HP 3465B - Troubleshooting and Circuit; Diagrams; Introduction; Schematic Diagrams

Model 3465B
Section VII
SECTION VII
TROUBLESHOOTING AND
CIRCUIT DIAGRAMS
7-1. INTRODUCTION.
7-2. This section of the manual contains troubleshooting
information, the functional block diagram and circuit
diagrams for the Multimeter. The troubleshooting para
graphs are divided into three parts:
a. Preliminary troubleshooting
b. Analog troubleshooting
c. Digital troubleshooting
Additional troubleshooting information is located on the
block diagram and individual circuit diagrams in the form
of dc voltage levels and notes.
7-3. SCHEMATIC DIAGRAMS.
7-4. The schematic diagrams (Figure 7-2 through Figure
7-5) contained in this section illustrate the circuits of the
Multimeter. Components marked with an asterisk are those
that are critical in value. Some of these "starred" compo
nents are part of an adjustment procedure. A method for
selecting the correct value is outlined in the adjustment
procedures of Section V, if service in these circuit areas is
required.
WARNING I
Maintenance procedures of Sections V and VII
are intended for qualified service personnel
only. To reduce the possibility of electrical
shock, only qualified personnel are to perform
maintenance duties.
7-5. PRELIMINARY CHECK.
7-6. Visual Inspection.
1-1. Record all observances of all function and range mal
functions. Verify that the leads interconnecting the input
jacks with the A1 board are securely fastened at both ends.
Look for obvious cracked, broken, or burned comnonents.
7-8. PRELIMINARYTROUBLESHOOTING.
7-9. Providing the functional check mentioned in the pre
vious section has been performed, the tests of this section
may be unnecessary. This would be the case if the fault is
unique to any function, range or combination thereof
treated in the Signal Conditioning Section. It should be
obvious that if the fault is uncommon to all functions, the
Signal Conditioning block is probably the culprit. An
exception would be a problem in the switch contacts
located in the A/D converter.
7 10. If the malfunction is common to all functions the
fi rst check is to verify the operation of all Power Supply
voltages. The only critical supply in terms of tolerance is
the -t 10 V. If the multimeter's accuracy is out of specifica
tion across all functions, check the -t 10 V and adjust if
necessary. See the Power Supply Adjustment section of the
manual. If any of the supplies are inoperative, go to the
Power Supply section of this guide.
7-11. Analog/Digital Isolation.
7-12. If the supplies are proper, place the meter in the 2 V
dc range. Connect a jumper from pin 7 of JI (the number
I end is identified with a dot on the PC board) to the CP
test point (next to the crystal). The display should read
-H 1.0000. If it does not, the fault is in the Control Logic,
Display Interface or Display. Go to the Digital Trouble
shooting section. If the display is proper, remove the
jumper and go to the Analog Troubleshooting section.
7-13. ANALOG TRDUBLESHOOTING.
7-14. Analog Isolation.
7-15. It should be mentioned here that if the problem is
unique to any function, that particular portion of the signal
conditioner should already have been cleared. If the mal
function is common to ac and dc volts or common to the
ac volts and ac current, refer to the Signal Conditioning
Section.
7-16. With the instrument still in the 2 V dc range, short
the input and monitor the voltage at the DCTP terminal.
The voltage should be less than I mV. Now apply -t I V dc
to the input and monitor the same point with an oscillo
scope. The waveform should look like the following:
IV-
H
O.ls
^ 0«3i •
If either of these stipulated conditions are not met, the
fault is probably in the input amplifier. A further check of
the input amplifier is to vary the input voltage level. The
peak value of the rectangular wave should follow the input.
7-1