TUNING THE HEADSTAGE
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125
Chapter 11
Turn switch 1 of SW8 (near center of PC board) to OFF.
Find reset transient on scope (see Figure 25a).
Turn switch 1 of SW8 to ON.
Trim RT22 (TAIL TAU) and RT23 (TAIL MAG) to minimize transient
Internal Reset
Remove pulse generator from Axopatch 200B.
Connect PATCH-1U model cell in PATCH position to headstage.
Set FILTER to 10 kHz.
Adjust PIPETTE OFFSET for zero current.
Set HOLDING COMMAND to 200 mV (toggle set to x1).
Switch HOLDING COMMAND between + and -.
The INTEGRATOR RESET LED should be flashing about twice a second at either
+ or -200 mV.
If there is an obvious time difference between + and -, trim RT24 (CHG INJ) to balance it
out.
Set switches 3,4 and 5 of SW8 to OFF (internal reset compensation).
Find reset transient on scope. It should have about a 2-7 pA amplitude with an apparent
decay time constant of roughly 0.5 ms (see Figure 25b). The transient should be riding on a
DC level of + or -20 pA and should change polarity with DC level.
Set scope to AC coupling 0.5 V/div, 1 ms/div.
Set switch 3 of SW8 to ON.
Trim RT18 (DIAB-1 MAG) and RT19 (DIAB-1 TAU) to eliminate fastest portion of
transient as in Figure 25c.
Switch HOLDING COMMAND between + and - and find a the best possible compromise.
There will be some amount of unavoidable asymmetry.
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