HP 3478A Technical Manual page 74

3478A
nal Trigger, etc.). Go to Service Group D, paragraph 7-
D-5, if any of the failures are detected. The following
explains the failures.
a. Turn-On Failure. A Turn-On Failure is when the
3478A's Keyboard Display, and HP-IB is dead (i.e., the
3478A is completely inoperative).
caused by the Main Controller (U501) and associated
circuitry.
b. Inoperative Display. An Inoperative Display is
when part or all of the 3478A's display is inoperative.
This can be caused by the display itself or the Main
Controller Circuitry.
c. Inoperative Keyboard.
Keyboard is when part or all of the 3478A's keyboard is
inoperative. This can be caused by the keyboard itself or
the Main Controller Circuitry.
d. Control ROM Failure. A failure caused by the
Control ROM normally shows up as a "U.C, ROM FAIL"
(after the 3478A's Self-Test). The ROM (U502) itself can
be the cause in addition to the Main Controller (U501)
and latch U513. A defective ROM can also show up as a
Turn-On Failure.
e. U.C. RAM Fails. This failure shows up as a
"U.C. RAM FAIL" after the 3478A's Self-Test routine. It
shows that the Main Controller's internal RAM has failed
its self-test.
f. Calibration RAM (CMOS RAM) Failure. This
failure can show up as a "CAL RAM Fail" after the
3478A's Self-Test routine. The RAM (U512) itself can be
the cause or the Main Controller Circuitry.
g. HP-IB (Remote) Failure. This failure is most
likely caused by the HP-IB Chip (U503), but can also be
caused by other circuitry in the Chassis Common Logic
Circuitry.
This is most likely
An Inoperative
7-4
7-34. Floating Common Logic Failures (Service
Group D). Floating Common Logic Failures are
normally caused by the A/D Converter or the A/D
Controller (U462). Go to Service Group D, paragraph 7-
D-31 for troubleshooting.
failures.
a. Overload, Constant Zero, Floating, or Noisy
Readings. Any one of these failures can be caused by
the A/D Converter or the 3478A's Input Circuitry (Input
Switching or DC/Ohms Input Amplifier).
circuitry can cause a failure, a procedure to isolate the
circuitry is in both Service Group D and Group A. For a
definition of the failures, go to paragraph 7-30 (DC Volts
Failures).
b. A/D Slope Error. This failure can be caused by
the A/D Converter or the A/D Controller and shows up as
an "A:D SLOPE ERR", after a Self-Test routine.
c. A/D Test Fails. This failure can also be caused
by the A/D Converter or the A/D Controller. It shows up
as an "A:D TEST FAIL", after a Self-Test routine.
d. Input Hybrid (U102) Failure. Since the Input
Hybrid receives its set up information from the A/D
Controller, the controller can cause the hybrid to fail.
7-35. Isolation Circuit Failure (Service Group D).
This failure will normally show up as an "A:D Link Fail"
(after the 3478A's Self-Test routine). The failure can be
caused by the Isolation Circuitry, or either the Main
Controller (US01)
Troubleshooting information is in Service Group D,
paragraph 7-D-44.
7-36. Power
Troubleshooting (Service Group E). Service Group E
has some information on how to troubleshoot the power
supplies and Reference Circuitry.
TM 11-6625-3071-14
The following explains the
Since both
or A/D Controller
Supplies and Reference
(U462).