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Troubleshooting DC-To-DC Converter
Parallel NOR gates A4U1, A4U2 and A4U3A act as drive rs and switch on FETs A4Q1, Q2, Q3 and Q4 through pulse
transformer A4T1. NOR gate A4U3B turns off the FETs through pulse transformer A4T2 and transistors A4Q5 and A4Q6.
Circuits Included. On-Pulse Driver, Off-Pulse Driver, FET Switches and Drivers on A4 FET board.
Setup. The Main Troubleshooting Setup, page 33. Apply the ac mains voltage to the isolation transformer, and set the
external supply to 40Vdc. Set the unit's output voltage to 20Vdc and current to above 1Adc using "DISPLAY SETTINGS"
switch. Verify that the UNREGULATED LED lights. See Figure 3-3 for waveforms.
Inputs:
NODE ( + ) NODE ( - ) MEASUREMENT SOURCE
A2J7-26
(PWM-ON)
M1.7µs 20KHz pulse
(see Waveform 1)
A2J5-11, A2U15-1, A4P1-A3
A2J7-25
(PWM-OFF)
M10µs 20KHz pulse
(see Waveform 2)
A2U16-5, A2J5-13, A4P1-A2
A4P1-C1 M10.6Vdc A1U3-2
A4Q2-D A4Q4-S 39Vdc A1C5 (+), A4P1-22 to 25
A1C1(-), A4P1-16 to 18
Outputs:
NODE ( + ) NODE ( - ) MEASUREMENT
A4Q1/Q2-G A4Q2-S (see Waveform 3)
A4Q3/Q4-G A4Q4-S (see Waveform 3)
A4Q2-S A4Q4-D (see Waveform 4)
A2J7-18 A2J7-4 (see Waveform 5)
If you replace the FETs, replace both the FETs and associated drive components as furnished in FET Service Kit, Agilent
Part No. 5060-2866.
The FETs are static sensitive and can be destroyed by relatively low levels of electrostatic voltage.
Handle the A4 FET board and the FETs only after you, your work surface and your equipment are
properly grounded with appropriate resistive grounding straps. Avoid touching the FET's gate and
source pins.
Troubleshooting Down Programmer
The down programmer discharges the output when either PWM OFF is generated or CV ERRO R is more negative than
about - 3Vdc. Comparator A5U1 triggers down programming when the voltage at A5U1-5 is less than about 4Vdc.
Circuit Included. Down programmer and 10.6V bias supply on A1 main board.
Setup. The Main Troubleshooting Setup, page 33, except connect the external supply to the unit's + OUT ( + ) and – OUT
( - ) terminals. Apply the ac mains voltage to the isolation transformer. Set the external supply for an output voltage of
10Vdc and set current limit for 2.5 Amps. Set the power supply under test for a voltage setting of 8.0Vdc and current
setting of 2.0Adc using "DISPLAY SETTINGS" .