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The "600" series Counters have been designed utilizing modular printed circuit boards and plug-in integrated
circuits. These design approaches, therefore, minimize maintenance and greatly facilitate troubleshooting. It will be
noted in the following sections that once critical check points have been located, the majority of the maintenance
problems can be solved merely by replacing defective components. It is anticipated, however, that maintenance will be
required much less frequently than ever before on this class of equipment.
Preventive maintenance is not required on a formal basis as occasional operating checks will determine if any circuitry is
functioning improperly.
4.1
The only calibration required on this instrument is the occasional monitoring of the internal crystal frequency. A
terminal on the rear panel is available for monitoring the 1 MHz crystal oscillator. This signal should be
compared with a suitable reference calibrated to WWV to insure the absolute accuracies within the capabilities of
this instrument.
4.2
Theory of Operation
The following paragraphs describe briefly the basic signal flow paths and the general operational characteristics
of the unit. Detailed circuit analysis is not undertaken since with the "600" series counter line the use of
integrated circuits obviates the necessity for such detail.
4.2.1
Integrated Circuits
Standardization of the circuitry used has made possible the minimization of IC types employed. The
basic IC circuits consist of NAND gates, NOR gates, Flip Flops and Decade Counters. Most IC's contain
multiple circuits and care must be exercised in troubleshooting to locate the proper pins on each IC. The
enclosed schematics and parts list show IC types and pin numbers to assist in circuit tracing. More detail
on the basic circuits within the IC's may be obtained from the IC manufacturer by requesting appropriate
data sheets if desired.
4-10
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