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Power Supply Section
Figure 4-8 shows the power supply section block diagram.
The ac line power is connected to the A5 AC Inlet Board Assembly, which consists of the fuse,
line switch, and varistors. The voltage selection switch on the rear panel selects the ac line
voltage from 230V or 115V. According to the selection, the ac line power is connected to the
corresponding primary tap of the transformer. Varistor, VR1 protects the circuit from surge
voltage on the line power. VR2 blows fuse F1 if the 4338B is turned on with the wrong line
voltage setting selection, for example, 115V selection when using a 230V line.
The transformer secondary voltage is approximately 14 V. The ac voltage is recti ed and
ltered by circuitry on the A1 Main Board Assembly, and produces approximately 14V dc. The
dc voltage is applied to the DC-DC Converter to produce regulated +12V, +5V, and 12V dc.
The dc voltages are supplied to all assemblies, either directly or indirectly via the A1 assembly.
4-10
T roubleshooting
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