HP 8559A Operation And Service Manual page 386

SERVICE
Second Xtal Pole (G)
The operation of the Second Xtal Pole is identical with the First Xtal Pole.
Second LC Pole (F)
Operation of the Second LC Pole is the same
as PIN diode CR5.
Output Buffer Amplifier (H)
The Output Buffer Amplifier is
its output current boosted by Q10. The current through input FET Q9 is established by R53:
Which becomes:
The total current through Q9 and Q10 is set by R54. The input signal path is selected by either CR15 (during
crystal mode) or CR16 (during LC mode).
BANDWIDTH FILTERS No. 1 and No. 2 ASSEMBLIES A1
Observe front panel switch positions in relation to the problem to isolate the area of the failure.
Check for leaky diodes and capacitors. Loading of the signal path can alter either a pole's gain or bandpass
shape or both.
Isolate crystal poles from LC poles to prevent interaction of failure symptoms. Isolation of the crystal poles
from the circuit is best achieved by removing CR8 and CRl5 (blocks D and G). Isolation of the LC poles is best
achieved by removing CR9 and CR16 (blocks C and F).
as the First LC Pole, except that R56* performs the same function
a
complementary pair of transistors in which Q9 acts
I,,,
=
I,,,
as a source follower with
and A1 3, TROUBLESHOOTING
MODEL 8559A