Model 175A Section V
Paragraphs 5-61 to 5-73
5-61. EQUIPMENT REQUIRED. Model 1780A:
SWEEP OCCURRENCE ... NORMAL
Model 1781A/B: 5-62. In general, miniaturized equipment calls for
miniature tools. The following are particularly
SWEEP SELECTOR. . MAIN SWEEP important:
Model 1782A:
a. Low-heat soldering iron (25 to 50 watts). Idling FUNCTION. ........... OFF
temperature must be no more than 800°F. Model 1783A:
MARKER ............ OFF
b. Small soldering iron tip (1/16 to 3/32 inch).
c. Depress BEAM FINDER.
c. Small-diameter rosin-core solder.
d. A defocused spot should appear on the crt.
d. Wooden toothpick.
e. If proper display is obtained, it is likely that
the power supplies are operating properly. If no spot
5-63. The low-heat iron is required in order to pro-
tect solid-state devices from too high a temperature, appears, troubleshoot the power supplies (paragraphs
and to avoid causing conductors to lift from the printed 5-70 and 5-77) and the amplifiers (paragraphs 5-81
and 5-93).
circuit boards. The small tip will transfer less heat
to the component, yet will be adequate to melt the f. Connect CALIBRATOR 10 VOLT output to ver-
solder. Small-diameter solder melts more quickly, tical INPUT and HORIZ INPUT,
reducing the length of time that heat mustbe applied.
The toothpick is essential for cleaning out mounting
holes after removing a component. Do not attempt g. A tilted straight line pattern with a 10-cm hori-
zontal deflection and 5-cm vertical deflection should
repairs on the Model 175Aunless the above equipment be obtained.
is on hand.
h. If proper display is obtained, it is likely that
5-64. PROCEDURE. the horizontal amplifier, vertical amplifier, and cali-
brator are operating properly.
5-65. The Model 175A has plated-through circuit
boards. Each component mounting hole is plated i. Set:
through in order to provide electrical conduction from
HORIZONTAL DISPLAY. ......... X1
one side of the board to the other and to provide a SWEEP MODE ........... PRESET
better solder bond between the circuit and the com- SWEEP TIME .......... 1 MSEC/CM
ponent. The plating is easily damaged by reaming
the hole with a metal tool, or by forcing component Sweep VERNIER ............ CAL
leads into the hole. The use of the wooden toothpick TRIGGER LEVEL ............. 0
for cleaning out solder, and ordinary care in replacing TRIGGER SOURCE ........... INT
the component, will result in a satisfactory job. j. A synchronized square wave pattern 5 cm high
should be obtained.
5-66. REPLACINGTRANSISTORS. Solid-state diodes
and transistors require special handling, in that they k. If proper display is obtained, it is likely that
the sweep generator is operating properly.
are sensitive to both heat and electrical overload.
Use long-nose pliers between the iron and the device
as a heat sink. Hold the pliers for a moment after 5-70. LOW-VOLTAGE POWER SUPPLIES. -
the iron is removed to allow the joint to cool. Be sure
there is no electrical leakage from iron to work. Such 5-71. The transistors used in the power supply are
leakage can damage transistors. located on the power-supply printed-circuit board and
fan-shroud assembly. The series-regulator tran-
sistors are power transistors mounted on heat sinks
5-67. TROUBLESHOOTING. on the fan-shroud assembly. The amplifier and other
transistors are mounted on the printed circuit board
5-68. ISOLATING TROUBLES TO A MAJOR (figure 5-33).
SECTION.
5-69. The following check may be performed when- 5-72. If maintenance on the fan-shroud assembly is
ever instrument malfunction is suspected. required, it may easily be removed from the instru-
ment by removing the mounting screws on rear gusset.
However, power supply malfunctions can generally
a. Set: quickly be isolated to components either on the printed
HORIZONTAL DISPLAY , . 1 VOLT/CM AC circuit board or on the fan-shroud assembly, thus
EXTERNAL VERNIER .......... CAL eliminating unnecessary removal of the fan-shroud
Vertical SENSITIVITY ... 2 VOLTS/CM ass e mbly .
Vertical Sensitivity VERNIER. ..... CAL
5-73. Nominal voltages at key points in the supply
b. Depending on the model number of the horizontal are given on the Low-Voltage Power-Supply schematic
plug-in unit, set controls as follows: diagram, figure 5-34.
01526- 1 5-13 |
ACEC
