Agilent Technologies 856290216 Line Fuse Blowing, Supply Restarting Every 1.5 Seconds Kick Start

Line Fuse Blowing

1.If the line fuse blows with the (LINE) switch off, suspect either the input filter or the power switch cable assembly.

2.If the line fuse blows when the spectrum analyzer is turned on, disconnect the power

cord and lift the drain of A6Q102 from TP108. If the line fuse still blows, suspect CR102 through CR105.

3.If the fuse does not burn out immediately, check A6TP108 for a voltage of between +215 V and +350 V.

4.If the voltage at TP108 is correct, disconnect the power cord. Wait 60 seconds for the high voltage to discharge. Remove and check A6Q102.

5.If Q102 is shorted, Q103, Q104, CR108, U132 and U207 may also be shorted.

6.The “Buck Regulator” procedure in the “Dead Power Supply” section can be used to check the above components.

7.If Q102 is working properly, measure the resistance between TP102 and TPlOl (positive ohmmeter lead to TP102).

8.If the resistance is less than 1 kR, suspect either Q103 or Q104 in the DC-DC Converter.

Supply Restarting Every 1.5 Seconds (Kick Start)

See function blocks G, D, I, and L of A6 power supply schematic diagram in the component-level information binder. If there is a short on the power supply or on one of the other assemblies, the power supply will attempt to “kick start.” (Every 1.5 seconds the supply will attempt to start, but will be shut down by a fault condition.) The kick start and its bias circuits provide power for the control circuitry during power-up. The kick start circuitry is an RC oscillator which emits a 200 ms pulse every 1.5 seconds. These pulses switch current from the input rectifier through Q201 to charge C201. When the power supply is up, a winding on T103 provides power to the control circuitry. This voltage is high enough to keep Q201 turned

O f f .

1.Monitor the waveforms at TP206 and TP208 simultaneously on an oscilloscope.

2.If the signal at TP208 goes high before the signal at TP206 goes low, an overcurrent condition has been detected. Suspect a short in the secondary (output rectifier, voltage regulators, or another assembly).

3.Do the first three steps of the “Buck Regulator” procedure of the “Dead Power Supply” section to check the primary.

13-14 Display/Power Supply Section