Power Supplies Troubleshooting; Inguard Power Supplies - HP 3456A Operating And Service Manual

I·F·l. GENERAL.
8-F·2. This Service
troubleshooting information and the 3456A's Internal
Adjustment Procedures. Use the Adjustment Procedure
if components have been replaced in the instrument.
Also. use the procedure that applies to the circuitry in
which a component was replaced (e.g. ACV Adjust­
ment, AC Converter). The following lists the circuitry
and corresponding adjustment procedure.
Cll'tullry
Reference
AID Converter
Input Switching
Input Amplifier
IOOV DC Input
Ohms Current Source
AC Converter
250 kHz Circuitry
The ad justment procedures in this Service
Group does not have to be per f ormed at the
J456A 's normal calibration time.
should only be per f ormed Qjter repairing the
instrument.
The J456A should be on at least one hour
with covers in place and at its operating
temperature, before doing any adjustments.
H·3. POWER SUPPLIES TROUBLESHOOTING.
8-F-4. There are two groups of Power Supplies in the
34S6A, Outguard and Inguard. The Outguard Supply
consists of a single + SV supply. The Inguard Supplies
consists of a + 33V raw supply and + l SV, - I SV,
- J8V, and +SV regulated supplies. The following
paragraphs have the troubleshooting information for
both Inguard and Outguard Power Supplies.
a150
8-F-S . In addition to the Inguard Power Supplies, the
AlO board has various 2V supplies. These supplies
are used to bias comparators used in the Input Switch­
ing, Input Amplifier, AID Convener, and Ohms Cir­
cuitry. The supplies consists of a simple voltage divider
(
used to divide the + S V power supply down to + 2V.
Each of the circuitry, except the Input Switching, have
their own supply. The Input Switching uses the supply
for the Ohms Circuitry. Since either circuitry can load
SERVICE GROUP F
Group has Power Supplies
Procedure
Adjustment
Reference Adjustment
AID Adjustment
DCV Adjustment
OCV Adjustment
lOOV Adjustment
Ohms Adjustment
ACV Adjustment
250 kHz Adjustment
NOTE
They
NOTE
down the supply, the Input Switching can be isolated
from the Ohms Circuitry
A20JMPRI03.
B·F·B. Outllulrd Powlr Supply.
An
8-F-7. Outguard Power Supply fa ilure can
caused by the supply itself (UI, A3CRS through CR8)
or by a shorted Integrated circuit on the A3 or A4
board. Since part of the power supply is located on the
A3 board, the A4 board is the only board that can be
isolated. To do that, remove the A4 board. If the supply
is good ( + 4.7SV to + S.2SV), check for a shoned IC on
the A4 board. If the supply is still i n operative, make
sure A3CRS through CR8 and zener diode CRI are
good. If they appear good, replace UI (mounted on the
chassis near Tt). If still inoperative, check for a
shoned IC on the A3 board.
B·F·B. Ingulrd Powlr Supplill.
8-F-9. Failures in the Inguard Power Supplies can be
caused by the supplies themselves or by shoned com­
ponents in the Inguard. To troubleshoot a supply, do
the following:
a. Determine which supply fails.
b. Turn the 34S6A Ofr.
c. Refer to Table 8-F-1 to determine which board
uses the inoperative supply and where to measure the
various supplies. Remove the board(s) that use the in­
operative supply.
Ylbl, a·F·1. Inglllrd POWIf Supply Location
+33V
Al0P15 Pin 7
+ 15V
Al0P15 Pin 6
- 1 5V
Al0P15 Pin 3
+
5V
Al0P15 Pin 4.5
- lBV
Al0P15 Pin 2
d. Turn the 34S6A On.
e. If the power supply
troubleshoot the supply by doing the following:
J . Measure the voltages and ripple on the raw sup­
plies. The voltages and ripples should be checked
with the regulated supply loaded. The nominal
voltages, ripple, load resistor value, etc. are listed
in Table 8-F-2.
by lifting jumper
be
•.
..... .. .....
A20
A20,A40
A20.A40
A20,A30,A40
A20
is still inoperative,
8-F-l