17
Chapter 6
Theory of Operations
General
The Valhalla Scientific Model 4021 Digital Ohmmeter is shown in block diagram form in Figure 2.
All information disclosed in this section is proprietary and is included in order to make
troubleshooting to component level possible.
The Model 4021 uses solid-state semiconductors exclusively and CMOS circuits extensively to
minimize power requirements and make battery operation practical.
Figure 2 Model 4021 Block Diagram
Troubleshooting
Malfunctions are often the result of misinterpretation of specifications or due to an incomplete
understanding of the instrument.
A thorough review of the operating instructions for this
instrument is recommended prior to any component replacement.
Check to be sure that cables
and other test equipment are in good working order before attempting to troubleshoot the 4021.
If the Model 4021 exhibits problems that cannot be eliminated by reviewing Chapter 3 and 5, the
following guidelines have been established to help solve the problem.
Current
Source
Range
Switch
Load
Amp.
A/D
Converter
Led
Display
DC
Reference
Display
Driver
120 kHz
Oscillator
