34
Table 3 5. Performance Failure Symptoms (continued)
SYMPTOMS DEFECTIVE
BOARD
CHECK FUNCTIONAL CIRCUITS
CV overshoots A2 A2U10A, A2CR20, A2R94
Output noise ( < 1KHz) A2, A1 CV Circuit
Output noise ( > 1KHz) A1, A4 Transformer A1T1, Output Filter, snubbers A4R7
/R8 /C5 / CR5, A4R13/ 14 / C6 /CR6, A4R33 /C13
CV regulation, transient response,
programming time
A2, A1 Wrong sensing (paragraph 3-40), low ac mains
voltage, CV Circuit
CC regulation A2 Low ac mains voltage, CC circuit
CV oscillates with capacitive loads A2 A2U10, A2C51, A2R95, A2R96, A2R86, A2C47,
A2R71, A2C36
CC oscillates with inductive loads A2 A2U10, A2R86, A2C47, A2C43, A2R77, A2U3D,
A2R30, A2C44, A2R76, A2R75, A2C42, A2C41,
A2R16
+15V on A2 Control Board. Voltage regulator A2U12 regulates the voltage across resistor A2R29 to be 1.25Vdc. That
sets the current through zener diode A2VR1 at 7.5mAdc. The output voltage is 1.25Vdc plus 11.7Vdc across A2VR1 plus
the voltage across A2R34.
Circuit Included. + 15Vdc bias supply circuitry from connector pin A2P1-27 through test point A2J3-2 on A2 control
board.
Setup. The Main Troubleshooting Setup, page 29. Apply the ac mains voltage to the bias transformer, and set the external
supply to 0Vdc.
Input:
NODE (+ ) MEASUREMENT SOURCE
A2U12(IN), A2C17(+) ≈ 24Vdc A1U1, AlC1 (+)
Outputs:
NODE ( + ) N0DE ( - ) MEASUREMENT
A2U12 (OUT) A2U12 (ADJ) 1.25Vdc
A2U12 (cath.)
A2U12 (anode.) 11.7Vdc
A2VR1 (anode.)
A2R34, A2R33 2.05Vdc
A2LR3 (cath.)
A2VR3 (anode.) 6.2Vdc
To check if load on + 15V is shorted, remove jumper A2W1 .
-15V on A2 Control Board. Voltage regulator A2U4 regulates the voltage across resistor A2R32 to be 1.25Vdc.
Circuit Included. -15Vdc bias supply circuitry from co nnector pin A2P1-30 through test point A2J 3-21 on A2 control
board.
Setup. The Main Troubleshooting Setup, page 29. Apply the ac mains voltage to the bias transformer, and set the external
supply to 0Vdc.