HP 428B, Operating And Service Manual, Page: 36 / 52

Model 428B
SECTION VII
CIRCUIT DIAGRAMS
7-1. INTRODUCTION.
7-5. SCHEMATIC DIAGRAMS.
7-2. This section contains the circuit diagrams necessary
7-6. The circuitry contained within each assembly is
for the operation and maintenance of the Model 428B
shown in the schematic diagrams. These diagrams are
Clip-on DC Milliammeter. Included are a block diagram,
used to develop an understanding of the detailed theory
schematics and component location diagrams.
of operation of each assembly and as an aid in isolating
troubles within an assembly.
7-3. BLOCK DIAGRAM.
7-4. The block diagram shows the relationship between
7-7. COMPONENT LOCATION DIAGRAMS.
the assemblies of the instrument. Signal flow between
7-8. The component location diagrams show the
assemblies and significant portions of assemblies as well
physical location of parts mounted on an assembly.
as major feedback paths are shown. The block diagram Each part is identified by a reference designator.
is used to develop an understanding of the basic theory
of operation.
SCHEMATIC NOTES
MEASUREMENT CONDITIONS.
Line voltage: 115 V, 60 Hz
Range:
100 mA
Input: 100 mA
All voltages were measured with a high input impedance
electronic voltmeter. A 10 megohm oscilloscope probe was
used to measure the waveforms. The oscilloscope should be
externally synchronized from pin 2 of V7 (through a 47 µF
capacitor to avoid disturbing the circuit.
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