TB 9-6625-2294-35
17. DAC REF and Input Capacitance
a. Performance Check
(1) Connect digital multimeter HI to J119 (fig 1) pin 13 and LO to chassis ground.
(2) Press ∆t pushbutton for a ∆t display on crt.
(3) Rotate ∆ control ccw for a constant, stable digital multimeter value
(approximately -1.25 V dc). Record indication.
(4) Rotate ∆ control cw for a constant, stable digital multimeter value
(approximately 1.25 V dc). Record indication.
(5) Add the absolute values of indications recorded in (3) and (4) above. If sum of
indications does not equal 2.500 V dc, adjust R2010 (fig. 2) for 1.250 V dc or best
compromise on digital multimeter while repeating (3) and (4) above.
(6) Disconnect digital multimeter.
(7) Press ∆t pushbutton to off (no cursors on display).
(8) Connect oscilloscope calibrator SOURCE/MEASURE CHAN 1 to TI CH 1
using a 5-80 pF standardizer.
(9) Set oscilloscope calibrator EDGE, output for 600 mV, at 1 kHz output.
(10) Rotate knob located below EDIT FIELD pushbutton on oscilloscope calibrator
for 6 divisions on TI display.
(11) Adjust 5-80 pF standardizer for a square front corner over the first 40 s (0.4
division) of the positive portion of waveform. Note waveform front corner for use in (14)
below.
(12) Set oscilloscope calibrator EDGE output for 300 mV at 1 kHz.
(13) Set VOLTS/DIV switch to 50 mV and repeat (10) above.
(14) Adjust CH 1 50 mV C ADJ (Cl05) (CH 2 50 mV C ADJ (C205) for CH 2) (fig. 1)
for same waveform front corner as noted in (11) above.
(15) Set VOLTS/DIV switch to 100 mV.
(16) Repeat (9) through (15) above as necessary so no change is observed in the
waveform front corner.
(17) Press VERTICAL MODE CH 1 to off and CH 2 to on.
(18) Press TRIGGER SOURCE pushbutton to CH 2.
(19) Repeat technique of (8) through (16) above for CH 2.
