Linepower; Battery Power; Displayanda/Dconverter; Acconverter - Keithley 177 Instruction Manual

5.6.2
Line Power
In general, start troubleshooting with Table 5-3, line power
checks, to verify that the power supplies are providing the
correct voltages to the electronic components.
5.6.3 Battery Power
If trouble occurs on battery power only, or if battery
operating time is substantially less than six hours after over-
night charging, test the batteries and charging circuit per
Table 5-4.
5.6.4 Display and A/D Converter
Proper operation of the AID converter and display should be
verified before troubleshooting the signal conditioning cir-
cuits. Check the A/D converter and display per Table 5-5 and
5-6, respectively.
5.6.5
AC Converter
Problems with AC voltage or AC current ranges may involve
the AC converter. Check this circuit per Table 5-l. If the pro-
blem is only on AC current ranges, see below.
5.6.6 Chopper Amplifier and Ohms Source
Problems with DC voltage, DC current, or resistance ranges
may involve the chopper amplifier. Check this circuit per
Table 5-8. After verifying chopper amplifier operation by
completing steps 1 through 10 of Table 5-8,
QO
to Table 5-9 if
resistance measurements are erratic. If problem is only on DC
current ranges, see below.
NOTE
Dust, flux or other contamination will degrade
performance on resistance and DC voltage
ranges.
5.6.7 Current Shunts
If problems occur with current readings, check the current
shunts and related circuitry per Table 5-10. It should be noted
that, since the current shunts are common to both AC end
DC current, problems should exist on the same AC and DC
current ranges if there is a fault in the current shunt circuitry.
NOTE
All measurements are referenced to
analog
com-
mon (ground clip), unless otherwise noted in the
Tables.
If a gross failure exists that indicates a possible blown fuse
(line power, battery pack, or current fuse) refer to paragraph
5.8 for fuse replacement instructions.
WARNING
Some procedures in the following tables re-
quire the use of high voltege. Take cere to
prevent contact with live circuits which
could reuse electrical shock resulting in in-
jury or death.
5.7 FRONT PANEL ZERO KNOB REMOVAL AND
REPLACEMENT
The from panel ZERO knob will have to be removed if either
the front panel or display is to be removed. To remove the
knob, proceed as follows:
1, Carefully remove the end-cap (shown in Figure 5-31 using a
thin-bladed instrument.
2. Loosen the slotted screw and remove the knob from the
shaft.
3. Take care not to damage or lose either the end-cap or
knob. These items provide protection against electrical
shock and must be installed when the instrument input is
floating.
NOTE NOTE
If the display board has to be removed for If the display board has to be removed for
troubleshooting or repair, the front panel ZERO troubleshooting or repair, the front panel ZERO
knob will also have to be removed. knob will also have to be removed.
-1.2"
n
I
-,o"-~----~-
I
( 100 ;
,
200
I
100
ImSEC!
/
InSEC I mSEC I
AUTO ShGNA; REFERENC: AUTO ZERO OF !
ZERO INTEGRATE INTEGRATE NEXT CONVERS,ON
Comparstor waveform Logic 1 during ramping)
'L-J-l--
Figure 5-2. Integrator end Comparator Waveforms
WARNING
The ZERO potentiometer shaft is electrical-
ly connected to INPUT LO. Maintain INPUT
LO et ground potential while the ZERO
knob or its cep is removed to prevent en
electrical shock hazard.
5-4