Heathkit Model IT-1121

Semiconductor Curve Tracer

Calibration Procedure

Ancillary Equipment Required

VTVM

20 MHz DC Oscilloscope

MPSA20 NPN transistor (or equivalent)

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INITIAL RESISTANCE CHECKS

Refer to Figure A

Manual page 50

(    )         Set the VTVM FUNCTION switch to the OHMS position.

(    )         Set the VTVM RANGE switch to the R x 100 position.

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· Test points are on the foil side of circuit board [back panel looking forward] (see Figure A).

(    )         Adjust the SWEEP VOLTAGE control (SW1) to the OFF position.

(    )         Connect the VTVM common lead to the circuit ground.

(    )         Connect the VTVM probe to the positive lead of electrolytic capacitor C5 (200 mf) [top left edge].

(    )         Meter indication should read 10 kW or more.

(    )         Connect the VTVM probe to point GG (red wire) on circuit board.

               [Between switches SW4 & SW8, bottom center, positive end of diodes D1 & D2]

(    )         Meter indication should read 100 kW or more.

(    )         Connect the VTVM common lead to the G (black) banana jack [read panel.

(    )         Connect the VTVM probe to the negative lead of electrolytic capacitor C8 (200 mf) [second on left – top].

(    )         Meter indication should read 10 kW or more.

(    )         Disconnect the VTVM leads from circuit board.

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INITIAL INSTRUMENT SET-UPS

Oscilloscope Set-up

(    )         Set the Horizontal Sweep Rate switch to the .5 volts/div position.

(    )         Set the Vertical Sensitivity to the 1 volts/div position.

(    )         Set both the horizontal and vertical inputs to DC coupled.

Curve Tracer Set-up

(    )         Set the SWEEP VOLTAGE switch (SW1) to the OFF position.

(    )         Set the HORIZONTAL SENSITIVITY switch (SW6) to the 1 position.

(    )         Set the VERTICAL SENSITIVITY switch (SW7) to the 10 position.

(    )         Set the POLARITY switch (SW3) to the NPN position.

(    )         Set the SWEEP RANGE switch (SW2) to the 0 – 40 V position.

(    )         Set the STEP SELECTOR switch (SW9) to the CURRENT position.

(     )        Adjust the STEPS / FAMILY control (R47) to maximum counter-clockwise.

(    )         Set the STEP RANGE switch (SW8) to the 1 position.

(    )         Set the LIMITING RESISTOR switch (SW4) to the 100 position.

(    )         Set the LEFT - RIGHT switch [center top panel] to the LEFT position.

(    )         Set the LOOP control (R5) [rear panel] to center of rotation.

(    )         Set the NORM - CAL switch (SW10) [rear panel] to the CAL position.

(    )         Connect the three Curve Tracer outputs (H G V) [rear panel] to the oscilloscope inputs.

♦ A pair of BNC jacks can replace the H and V banana jacks on the rear panel to allow the use of standard coax cable connections.

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OSCILLOSCPOE CALIBRATION

(    )         Connect the Curve Tracer to the AC line voltage.

(    )         Adjust the SWEEP VOLTAGE control until switch just clicks on.

(    )         Adjust the STEPS / FAMILY control until four to six dots appear diagonally on the oscilloscope screen (see Figure 1.6).

(    )         Adjust the Horizontal and Vertical oscilloscope controls if the dots are too widely spaced.

(    )₁        Adjust the oscilloscope’s trace positioning controls to place the first dot on the line in the lower left-hand corner of the graticule.

(    )₂        Adjust the horizontal sensitivity until each dot appears on every other horizontal graticule.

(    )₃        Adjust the vertical sensitivity until each dot appears on the next higher vertical graticule.

(    )         Repeat the above three marked steps* until the oscilloscope display resembles Figure 1-6.

· The oscilloscope is now calibrated. DO NOT readjust the oscilloscope’s vertical and horizontal sensitivity CONTROLs.

(    )         Set the NORM-CAL switch [back panel] to the NORM position.

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OFFSET ADJUSTMENT

(    )         Adjust the OFFSET ADJ control (R84) [center of the circuit board] to maximum counter-clockwise.

(    )         Install the NPN transistor in the left transistor socket.

(    )         Adjust the STEPS / FAMILY control to maximum counter-clockwise.

(    )         Set the STEP RANGE switch to the .05 position.

(    )         Adjust the SWEEP VOLTAGE control until a trace appears across the bottom of the oscilloscope display (see Figure 1-9).

(    )         Set the VERTICAL SENSITIVITY switch until the trace is near the top of the display (see Figure 1-10).

(    )         Adjust the OFFSET ADJ control [on the circuit board] until the base line trace just becomes straight and flat (see Figure 1-11).

(    )         Set the VERTICAL SENSITIVITY switch to the .5 position.

