A3 Display Processor Assembly-Level Troubleshooting; A3 Display Processor Assembly-Level Troubleshooting; Equipment Required; Procedure - HP 8340B Manual

A3 Display Processor
Assembly-Level Troubleshooting
EQUIPMENT REQUIRED
Oscilloscope
100
MHz
PROCEDURE
1.
Connect the oscilloscope ground to
GROUND (TP10)
and check the
-5.2V
(TP11).
+5.2V(TP13)
and 4-12V (TP14) supplies for proper voltages.
2.
If the supplies are correct, refer to Figure
G-4 and
remove the front panel, separate the
display
assembly from the keyboard, and reattach the keyboard to
the frame.
3.
Remove
eight screws from the display assembly that
hold the A3
display
processor. Turn the
display processor
over and reinsert the other end of
P1 through P5
into
the same sockets they
came out of. Install two screws to
hold
it in
place.
4.
To
place the display
into the self-test mode, press
[SHIFT] [FREE RUN].
Display RAM
Test Fails
1.
Replace A3U1.
Display Checksum is
Not Equal to 3A
1.
The display checksum
is
shown
in the
ENTRY display during the front panel diagnostics. Press
[SHIFT] [FREE RUN]
and determine
if
the checksum is
equal to 3A.
If
not,
replace A3U1.
Numeric And ENTRY Displays Are Dim
1.
Using an oscilloscope, check the display supply voltage
(A3P5 pin 1,2).
This voltage should be
4.0V
with
430 Hz 0.6V
P-P ripple.
If
this voltage is
low
(<
3.2V), the displays are likely
to
be dim;
if
this
voltage is less than about 2.0V the displays
will be
blank.
If this
voltage is
not correct, the
trouble is
in
the A3 display supply.
Both Numeric and ENTRY Displays are Blank
1.
Check LRESET (A3TP12)
and
CLR (A3P1
pin 1).
If
either
is low, the trouble
is in
the A3 preset
circuitry.
2.
Using an oscilloscope, check the display supply voltage (A3P5 pin
1).
This voltage
should be 4.0V
with 430 Hz 0.6V P-P
ripple.
If
this voltage is
low
(< 3.2V), the displays are
likely to be dim; if
this
voltage Is
less than 2.0V the displays will
be blank.
If
this
voltage
is not correct, the trouble is in the
A3
display supply.
3.
If
both
LRESET
and
CLR are
high,
and the display supply voltage
is
4.0V
or greater, proceed to All
Numeric Displays are Blank,
and
ENTRY
Display is Blank troubleshooting procedures.
G-8 A3 Display
Processor Assembly-Level Troubleshooting
HP 8340B/41B