6E6151 - Caterpillar

SR4 Generator Sets For 3200, 3300, 3400, 3500 Series EnginesReference: Service Magazine, August 22, 1983, "Improved Voltage Regulator Assembly Now Used". This article lists several improvements made to the voltage regulator assembly, including a solid state-type surge suppression diode (4W5272 or 4W5273 Suppressors). Suppressors (surge suppression diodes) are used to prevent high voltage surges from damaging other voltage regulator components. If high voltage surges are a problem, and occur over a period of time, failure of the suppressor can occur. The new solid state suppressors are as reliable as the former selenium-type suppressors, but are more difficult to troubleshoot if a failure occurs.
A failure of the former selenium-type suppressor would produce a distinctive odor and/or burn spots on the suppressor. The new solid state suppressors do not show any easily detectable signs of failure. In some cases, the ohmmeter test described in the Service Manual may not identify a defective suppressor (CR11 Suppressor Diode). If the generator set voltage starts to rise but quickly returns to zero, or if the voltage regulator repeatedly blows fuses, use the following procedure to troubleshoot the CR11 Suppressor Diode.
Procedure To Detect A Failure Of The CR11 Suppressor Diode.
1. Shut the engine down and be sure there is no voltage on the generator.2. Check the temperature of the suppressor. If it is hot to the touch it is probably defective. Use the illustrations and Step 3 to check the suppressor.3. To test the suppressor it is necessary to apply AC voltage to the suppressor circuit. Illustration 1 shows the test using 120 Volt AC current to activate the suppressor. Illustration 2 shows the test using 240 Volt AC current to activate the suppressor. The chart shows the appropriate voltage to use for each suppressor and voltage regulator.
Illustration 1. Test using 120 Volt AC current.
Illustration 2. Test using 240 Volt AC current.When the light bulb(s) are connected and voltage is applied, the bulbs should not light. If the bulb(s) light, even dimly, the CR11 Suppressor Diode being tested is defective and should be replaced.