CONTROL GP-WINCH 1258247 - Caterpillar

Before starting the engine see the topic INITIAL OPERATING PROCEDURE AFTER REPAIR.
Testing Surge Suppressor
Mark and disconnect the surge suppressor leads from terminals F+ and F- on the heat sink terminal board. Touch the surge suppressor leads together to discharge the capacitor in the suppressor. Set the ohmmeter to read on the highest scale. Connect one ohmmeter lead to a surge compressor lead. Watch the ohmmeter when connecting the other ohmmeter lead to the suppressor lead. The ohmmeter needle should move toward zero and then return toward infinity.Testing Power Rectifiers And Controlled Rectifiers
See Fig. 17. The power rectifiers and controlled rectifiers used in the SRCR generator are of the silicon diode type. Particular care must be exercised in the original installation, testing and replacement of the power rectifiers.
FIG. 17. RECTIFIERS
1. Controlled rectifier. 2. Power rectifiers.Power rectifiers are subject to failure due to: 1. Excess current.2. Excess voltage.3. Excess heat.4. Excessive tightening.If a diode rectifier or a controlled rectifier should fail, it will normally fail shorted, but it may fail open.Testing Power Rectifiers
See Fig. 18. An ohmmeter check will not give an accurate indication as to the quality of the rectifier. Such a test will indicate only if the rectifier is open or shorted. Since most rectifiers that fail will fail shorted, an ohmmeter check is the most logical starting point in troubleshooting the power rectifiers.
FIG. 18. TESTING POWER RECTIFIERA typical good rectifier will show approximately 10 ohms resistance in the forward direction and 30,000 ohms or more in the reverse direction, as measured with a commercial ohmmeter. Commercial ohmmeters utilize a dry cell battery (usually 1 1/2 volts) to cause a current flow to permit a direct reading resistance measurement. Due to low reverse voltage and low forward current, the ohmmeter can not give an indication as to the quality of either a power rectifier or a controlled rectifier. The error in measuring reverse resistance of a rectifier may be as much as 100 to 1.Testing Controlled Rectifiers
An ohmmeter check will not give an accurate indication as to the quality of the controlled rectifier. Such a test will indicate only if the controlled rectifier is either shorted or open. Place the positive lead of an ohmmeter on the stud and the negative ohmmeter lead on the pigtail. Take this reading and reverse the ohmmeter leads and compare the two readings. A shorted controlled rectifier will indicate zero or equally low resistance for both readings; an open will show infinite readings. If the controlled rectifier is neither shorted nor open, it will show approximately equal readings above 30,000 ohms. To test the gate circuit for either shorts or opens, alternate the positive and negative leads of the ohmmeter to the pigtail and gate lead. If the gate circuit is shorted, both readings will be zero; both readings will be infinite resistance if the gate circuit is open. If the gate circuit is neither shorted nor open, both readings will be nearly equal and be approximately 10 to 100 ohms.Power Rectifier