HP 3478A Technical Manual Download

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TM 11-6625-3071-14

3478A

make sure the CPU’s clock (at pin 2 and 3 of USO1) is at
approximately 5.856MHz. Try replacing crystal Y501 and
if the signal is still missing, try U5O1.

Figure 7-D-1. U501 ALE Signal

c. Make sure the RESET line at pin 4 of US01 is high. If
the line is low, try replacing USSO (see Schematic 4).
7-D-9. Turn-On Failure

7-D-10. The Turn-On Failure normally shows up if all of
the following symptoms are noted. If only one symptom
is noted, it is not a turn-on failure. The symptoms for a
turn-on failure are as follows:

The display is dead or inoperative. Since this

can also be caused by a defective display, assume it is
turn- on failure before troubleshooting the display.

The keyboard is inoperative (does not respond).

If only the keyboard is inoperative, go to paragraph 7-D-
15 for troubleshooting.

HP-IB is inoperative. It may not be necessary to

check for an HP-IB failure if the two previous symptoms
were are noted. If only an HP-IB failure is noted, go to
paragraph 7-D-17 for troubleshooting.

7-D- 11. If the previous symptoms were noted, go to
Flowchart A for troubleshooting. In the Flowchart, the
various address lines and data lines are checked, using
Signature Analysis, to determine the faulty component.
The faulty component(s) can be the Main Controller
(USOI1), Control ROM (U502), CMOS RAM (U512), or
the HP-IB Chip (U503).
7-D-12. Before troubleshooting for a Turn-On Failure,
check the following:

Make sure the Data Bus Break E527 is making

good contact. If the pins are bent, the signatures on the
Data Lines may be good, but the 3478A may be in-
operative.

Make sure jumpers JMS01, JM502, and JM503

are in the "N" (Normal) position. The 3478A will not turn
on at all or properly, if they are in a different position.

7-D-13. Inoperative Display
7-D-14. An inoperative display is when all or part of the
display is inoperative. The failure can be caused by the
display itself or part of the Chassis Common Circuitry.
Before doing any troubleshooting, make sure the 1. IV,
2.2V, and 3.3V power supplies to the display are good.
The supplies can be checked at R503 pins 9, 3, and 15
for the 3.3V, 2.2V, and 1.IV power supplies, respective-
ly. If any supply is wrong, replace R503 and if still wrong,
replace the display. If the supplies are good, go to
Flowchart B for troubleshooting. In the Flowchart, the
control lines to the display are checked, using Signature
Analysis routines, to determine if the display or another
circuit is at fault.

Make sure grounded tools and wrist straps are
used, when replacing or checking the display.

7-D-15. Inoperative Keyboard

7-D-16. An inoperative keyboard is when all or part of
3478a operations cannot be selected from the keyboard.
This can be caused by the keyboard itself or by the Main
Controller. The following procedure checks the ports of
the Main controller (using Signature Analysis) that
receive the information from the keyboard. From the
resultant signatures it is determined if the keyboard or
the Main Controller is defective. Do the following:

Turn the 3478A off.

Move jumpers JM502 and JM503 to the "D"

position.

Connect and set the Signature Analyzer as

follows:
Start:

TP7.(

)

Stop:

TP8 (

)

Clock:

TP3 (