HP 3478A Technical Manual page 93

7-E-1. INTRODUCTION 7-E-1. INTRODUCTION
7-E-2. 7-E-2. This Serv This Service Group ice Group has in
troubleshoot the 3478A's Power Supplies and Reference troubleshoot the 3478A's Power Supplies and Reference
Circuitry. Circuitry.
7-E-3. POWER 7-E-3. POWER SUPPLY SUPPLY TROUBLESHOOTING
7-E-4. The Floating Common 7-E-4. The Floating Common Section of th
three power supplies which are: + 5V, -15V, and + 15V. three power supplies which are: + 5V, -15V, and + 15V.
The Chassis Common Section has one + 5V supply. The Chassis Common Section has one + 5V supply.
The following paragraphs have some troubleshooting The following paragraphs have some troubleshooting
information for the Chassis Common and Floating information for the Chassis Common and Floating
Common supplies (refer to Schematic 4) Common supplies (refer to Schematic 4)
7-E-5. 7-E-5. Chassis Comm Chassis Common Power
7-E-6. A low supply 7-E-6. A low supply can be caused if zen can be caused if zener diode CR766
and capacitor C762 are shorted, if there is an excessive and capacitor C762 are shorted, if there is an excessive
load on the supply (shorted component in the Chassis load on the supply (shorted component in the Chassis
Common Logic Circuitry), or if regulator U760 is defec- Common Logic Circuitry), or if regulator U760 is defec-
tive. tive. A high supply A high supply can be cause can be caused by U760.
7-E-7. Floating Comm 7-E-7. Floating Common Power
7-E-8. + + SV 7-E-8. SV Supply Supply. . A low supply A low supply can be caused
excess load on the supply, a shorted CR712, or a defec- excess load on the supply, a shorted CR712, or a defec-
tive U701. The supply tive U701. The supply can be checked
JM701. If the JM701. If the supply is st supply is still low, troubleshoo
ly. ly. Otherwise, Otherwise, troubleshoot troubleshoot the Float
cuitry. cuitry.
7-E-9. 7-E-9. A high supply A high supply is most likely caused is most likely caused by a de
tive U701. tive U701.
7-E-10. 7-E-10. + + 15V 15V and and -1SV -1SV Supplies
supp- ly is a mirror image of the + 15V supply, use the supp- ly is a mirror image of the + 15V supply, use the
following following procedure procedure for for both
difference is that the -15V supply has an additional filter difference is that the -15V supply has an additional filter
capacitor C706.) capacitor C706.)
-E-11. A low supply -E-11. A low supply can be caused by can be caused by an excessive load
on the supply, a shorted filter capacitor or protec- on the supply, a shorted filter capacitor or protec-
POWER SUPPLIES AND REFERENCE TROUBLESHOOTING POWER SUPPLIES AND REFERENCE TROUBLESHOOTING
T T i i t t l l e e
Introduction Introduction .........
Power Supply Troubleshooting................ Power Supply
Chassis Common Power Supply Chassis Common Power Supply ...........
Floating Common Power Supplies Floating Common Power Supplies .........
Reference Circuitry Troubleshooting ......... Reference Circuitry Troubleshooting
has information formation used
TROUBLESHOOTING
Section of the 3478A has e 3478A has
on Power Supply Supply
er diode CR766
d by U760.
on Power Supplies Supplies
can be caused by an
can be checked by lifting by lifting jumper
ill low, troubleshoot the supp- t the supp-
the Floating Common ing Common Cir-
by a defec-
Supplies. . Since Since the
both supplies. supplies. (The only (The
an excessive load
SERVICE GROUP E SERVICE GROUP E
Service Group E Contents Service Group E Contents
.................. .................. ..................
Troubleshooting..........................
tion diode, an open temperature sensitive resistor tion diode, an open temperature sensitive resistor
(RT706 or (RT706 or RT707), or
can be checked by lifting jumper JM703 for the + 15V can be checked by lifting jumper JM703 for the + 15V
used to to
supply or jumper JM702 for t supply or
ply is now good, troubleshoot the Floating Common ply is now good, troubleshoot the Floating Common
Circuitry. If still low, Circuitry.
7-E-12. 7-E-12.
regulators (U702 or U703) regulators (U702 or U703)
7-E-13.REFERENCE CIRCUITRY 7-E-13.REFERENCE CIRCUITRY
TROUBLESHOOTING TROUBLESHOOTING
7-E-14. 7-E-14.
develop three reference voltages: + O1V, -IOV, and a develop three reference voltages: + O1V, -IOV, and a
buffered + buffered + O1V.
depends on the + 10OV reference voltage, make sure depends on the + 10OV reference voltage, make sure
the + IOV is good before troubleshooting the other the + IOV is good before troubleshooting the other
reference reference supplies.
to Schematic 3). to Schematic 3).
a. a. If th
following: following:
The voltage should be quiet and at approximately + 7V. The voltage should be quiet and at approximately + 7V.
by an
jumper
Cir-
C431. Measure pin C431.
fec-
and quiet, replace U403. and quiet, replace U403.
the -15V -15V
U405. U405.
only
b. b. If t
noisy, noisy, replace U405.
U403. U403.
7-E-1 7-E-1
P P a a r r a a g g r r a a p p h h
.................. .................. ............ ... ...7-E-1 ...7-E-1
..............7-E-3 ....7-E-3
.................... .............7-E-5 ....7-E-5
.................. ............7-E-7 ...7-E-7
................ .......... ... 7-E-1 7-E-13 3
RT707), or a defective a defective regulator.
jumper JM702 for the -15V supply he -15V supply. . If the sup-
If still low, troubleshoot t troubleshoot the supply.
A high A high supply supply is most likely is most likely caused by
The 3478A' The 3478A's Reference s Reference Circuitry
O1V. Since the Since the -O1V and
supplies. Perform th Perform the following
If the + 10V r e + 10V refe eferen rence is in
1.Measure the voltage at zener diode U461. 1.Measure the voltage at zener diode U461.
2.If the voltage is wrong, replace U461. 2.If the voltage is wrong, replace U461.
3.If the voltage is good, short across capacitor 3.If the voltage is good, short across capacitor
Measure pin 6 of 6 of U405. U405.
4.If the voltage at pin 6 is approximately + 7V 4.If the voltage at pin 6 is approximately + 7V
5.If the voltage is still incorrect or noisy, replace 5.If the voltage is still incorrect or noisy, replace
If the + 10 he + 10V is go V is good an od and the -
replace U405. If still incor If still incorrect or no
TM 11-6625-3071-14 TM 11-6625-3071-14
regulator. The supply The supply
If the sup-
he supply.
caused by the
Circuitry is used is used to to
-O1V and buffered + 10V buffered + 10V
e following checks (refer checks (refer
ce is inope operat rative ive, do th , do the e
d the -10V i 10V is inco s incorre rrect or ct or
rect or noisy, rep isy, replace lace
the