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, 15∝s pulses, 45KHz

 

A2Q3 (emit)

≈ 20Vpk, 5∝s 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

Potentiometers.

A3R4, A3R5

or always max

 

 

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

CHECK FUNCTIONAL CIRCUITS

 

BOARD

 

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

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Agilent Technologies AGILENT MODELS 6023A and 6028A service manual Troubleshooting Bias Supplies, Node + Measurement Source