Service manual

Inputs:

NODE (+) NODE (-) MEASUREMENT SOURCE

A2J3-26(PWM-ON) VM waveform #1 A2Ul7-6,A2P1-7, A4P1-24,C

A2J3-25(PWM-OFF) VM waveform #2 A2U13-5,A2P1-13,A4P1-26,A

A4Q3-D A4Q4-S 39Vdc A1C4 ( + ),A4P1-10,A,C

A1C4 ( - ),A4P1-4,A,C

Outputs:

NODE (+) NODE (-) MEASUREMENT

A4Q3-G A4Q3-S waveform #3

A4Q4-G A4Q4-S waveform #3

A4Q3-D A4Q3-S waveform #4

A4Q4-D A4Q4-S waveform #4

A2J3-18 A2J3-4 waveform #5

Note: The Gate (G) and Source (S) leads of PFETs A4Q3 and A4Q4 can be accessed from the circuit side of the

board and used as test points. The Drain (D) of A4Q3 can be picked up at its case or from the cathode of

A4CR13. The Drain of A4Q4 can be picked up at its case or from the anode of A4CR14.

If all the INPUT measurements are correct but the OUTPUT Vgs waveform (3) is incorrect, the problem may be caused by

weak PFETs. Two 6800pF capacitors (P\N 0160-0159) can be substituted for the PFETs (G to S) to check waveform 3. If

the waveform is still incorrect, the problem may be located in the drive components. If you replace the PFETs, replace both

the PFETs and associated drive components as furnished in PFET Service Kit. Agilent Part No. 5060-2860.

The PFETs are static sensitive and can be destroyed by relatively low levels of electrostatic voltage.

Handle the A4 power mesh board and the PFETs only after you, your work surface and your equipment

are properly grounded with appropriate resistive grounding straps. Avoid touching the PFET's gate and

source pins.

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 pins A2P1-15 through jumper A2W3 on A2 control board.

Setup. The Main Troubleshooting Setup, Page 48. 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