33
Troubleshooting Bias Supplies
+5V on A2 Control Board. The PWM A2U6 includes a clock generator (45KHz set by A2R53 and A2C26), and a current
limit (2Adc set by 0.15Vdc across A2R50). It turns off each output pulse using the difference between the voltage at
voltage divider A2R46-A2R47 and the 2.5Vdc set by voltage regulator A2U5.
Circuit Included. + 5Vdc bias supply circuitry from connector pin A2P1-15 through jumper A2W3 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
A2J3-22
≈ 20Vdc
A1CR6,A1CR7
Outputs
NODE MEASUREMENT
A2U6-6
≈ 2 to 4Vdc sawtooth, 45KHz
A2U6-12,13
≈ 19Vpk, 15µs pulses, 45KHz
A2Q3 (emit)
≈ 20Vpk, 5µs pulses, 45KHz
A2U5 (OUT) 2.5 Vdc
A2R50, A2CR11 (anode)
≈ 0 > V > -0.07Vdc
A2R161, A2R163 2.5 Vdc
To check if load on + 5 V is shorted, remove jumper A2W3
Table 3-4. A3 Front-Panel Board Failure Symptoms
SYMPTOMS DEFECTIVE CIRCUIT CHECK COMPONENTS
Error when pressing DISPLAY SETTINGS Limits display. A3U1, A3U9
Error in VOLTS or AMPS Input ranging or DVMS. A3U1,A3U2,A3U4,A3U5,A3U7
* one or more display digits out Display LEDs. A3DS1 through A3DS7
Unable to adjust VOLTAGE or CURRENT
or always max
Potentiometers. A3R4, A3R5
VOLTS decimal point error Decimal drivers. A3U6
* Note that the Volts and Amps tests (Table 3-3 pins 5 and 6) verify that all the current and voltage display segments light
except for the decimal points.
Table 3 5. Performance Failure Symptoms
SYMPTOMS DEFECTIVE
BOARD
CHECK FUNCTIONAL CIRCUITS
Unexplained OVP shutdowns A2 OVP Circuit, CV Circuit
No current limit A2 CC Circuit
Max current < 30Adc A2 CC Clamp, CC Circuit
Max power < specified A2, A1 Power Limit, 20KHz clock, transformer A1T1
Max voltage < 20Vdc A2, A1 CV Circuit, diodes A1CR1-CR4
Cycles on & off randomly A2, A1 AC-Surge-&-Dropout Detector, Mains Voltage
Select switch A1S2
