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Model 547A
Page 7
DC AMPLIFIER AND DISPLAY DRIVER.
The signal at C15 is de-coupled to this amplifier, which consists of an
operational-amplifier (p/o U3) and series-pass transistor Q3. The gain is set by R25 and R27; C19 is provided to
suppress oscillations.
MAINTENANCE
PROBE DISASSEMBLY.
To disassemble Current Tracer, refer to Figure 6, and proceed as follows:
1.
With fingers, unscrew (ccw) the plastic indicator light window (MP4).
2.
Slide the bottom shell off probe tip end (MP1).
3.
Lift the top shell off the probe (MP2).
4.
Carefully separate the circuit board and cable assembly.
PROBE ASSEMBLY.
Reverse disassembly procedure.
ITAUTION
BE CAREFUL WHEN REPLACING PARTS ON THE FRAGILE PRINTED-CIRCUIT
BOARD. EXCESS HEAT CAN RUIN THE BOARD. USE A LOW WATTAGE SOLDER-
ING IRON
(~25
WATTS) AND APPLY THE MINIMUM HEAT NECESSARY TO
UNSOLDER THE LEADS.
PREVENTIVE MAINTENANCE.
No periodic adjustment or preventive maintenance procedures are necessary for
the Current Tracer.
ADJUSTMENTS.
Potentiometer R21 is the only maintenance adjustment in the Model 547A. This trimmer may be
used as a supplementary adjustment to the gain control (R3) and as a troubleshooting adjustment. Refer to infor-
mation adjacent to the schematic diagram. Preliminary adjustment of R21 is made by setting the wiper arm ap-
proximately midway in its range. If this setting results in too little or too much sensitivity, with R3 set at the 1 rnA
end, then R21 can be adjusted to correct this. To assure there is 1 rnA in the test circuit- refer to Figure 7.
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