Outguard Isolation Logic - HP 3456A Operating And Service Manual

Model 3456A
3456A's Outguard can be half-split. This can be done by
c
replacing the A3 board with a good one. If the Data
Lines are good, the A3 board is bad. I f the Data Lines
are still bad, the A4 board is bad.
8-A-3!. If a good A3 board is not available, do the
following:
a. Turn the 3456A Off.
b. Remove the A4 board and isolate it from the
chassis.
c. Connect pin I of P6 to the A4 board's 5V test
point.
d. Connect pin 3 of P6 to the A4 board's GND test
point.
e. Connect pin 10 of P6 to pin 10 of A4J5.
f. Turn the 3456A On.
Make sure the A4 does not touch any o f the
3456A 's chassis or components while the in­
strument is turned on, or damage to (he
board may result.
Make sure the 3456A i s turned O f f when
removing or re placing a printed circuit
board, or damage may result to the instru­
ment and board.
8-A-32. If the Data Line signatures are now good, the
A3 board is bad. If the signatures are still bad, the A4
board is at fault.
8-A-33. Once it has been determined which board is at
fault, determine which Integrated Circuit on the Data
Bus is causing the bad signature. Most of the Integrated
Circuits on the Data Bus, except for the RaMs, can be
removed without affecting SA. Some possibilities are:
a. A4 Board: Try replacing the RAMS. A4US. U I 2
and associated circuits. Next try the Display Latch.
A4U28, and Keyboard
possibilities are the RaMs, A4U5, U7, and US.
b. A3 Board: Remove the HP-IB chip A3U9. If that
does not help, try Address Buffer A3U16, and Isolation
Logic Transmitter and Receiver Registers A3UIO, U20.
8·A·34. OUTGUARO ISOLATION LOGIC.
B·A-35. General.
8-A-36. The Outguard Isolation Logic can be defective
if only dashes (- - - - - -) are displayed. Since this is also
true if the 3456A has an Inguard Failure, determine the
failure by doing the following:
a. With the 3456A turned On. press the TEST but­
ton.
Buffer. A4U25. Other
b. I f Test 113 fails ( - 3 .00000 displayed). the 3456A
has an Isolation Logic Failure. Continue with Step d .
+ S."
c. I f + 1.8.S.8.S.S.
. .
(Test 113 does not fail), the Byte Available Line (A3U17.
pin 9) may be held High or Low. Make sure the line and
pin 1 0 of U I 3 toggles. If pin 1 0 of U I 3 is toggline and
the Byte Available line is not, replace U17. If pin 1 0 of
U I 3 is not toggling, replace UI3.
d. Turn the 3456A Off.
e. Unplug the cable from the Isolation Logic Connec­
tor (A317).
f. Connect pin 1 to 2 and 3 to 4 on the Isolation Logic
Connector. If the Isolation Logic Test Jumper. -hp-Part
No. 03456-61602 is available, plug it into 17 instead of
shorting the pins.
g. Turn the 3456A On.
h. Press the TEST button and then set the 3456A to
Test 113 by pressing the 3 , STORE, and 5 (COUNT)
keys.
i. If Test 113 still fails, the Outguard Isolation Logic is
at fault. Go to the next paragraph. I f the test passes
( + 3.00000 displayed), the Inguard Isolation Logic is at
fault. Go to Service Group B for troubleshooting.
B·A-31. Isolating the Transmitter from the Receiver.
8-A-3S. The Isolation Logic Failure can be either in the
Transmitter or Receiver Circuitry. To determine which
circuit is at fault do this:
a. Make sure the 3456A is still sel-up for Test #3 and
the Isolation Logic Connector's pins are shorted.
b. Connect the vertical input of an oscilloscope to the
core of transformer A3Tl. Using the scope set-up infor­
mation in Figure 8-A-7A, check for the waveform
shown in the figure.
. I V
5 Jlsec
B
. 1 V
2 Jl sec
Pos. Trig.
figure B·A·7. Trensmitter Output
Service
i s constantly displayed
A
Pos. Trig.
c
1
-"sec Pos. Trig.
Rev B 8-A-17