HP 3478A Technical Manual page 138

e. If any signatures are incorrect, U501 may be at
fault. Replace U501. If all signatures are correct, the
keyboard can be checked by doing the following:
1. Leave the Signature Analyzer connected
as in step c.
2. By pressing a certain front panel button,
the signature on a port of U501 should change. For
example, the signature on U501 pin 27 (port P10)
should change from "P6H5" to "U878", if the a button is
pressed. From this change, it can be determined if the
button (i.e., part of the keyboard) is inoperative or good.
The following lists the pin numbers of U501, the button
to be pressed, and the change in signature.
7-D-17. HP-IB Failure
7-D-18. Before troubleshooting for inoperative HP-IB,
make sure the 3478A is operating correctly from the
front panel. Repair the front panel operation first, before
troubleshooting for an Hp-IB failure. To troubleshoot an
HP-IB failure, go to Flowchart C. The procedure in the
flowchart checks the HP-IB Chip to determine if data
can be written to or read by the chip.
7-D-19. U.C. ROM Fails
7-D-20. If the "U.C. ROM FAIL" message is displayed
(during a Self-Test routine), the most likely cause is a
failure in Control ROM (U502). To make sure the ROM
is defective and not the Main Controller, go to Flowchart
A (see paragraph 7-D-11) for troubleshooting.
7-D-21. U.C. RAM Fails
7-D-22. If the "U.C. RAM FAIL" message is displayed,
the failure is most likely in the Chassis Common CPUs
RAM (RAM in Main Controller U501). To make sure the
RAM is defective, go to Flowchart A (see paragraph 7-
D-11) for troubleshooting.
7-D-23. Calibration RAM Failure
7-D-24. If the "CAL RAM FAIL" message is displayed
(after a Self-Test routine), the most likely cause is a
Calibration RAM (CMOS RAM, U512) Failure.
RAM can be checked by sending data to the RAM and
reading it back.
Make sure grounded tools and wrist
straps are used, when replacing or
checking the display.
The test in paragraph 7-D-24 cannot be
made without destroying the present
data in the Calibration RAM. The 3478A
must be recalibrated, after doing the
test.
a. Turn the 3478A off.
b. Move jumpers JM502 and JM503 to the "D:
position.
c. Connect and set the Signature Analyzer as
follows:
d. Turn the 3478A on and check the following
signatures.
U512 pin 9: H709
U512 pin 11: C577
U512 pin 13: 4296
U512 pin 15: 8U25
e. If any signatures are wrong, something on the
Data Bus is defective. Go to Flowchart A (see
paragraph 7-D-11) for troubleshooting.
f. If the signatures are good, the RAM (U512) may
be defective. The RAM can be checked by continuing
with the test in the next step.
7-D-4
TM 11-6625-3071-14
CAUTION
CAUTION
The