8
•
FUNCTIONAL CHECKOUT
Axopatch 200B, Copyright 1997-1999, Axon Instruments, Inc.
larger and longer lasting. Turn on the WHOLE CELL CAP. switch. Using the
SERIES RESISTANCE and WHOLE CELL CAP. controls, observe a change in shape
and size of the capacitance transients. The capacity transient must be nulled to read
correct values of the membrane capacitance (C
m
) and the series resistance (R
s
) from
these front panel controls.
17) Without completely nullifying the transient, turn on the % PREDICTION control and
rotate it clockwise. Observe the capacitance transient getting larger and faster.
18) Now switch off the WHOLE CELL CAP. and turn the SERIES RESISTANCE control
to about 10 MΩ. Set the LAG control to its maximum value and then turn on the %
CORRECTION control. Rotate this to the right and again observe that the capacitance
transients get larger and faster. Set the control to 100%. Rotate the LAG control
counterclockwise and verify that the circuit will oscillate at lower LAG values.
Test CAPACITANCE DITHER:
19) Set up as in 15 and 16 above. Connect square-wave voltage source (switching from
approximately 0 V to +5 V at a frequency of between 0.5 to 5 Hz) to CAP DITHER
CONTROL BNC connection on back panel. Set lowpass filter setting to 100 kHz.
View transients on oscilloscope screen. Note small changes in compensation as dither
unit is activated by square pulses from square wave voltage source. These changes will
be very small and may require sensitive adjustment of gain and triggering on the
oscilloscope.
Test ZAP:
20) Turn off SEAL TEST, PREDICTION & CORRECTION. Set the ZAP control to
MANUAL and set the METER to I. While the ZAP button is depressed you should see
a reading of approximately +2.6 nA.
21) Set the ZAP control to 0.5 ms. Depress the ZAP button several times. The OVLD
light in the SCALED OUTPUT section should flash each time the button is pushed.
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