(    )         Adjust the OFFSET ADJ control [on the circuit board] until the base line trace just becomes straight and flat (see Figure 1-11).

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TRANSISTOR TESTS

(    )         Adjust the SWEEP VOLTAGE control to the OFF position.

(    )         Set the HORIZONTAL SENSITIVITY switch to the 1 position.

(    )         Set the VERTICAL SENSITIVITY switch to the 5 position.

(    )         Set the POLARITY switch to the NPN position.

(    )         Set the SWEEP RANGE switch to the 0 – 40 V position.

(    )         Set the STEP SELECTOR switch to the CURRENT position.

(     )        Adjust the STEPS / FAMILY control to maximum counter-clockwise.

(    )         Set the STEP RANGE switch to the .01 position.

(    )         Set the LIMITING RESISTOR switch to the 100 position.

(    )         Set the LEFT - RIGHT switch [top panel] to the LEFT position.

(    )         Set the NORM - CAL switch [rear panel] to the NORM position.

(    )         Adjust the SWEEP VOLTAGE control until switch just clicks on.

(    )         Adjust the oscilloscope trace positioning CONTROLs to place the first dot on the line in the lower left-hand corner of the graticule (see Figure 1-12).

(    )         Adjust the SWEEP VOLTAGE control until a trace appears across the bottom of the oscilloscope display.

(    )         Adjust the STEPS / FAMILY control to maximum clockwise.

               (A set of nine curves plus the base line trace should appear.)

(    )         If some of the curves are off the screen –

               Set the VERTICAL SENSITIVITY switch to the 10 position.

(    )         If some of the curves appear crowded at the bottom of the screen –

               Set the VERTICAL SENSITIVITY switch to the 2 position.

(    )         Adjust slowly the STEPS / FAMILY control counter-clockwise until only the base line trace is left.

(    )         Adjust the STEPS / FAMILY control clockwise until three steps and the base line trace appears (see FIGURE 1-13).

(    )         If the display does not fill the screen –

               Set the VERTICAL SENSITIVITY switch one step counter-clockwise.

(    )         Set the LIMITING RESISTOR switch to the 50 position.

               (The upper curves increased slightly horizontally.)

(    )         Set the LIMITING RESISTOR switch to the 500 position.

               (The upper curves shorten or disappear horizontally.)

(    )         Set the LIMITING RESISTOR switch to the 100 position.

(    )         Set the HORIZONTAL SENSITIVITY switch to the 2 position.

               (The curves have shortened by a factor of two.)

(    )         Set the HORIZONTAL SENSITIVITY switch to the .5 position.

               (The curves have lengthened by a factor of two.)

(    )         Set the HORIZONTAL SENSITIVITY switch to the 1 position.

(    )         Set the VERTICAL SENSITIVITY switch to the .5 position.

               (One or two curves may go off the display.)

(    )         Adjust the LOOP control [rear panel] until the curves have a minimum of looping (see Figure 1-14).

(    )         Set the VERTICAL SENSITIVITY switch to the .5 position.

(    )         Set the STEP RANGE switch to the .02 position

               (The steps have doubled in value - some may go off the display.)

(    )         Set the STEP RANGE switch to the .005 position

               (The steps are half their original value.)

(    )         Set the STEP RANGE switch to the .01 position

(    )         Adjust the SWEEP VOLTAGE CONTROL to the OFF position.

♦ WARNING:     High voltages can be available at the C (collector) output terminals.

(    )         Set the SWEEP RANGE switch to the 0–200 V position.

♦ CAUTION:     Do not adjust the SWEEP VOLTAGE control any higher than necessary.

                             (*The MPSA20 NPN transistor is only rated at 40 volts maximum.)

(    )         Adjust the SWEEP VOLTAGE control carefully until the same traces seen before return.

               (These curves have a less polished appearance.)

(    )         Adjust the SWEEP VOLTAGE control counter-clockwise to the minimum voltage position.

· NOTICE:     Do not set the SWEEP RANGE switch to the 0–200 position unless voltages greater than 40 volts are required. The 40 V range provides cleaner and more precise displays.

(    )         Set the SWEEP RANGE switch to the 0–40 V position.

(    )         Position the dot in the upper right-hand corner of the graticule (see Figure 1-15).

(    )         Set the LIMITING RESISTOR switch to the 1000 position.

(    )         Set the HORIZONTAL SENSITIVITY switch to the 2 position.

(    )         Set the POLARITY switch to the PNP position.

(    )         Adjust the STEPS / FAMILY control to maximum counter-clockwise.

(    )         Adjust the SWEEP VOLTAGE control until the reverse breakdown of the C to E junction trace appears (see Figure 1-15).

(    )         Adjust the SWEEP VOLTAGE control to the OFF position.

(    )         Remove the NPN transistor from the left transistor socket.

(    )         Adjust all front panel controls only to their maximum counter-clockwise positions.

(    )         Calibration procedure is complete.