644 Chapter12
Display/Power Supply Section
A6 Power Supply Assembly
Line Fuse Blowing
1. If the line fuse blows with the LINE switch in the off position, suspect
either the input filter or the power switch cable assembly.
2. If the line fuse blows when the HP 8560E/EC 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 is not burned out, 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, CR106, and CR108 are also probably
shorted. If Q102 is working properly, measure the resistance
between TP102 and TP101 (positive ohmmeter lead to TP102).
6. If the resistance is less than 1 kΩ, suspect either Q103 or Q104 in
the DC-DC Converter.
Supply Restarting Every 1.5 Seconds (Kick Start)
See function blocks G, H 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 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 off.
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).
Low Voltage Supplies
1. Connect the negative lead of a DVM to A6TP301.
2. Check A6TP302 for +15 Vdc.
3. Check A6TP303 for −15 Vdc.
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