Maintenance; Trouble Shooting - Keithley 610 Manual

SECTION VI MAINTENANCE
No periodic maintenance is required other than checking the accuracy
of the polarization potentials and the high megohm resistors as pro-
vided for by the front panel controls. There are no internal bat-
teries. The method of performing these checks is outlined in
Section IV part E and F.
The calibration of the voltmeter is set by R179 located on the vertical
chassis carrying the majority of ths tubes. This is set at the factory
and should not require adjustment. If recalibration is performed, an
accurate voltage source should be used.
A.
Trouble Shooting
The circuit is completely described in Section III. Study of that
section will facilitate any trouble shooting.
The most usual trouble encountered is that on the most sensitive volt-
age range, with the input shorted, it is not possible to bring the
meter pointer to zero.
However before assuming that the instrument is
at fault make surs that resetting the COARSE BAL control at the rear of
the instrument will not bring the instrument back into balance.
If
this does not work remove the instrument case and if necessary the
bottom plate just below the input compartment to gain access to all
circuitry. Follow this procedure:
(1) Check for presence of regulated B-plus voltage by switching
the meter to TESTC225v. If this voltage is not correct consult .
section following on servicing regulated power supply.
(2) If correct voltage is present, check the plus and minus 220
volt supplies which supply the output cathode follower. The plus
voltage is present on pin 3 of V5.
The minus voltage may he ob-
tained from the bottom of the 30k cathode resistor of V5-B. It
is a 10 watt power resistor located on the metal chassis next to
the rectifier stacks. If this voltage is not correct consult the
schematic and trouble shoot the supply in the usual manner.
(3) If no defects are found so far , proceed by shorting floating
ground to output ground to remove the negative feedback. This is
most conveniently accomplished by shorting the two ends of the
FAST-NORMAL switch on the rear panel. In this condition the in-
strument will become very sensitive and in operating the ZERO
control, the meter will be very difficult to hold on scale. How-
ever, the indication that the circuit is operating satisfactorily
is that it is possible to swing the voltage through the correct
operating point as indicated on the voltage-resistance diagram.
VI - 1