SHAFT 6K9062 - Caterpillar

"Closed" Excitation Circuit (Field "on")
From bridge rectifier (CR9 and CR10) and capacitor (C1) current flows through wire (1) to PC board (M4), terminal #1 (8).From (M4), terminal #1, current flows through wire (1) to Regulator Terminal Strip, terminal (F1).From terminal (F1) current flows to exciter field (L2).From exciter field (L2) to Regulator Terminal Strip, terminal (F2).From terminal (F2) through wire (2) to PC board (M4), terminal #2 (7).From terminal #2 through a switching power transistor (3) on (M4) to terminal #3 (6) on (M4). On the self-excited generator the switching power transistor on (M4) is turned "on" during start-up by interconnecting circuitry on (M4 and M5) and by a plug-in relay - relay contact on (M5). During normal operation, a signal from the sensing and control board (M1) to PC board (M4) controls the switching transistor (3).
BUILD-UP RELAY RL501 (Self-Excited Generator)From terminal #3 through wire (3) to bridge rectifier (CR9 and CR10) and capacitor (C1)."Open" Excitation Circuit (Field "off")
The PC board (M4) also contains the intelligence part of a "Flyback" circuit which comes into play when the (M4) board switches open the excitation circuit. A flyback circuit from the negative (-) end to the positive (+) end of the exciter field (L2) permits a current flow when (M4) has switched open the excitation circuit.When the current flows through exciter field (L2) it causes a magnetic field around the coils of the field. The strength of the magnetic field is in relation to the current going through the exciter field. An increase in current flow makes the magnetic field stronger, and a decrease in current flow makes the magnetic field weaker.When the current through the exciter field (L2) stops because PC board (M4) has cut off the flow, the magnetic field strength is maximum. The field now starts to collapse (grow weaker) back into the conductors of the coil. As a result of this, a voltage is induced in the coil which is where the "flyback" circuit comes in.From the negative (-) end of the exciter field (L2) through wire (F2) to terminal (F2).From terminal (F2) through wire (2) to (M4), terminal #2.From PC board (M4), terminal #2 through a diode on board (M4) to terminal #1 on board (M4).From terminal #1 through wire (1) to Regulator Terminal Strip, terminal (F1).From terminal (F1) through wire (F1) to the positive (+) end of the exciter field (L2).The PC board (M4) also provides reference excitation current to the Overcurrent Protection Board (M2).On the self-excited generator, part of the voltage build-up circuitry is located on the PC board (M4). This circuitry allows the excitation circuit to remain in the "on" mode to allow voltage to increase from residual magnetism. As mentioned in this section and the section on PC board (M5), the main portion of the excitation voltage build-up circuitry is located on PC board (M5).Overcurrent Protection Board (M2)
The Overcurrent Protection Board (M2) is located second card from the left in the cage assembly (A5) - as viewed from the front of