Agilent Technologies 856290216 service manual Low Voltage Supplies, Buck Regulator Control Loop

Low Voltage Supplies

1.Connect the negative lead of the DVM to A6TP301 and verify the power supply voltages.

a.Check A6TP302 for +15 Vdc.

b.Check A6TP303 for -15 Vdc.

c.Check A6TP304 for +28 Vdc.

d.Check A6TP305 for -12.6 Vdc.

e.Check A6TP308 for i-5 Vdc.

f.Check A6TP307 for -5 Vdc.

2.If the voltages measured above are correct but the power supply LEDs on the A2 controller assembly are not lit, check Wl.

3.If the voltages are low, disconnect Wl from A6Jl and measure the test point voltages again. Unless a dummy load is connected to the A6 power supply, the voltages should return to their nominal voltages but be unregulated.

4.If the voltages do not return to near their nominal range, the A6 power supply is probably at fault.

Buck Regulator Control Loop

Part of the buck regulator control circuitry is on the A6 power supply assembly and part of it is on the A6A2 regulator board, that is part of the A6 power supply assembly. The control circuitry can be checked as follows:

1.The voltage at E302 should be 6.8 V.

2.If not, check for a triangle wave on the regulator board at TP31, or a 35 V peak-to-peak square wave at CR305 pin 3.

3.If these signals are not present, check the VBUCK signal for a voltage of about 110 V, and check Q103 and Q104 for proper switching.

4.If the 6.8 V control loop is functioning properly TP33, on the regulator board, should be about 0 V.

5.The feedback signal is pulse width modulated to drive the opto-isolator U206. Check for a rectangular waveform at U206 pin 3, to verify its operation.

High Voltage Supplies

1.Set the m switch off, disconnect the power cord, and remove the power supply shield.

2.Connect the negative lead of the DVM to A6TP401 and positive lead to A6TP405.

3.Set the (LINE) switch on.

4.If the voltage displayed on the DVM is approximately i-110 Vdc and the rear-panel CRT i-110 VDC ON indicator is lit, A6Al HV module is probably at fault.

Display/Power Supply Section 13-15