Maintenance
7-11
7.7
Troubleshooting
The troubleshooting information contained in this section is
intended for qualified personnel having a basic understand-
ing of analog and digital circuitry. The individual should also
be experienced at using typical test equipment, as well as or-
dinary troubleshooting procedures. The information present-
ed here has been written to assist in isolating a defective
circuit or circuit section. Isolation of the specific component
is left to the technician. Note that schematic diagrams and
component layout drawings, which are an essential aid in
troubleshooting, are located at the end of Section 8.
WARNING
The electrometer board shield is con-
nected to the inner shield of the triaxial
input, which is connected either to ana-
log common (unguarded) or guard
(guarded). Thus, the shield can float up
to ±800V above chassis ground.
7.7.1 Recommended test equipment
Success in troubleshooting complex equipment like the
Model 6512 depends not only on the skill of the technician,
but also relies on the use of accurate, reliable test equipment.
Table 7-6 lists the minimum recommended equipment for
troubleshooting the Model 6512. Other equipment such as
logic analyzers and capacitance meters could also be helpful,
especially in difficult situations.
7.7.2 Power-up self-test
Upon power up, the Model 6512 will automatically test
RAM memory and check for proper calibration constants. If
a RAM memory error occurs, the following message will re-
main on the display:
r.r.
If a RAM error occurs, the instrument will be completely in-
operative, and you should assume that a problem exists with-
in the instrument. The problem should be rectified before
using the instrument.
If a calibration error occurs, the two exponent decimal points
will flash. The instrument will be functional under these con-
ditions, but the instrument is probably out of calibration, and
measurements will not be accurate. Use the calibration pro-
cedures in paragraph 7.4 of this section to calibrate the in-
strument. Note that this error may also indicate a defective
NVRAM.
7.7.3 Self-diagnostic program
The self-diagnostic program can be used to test the front pan-
el LEDs, access the firmware revision level, and enter a spe-
cial mode to allow signal tracing through the instrument.
Enter the diagnostic program as follows:
1. Turn off the instrument for at least three seconds if it is
presently turned on.
2. Press and hold the TRIG button, and then turn on power.
3. The instrument will then turn on all front panel LEDS
and display segments. The instrument will remain in this
configuration as long as the TRIG button is held in. The
display should appear as follows:
-1.8.8.8.8.8.8.
4. The software revision level will then be displayed when
the TRIG button is released. A typical example is:
A1
Note that the revision level of your instrument may be
different.
Table 7-6
Recommended troubleshooting equipment
Equipment
Application
DMM with 0.015% basic
accuracy, 10M
Ω
input
impedance (Keithley Model
197A or equivalent).
Dual-trace, triggered sweep
oscilloscope, DC-50MHz
bandwidth.
Power supply and DC
voltage checks; analog
signal tracing; continu-
ity; static logic levels.
Digital and analog wave-
form checks.
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