VALVE-MULTI CIRCUIT PROTECTION 7U5835 - Caterpillar

Negative Diode Check
Illustration 1 g00869032
(1) stator (2) stator leads
Disconnect all stator leads (2) from the rectifier.
Disconnect the lead for the capacitor from the "D+" terminal.
Set the multimeter to the diode scale.
Illustration 2 g00868986
(3) Frame (4) Rectifier terminals
Connect one of the multimeter leads to one of the rectifier terminals (4). Connect the other multimeter lead to the frame (ground).
Record the multimeter reading.
Reverse the multimeter leads.
Record the multimeter reading.Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.Results:OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 4 through 7 for the other rectifier terminals (4). STOP.NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.Positive Diode Check
Illustration 3 g00868988
Positive diode check (inside view) (4) rectifier terminals (5) Connection to the "B+" terminal
Illustration 4 g00868990
Positive diode check (outer view) (4) Connection to the rectifier terminals (5) "B+" terminal
Stator leads (2) remain disconnected from the rectifier.
The multimeter remains on the diode scale.
Connect the multimeter leads across one of the rectifier terminal (4) and "B+" terminal (5) .
Record the multimeter reading.
Reverse the multimeter leads.
Record the multimeter reading.Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.Results:OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 3 through 6 for the other rectifier terminals (4). STOP.NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.Exciter Diode Check
Illustration 5 g00868991
Test for the Excitation diodes (inner view) (4) Rectifier terminals (5) (To the D+ terminal)
Illustration 6 g00868994
Test for the excitation diodes (outer view) (4) Rectifier terminals (5) (To the D+ terminal)
Stator leads (2) remain disconnected from the rectifier.
The multimeter remains on the diode scale.
Connect the multimeter leads across one of the rectifier terminal (4) and "D+" terminal (6) .
Record the multimeter reading.
Reverse the multimeter leads.
Record the multimeter reading.Expected Result: One reading is "0L" and the other reading is .4 to .9 volts.Results:OK - One reading is "0L" and the other reading is .4 to .9 volts. The diode is normal. Repeat steps 3 through 6 for the other rectifier terminals (4). STOP.NOT OK - Both readings are "00". The diode is shorted. Replace the rectifier. STOP.NOT OK - Both readings are "0L". The diode is open. Replace the rectifier. STOP.Note: The 35 amp alternator has three exciter diodes and three stator leads. The remaining alternators have three exciter diodes and four stator leads. If the alternator has four stator leads, do not test the stator lead with the black mark. The stator with the black mark lacks an exciter diode. Ignore the result for that stator lead. See Systems Operation, "Component Description" for more information on the stator and on the stator leads.