175A - HP Archive

Section V
Paragraphs 5-93 to 5-100
m,
Procedure Effect
Connect DC Voltmeter to pin 2 of V204.
Adjust HORIZONTAL POSITION for
reading of 0 volt.
Measure voltages at pin 1 of V204 and
pin 1 of V205.
de 5-8 Horizonta
Measure voltages at pins 3 and 8 of V208.
5- 93. HORIZONTAL AMPLIFIER.
5-94. Signal waveforms and their associated dc levels
are given as a troubleshooting aid on the horizontalamplifier
schematic diagram, figure 5-28.
5-95. If the horizontal amplifier appears to operate
properly with the HORIZONTAL DISPLAY in any of
the external input positions, but not in internal sweep
positions, the trouble is most likely in the sweep
generator.
5-96. If the horizontal amplifier appears to operate
properly with the HORIZONTAL DISPLAY in the
internal sweep positions, but not in any of the external
input positions, the trouble is most likely associated
with the horizontal input amplifier.
5-97. UNBALANCE. The cause of unbalance in the
horizontal amplifier will most likely be associated
with V204, V205, V208, or V209 since these are the
only stages connected in the differential configuration.
Measurement of dc voltages on each side of the
amplifier is the best method to use to isolate the
cause of unbalance because of the feedbackused in the
amplifier. Proceed as in table 5-8.
5-98. GAIN. If the amplifier has the wrong gain
ensure that it cannot be corrected by adjusting Gain
Adj R213, X1 Gain Adj R225, or X10 Gain Adj R227.
The waveforms given on the schematic diagram, figure
5-28, provide information on the gain of each
stage. Start at the input and proceed toward the
deflection plates.
5-99. CATHODE RAY TUBE REPLACEMENT.
5-100. To replace the crt in the Model 175A,proceed
as follows:
WARNING
To prevent injury to eyes and hands if crt
breaks, wear plastic face mask or goggles
and insulated gloves. Handle the crt with
extreme care.
5-18
Amplifier Troubleshooting
0 volt reading impossible
Correct reading
Voltages unequal
Voltages approx equal
Voltages unequal
Voltages approx equal
Trouble
R262 or V203
Input circuitry good
V204 or V205
V204 and V205 good
V208 or V209
V208 and V209 good
a. Remove top cover of instrument.
Model 175A
b. Remove all leads connected to neck of crt (see
figure 5-12).
c. Remove post accelerator cap from crt (located
near front of crt case).
d. Carefully remove bakelite plug from base of crt.
e. Remove screws from clamp at base of crt and
remove top half of clamp. If necessary loosen bottom
half of clamp.
f. Remove front panel crt bezel.
g. Carefully slide crt out through frcnt panel hole.
Light mask removes with crt.
h. Installation of replacement crt is essentially
the reverse of removal procedure described above.
Refer to figure 5-2 for correct connection of deflec-
tion leads. Do not over-tighten base clamp or tube
may be damaged. Before tightening clamp, rotate
crt until bottom of graticule is parallel with bottom
of front panel and be sure light mask just touches
bezel.
i. Obtain a free running trace and adjust TRACE
ALIGNMENT until trace is aligned with horizontal
lines of graticule.
j. Make checks and adjustments, if necessary,
referred t.0 in the following paragraphs in the order
given: 5-37 through 5-39, 5-42 through 5-46, 5-51,
5-52, and 5-55 through 5-57.
01526-2