Teledyne 514 Instruction Manual page 59

Maintenance & Troubleshooting 5.0
2. When the log amplifier integrated circuit A1 is replaced on the
chopper stabilized log amplifier circuit card, it is necessary to re-
adjust potentiometers R10 and R11 in order to balance the circuit.
You should have on hand an extender card to help make
connections accessible, one 20K ohm resistor, and a high
impedance voltmeter.
a. Temporarily connect a 20K resistor (stable, not
composition type) between A1-2 and A1-7, across C2.
b. Unplug A2, A3, A5, and A9.
c. Jumper A5-7 to A5-5 at the socket and A2-3 to A2-6 at
the socket.
d. Install the card in the card extender and turn on the
analysis unit power.
e. Verify that voltage to pin 7 of the card edge connector is
approximately 9 volts. Measure between pin 7 and pin
14.
f. Adjust potentiometer R10 until the voltage measured at
A1-7 is zero with respect to signal common TP3
g. Remove jumpers installed in step c.
h. Remove resistor connected in step a.
i. Set R34 to give 9 volts on A9-6. Also set R34 to give 9
volts on A9-14.
j. Remove Q1 from its socket.
k. Disconnect connector pin 7 from input by lifting a
connection on the extender card.
l. Temporarily connect a 20K resistor between A5-7 and
A5-15 to A1-16.
m. Jumper between A9-6 and A5-7 to provide the 9 VDC
through 20K into A1-2 and through 20K into A1-16.
n. Adjust potentiometer R11 until the voltage measured at
TP2 is zero.
o. The log amplifier integrated circuit A-1 is now balanced.
p. Remove the 20K resistor and the jumper. Restore
connections and replace IC's. Turn on the instrument
power and check the control loop by measuring voltage at
the output of A2. Voltage should be -3 VDC, nominal.
q. If voltage is positive, R11 is out of balance or a
component in the loop has failed. A slight adjustment of
R11 should cause the voltage to change polarity. After
checking this go back to the nominal -3 VDC by
adjusting R11.
Teledyne Analytical Instruments
A Business Unit of Teledyne Electronic Technologies
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