Keithley 610C, Инструкция по эксплуатации

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TABLE 7.
Model 6l0C Troubleshooting.
Difficulty Probable Cause
Solution
Excessive zero offset
Input transistors may be defec-
Check QIOI and Q102; replace if
tive. faul ty.
Excessive offset current Excessive temperature fluctuation Check QI01 and QI02; replace if
or defective input transistors. faul ty.
Cannot meter zero on any range.
See paragraph 5-5.
See paragraph 5-5e, Step 7.
Unable to zero meter on most
Incorrect base voltage on input
Check per paragraph 5-5.
sensitive range. transistors.
Meter will not" zero on one
Faulty resistor for setting of Check resistors; replace if faul ty.
Multiplier Switch setting. Multiplier Switch.
10-10 to 10-14 ampere curren t
Defective high megohm resistors. Check per paragraph 6-10.
ranges are out of specification.
5-4. TROUBLESHOOTING.
a. The procedures which follow give instructions
for repairing troubles which might occur in the Model
6l0C.
Use the procedures outlined and use only speci­
fied replacement parts. Table 6 lists equipment rec­
ommended for troubleshooting. If the trouble cannot
be readily located or repaired, contact Keithley In­
struments, Inc., or its representatives.
b. Table 7 contains the more common troubles which
might occur. If the repairs indicated in the table do
not clear up the trouble, find the difficulty through
a circuit-by-circuit check, such as given in paragraph
4-5. Refer to the circuit schematic to find the more
critical components and to determine their function in
the circuit.
The complete circuit schematic, 22821E,
is in Section 7.
5-5.
PROCEDURES TO GUIDE TROUBLESHOOTING.
8.
If the instrument will not op�rate, check the
fuse, line cord and power source. If these are found
satisfactory, use the following procedures to isolate
the trouble.
b. The schematic diagram indicates all transistor
terminal voltages referenced to either floating ground
or output ground; a properly operating Electrometer
will have these values =10%.
The control settings for
these values are the Range Switch at VOLTS, Multiplier
Switch at
1,
and the meter zeroed. Measurements are
with the Model 153.
c. At times, the meter will not zero on any range
with the input shorted. Adjust the COARSE ZERO Switch,
Sl02 (Figure 2), to bring the Model 610C into balance.
If this does not work, continue to check the circuits.
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d. Power Supply.
1. Check the plus and minus 120 volt supplies
with a Model 160 DVM and a Model 561A Oscilloscope
to within 10% of the indicated schematic value.
a) Vary the line voltage from 105 to 125 volts
for a 117 volt line and from 210 to 250 volts for
a 234 volt line. The ±120 volt supplies should
change by less than 2 volts. Return the line
voltage to nominal value.
b) The ripple on the z120 volt supplies should
be less than 40 mV peak-to-peak. If the ripple
is high (up to approximately 0.3 volts peak-to­
peak), check the output noise on the 1 millivolt
range before attempting any corrective action.
If
the noise is within specification, 90 mV rms, the
high ripple is acceptable.
If the noise is out of
speCifications, try replacing the applicable zener
diode to reduce ripple.
c) If replacing zener does not correct the high
ripple, the probable cause is high beta in Qlll
and/or Ql12.
Select for a beta range of 35-80.
d) High ripple on the ... 120 volt supply may also
be due to a defective 01]4 diode in the center
zero circuitry.
e) Line transients (spikes) may or may not be
present depending upon machinery in operation at
the time.
2. Check the plus and minus 9 volt supplies in
the same manner on the ±120 volt supplies.
The
ripple for the ±g volt supplies must be less than
4 mV peak-to-peak.
e.
1.
To check the amplifier, disconnect the feed­
back loop by removing the complimentary input tran­
sistors QIU and Q1l2.
This allows each stage of the
amplifier to be individually checked. It also elim­
inates the possibility of applying excessive voltagA
to the input transistors, causing serious damage.
2. Connect the Model 153 between the drains of
QIOI and QI02. Adjust the COARSE and MEDIUM ZERO
Controls for null. If a null cannot be reached,
check QIOl, QI02, the COARSE and �DIUM ZERO Control
circuits (resistors R1l4 to R135), and transistors.
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