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Maintenance
7.3
Line fuse replacement
A rear panel fuse protects the power line input of the instru-
ment. Use the following procedure to replace the line fuse:
WARNING
Disconnect the instrument from the
power line and other equipment before
replacing the fuse.
1. With the power off, place the end of a flat-blade screw-
driver into the slot in the rear panel LINE FUSE holder.
Push in gently, and rotate the fuse carrier one-quarter
turn counterclockwise. Release pressure on the holder,
and its internal spring will push the fuse and carrier out
of the holder.
2. Remove the fuse, and replace it with the type recom-
mended in Table 7- 2.
CAUTION
Do not use a fuse with a higher current
rating than specified, or instrument
damage may occur. If the instrument re-
peatedly blows fuses, locate and correct
the cause of the trouble before replacing
the fuse.
3. Install the new fuse and the fuse carrier into the holder
by reversing the above procedure.
Table 7-2
Line fuse selection
Line voltage
Fuse type
90-125V
A, 250V, 3AG,
slow blow
195-250V
1
⁄
A, 250V, 3AG,
16
slow blow
7-2
Keithley part no.
FU-20
FU-21
7.4
Calibration
An advanced feature of the Model 6512 is its digital calibra-
tion capabilities. Instead of the more conventional time-con-
suming method of adjusting numerous calibration potentio-
meters, the technician need only apply an appropriate cali-
bration signal and digitally calibrate the instrument, either
from the front panel, or over the IEEE-488 bus.
7.4.1 Calibration cycle
Calibration should be performed every 12 months, or if the
performance verification procedures in Section 5 show that
the instrument is out of specification. If any of the calibration
procedures cannot be performed properly, refer to the trou-
bleshooting information in this section.
7.4.2 GUARD switch
Place the V, Ω GUARD switch in the OFF position unless
otherwise noted.
7.4.3 Calibration jumper
A jumper, located in the mother board, disabled/enables
front panel and IEEE- 488 bus calibration. When the jumper
is in the disabled position, permanent (NVRAM) storage of
calibration constants will not take place. However, tempo-
rary calibration values may be entered and used even if
NVRAM calibration storage is disabled. Note, however, that
calibration parameters will be lost once power is turned off
unless they are stored in NVRAM.
The calibration jumper location and the disabled/enabled po-
sitions are indicated in Figure 7-1.
WARNING
Turn off the instrument, and disconnect
the line cord before removing the top cov-
er to reposition the calibration jumper.
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