HP 8559A Operation And Service Manual page 330

MODEL 8559A
If the residual FM is unchanged, assume that the YTO Main Coil Fixed Driver is not its source. Retune the
HP 8559A to minimum, .010 GHz. Isolate the YTO Main Coil Filter from the circuit by mounting the
Frequency Control Assembly A7 on an extender board and taping over PI-19, PI-20, P1-25, while short-
ing PI-2 to PI-19.
If the residual FM is unchanged, the probable source is the YIG-Tuned Oscillator Assembly A6.
If isolating the YTO Main Coil Tune Driver from the frequency control circuit eliminates the residual FM,
proceed to further isolate the source by shorting the sweep from block A to ground. This is best accom-
plished by shorting the input side of R80 to the ground side of R63. Use a short jumper to prevent the
induction of line frequency noise into the circuit.
If the residual FM is eliminated, the source is probably the FM/Main Coil Sweep Switch. The most
common failure is U15.
If residual FM is present after shorting the input sweep, remove the jumper and substitute a battery for the
tune voltage. Do this by carefully unsoldering the input side of R82 and inserting a battery (5V to 10V)
between the free end of R82 (the
shortest possible leads to prevent line frequency noise pickup.
If residual FM is unchanged, the probable source is the YTO Main Coil Tune Driver. The most common
failures are: U10, R72, R76, R61, R80, R63, and R62, in that order.
In this step, the
-
negative battery lead to pin 3 of U12; attach the positive
(- )
residual FM is eliminated, the probable source is the Tune/Full Span Voltage (block B). If the residual FM
is unchanged, remove the battery and the tape. Tune the FINE TUNE control to minimum, remover the
(945) wire from the COARSE TUNE control (A2R1), and attach the battery's negative
COARSE TUNE control in place of the (945) wire. Attach the positive
of R63. This test is necessary to eliminate the TUNING control as a source of residual FM.
If using the battery in place of the
probable source. All of the regulator parts can cause instability; however, the most common failures are:
U7, R30, R33, R32, C3, R29, and VR2 (block H), in that order. Also, verify that all supplies are properly
adjusted.
If the Tune/Full Span Voltage (block B) is the probable source of the FM, the most common failures are
U12 and 413.
If isolating the YTO FM Coil Driver eliminates the residual FM, short the incoming sweep to ground.
Install a jumper between the input side of R97 and the ground side of R95. Use the shortest possible lead
to minimize line frequency noise pickup.
If the residual FM is unchanged, the source is probably the YTO FM Coil Driver. The most common
failures are U13 and U14.
If the residual FM is eliminated, the source is probably the FM/Main Coil Sweep Switch. The most
common failure is U15. If the residual FM is unchanged, short TP8 to ground. If this eliminates the
residual FM, the source is probably on the Marker Assembly A8.
If isolating the YTO Main Coil Fixed Driver eliminates the residual FM, it is probably the source of the
FM. The most common failures are: U2, C1, R1, and R2, in that order.
If removing the YTO Main Coil Filter from the circuit eliminates residual FM, it is probably the source of
the FM. The most common failure is Q5. If the FM is not eliminated, the most common failures are
terminal) and the grounded end of R63 (the
-
-
+
terminal). Use the
lead to the grounded end of R63. If the
(+)
battery lead to the ground side
(+ )
-
SERVICE
(- ) lead to the