Heathkit Model IM-1212

Digital Multimeter

[Nixie tube model]

Calibration Procedure

· Disconnect all external cables, components, and wires from the output terminals.

Ancillary Equipment Needed

Frequency Counter

* * * * * * *

(    )         Disconnect the line cord from the AC power lines.

(    )         Set the POWER switch to the OFF position.

* * * * * * *

CIRCUIT BOARD INITIAL ADJUSTMENTS

Refer to Figure 2-2

Construction Manual page 41

(    )         Adjust the AC CAL control to the center of rotation.

(    )         Adjust the 2M ADJ control to the center of rotation.

(    )         Adjust the 200K ADJ control to the center of rotation.

(    )         Adjust the 2000 ADJ control to the center of rotation.

(    )         Adjust the 200 ADJ control to the center of rotation.

(    )         Adjust the ZERO ADJ control to the center of rotation.

(    )         Adjust the OSC ADJ control to the center of rotation.

(    )         Adjust the AC TP ADJ control to the center of rotation.

(    )         Adjust the DC CAL control to maximum counter-clockwise, then a ¼ turn clockwise

* * * * * * *

FRONT INPUT INITIAL ADJUSTMENTS

Refer to Figure 2-1

Construction Manual page 39

(    )         Set the FUNCTION switch [SW1] to the OFF position.

(    )         Set the SCALE switch [SW2] to the 2 position.

(    )         Connect the line cord to the AC power lines.

(    )         Set the FUNCTION switch to the DCV position.

               (Allow the unit to warm up for 30 minutes)

· The two right-hand digits (displaying any number) and the decimal point to the left should all be lit. No other lamp should be lit.

* * * * * * *

ZERO ADJUSTMENT

Refer to Figure 2-2

Construction Manual page 41

(    )         Connect a test lead to the red V input jack.

(    )         Connect the same test lead to the black C input jack.

(    )         Adjust the ZERO ADJ control for a reading of .01.

(    )         Adjust the ZERO ADJ control until the reading just changes to .00.

· The display should change back and forth between .01 and .00.

(    )         Disconnect the test lead from both the red V and black C input jacks.

* * * * * * *

OSCILLATOR ADJUSTMENT

(Using a Frequency Counter)

(    )         Set the FUNCTION switch to the KW position.

(    )         Connect a test lead to the Frequency Counter’s common input.

(    )         Connect the same test lead to the Multimeter’s black C input jack.

(    )         Connect a test lead to the Frequency Counter’s “hot” input.

(    )         Connect the same test lead to either jumper A [see Pictorial 1-2, page 8] or to pin 14 of IC7 (SN7490) [see Pictorial 2-3, page 19].  

(    )         Adjust the OSC ADJ control for a frequency counter reading of 50 – 60 Hz.

               (Match to the known AC line voltage frequency.)

(    )         Disconnect both test leads from the Multimeter.

(    )         Proceed to the DC VOLTS CALIBRATION section.

* * * * * * *

OSCILLATOR ADJUSTMENT

(Without a Frequency Counter)

(    )         Set the FUNCTION switch to the KW position.

(    )         Adjust the OSC ADJ control for a reading of OVER .85, within an error of + .15 digits.

· If a reading of OVER .85 is unobtainable, adjust the OSC ADJ control for the nearest possible reading. Then leave the control set at that point.

* * * * * * *

DC VOLTS CALIBRATION

Refer to Figure 2-2

Construction Manual page 41

(    )         Connect a test lead to the red V input jack.

(    )         Connect the same test lead to the DC CAL TP test point [circuit board – left rear].

· Reference the calibration voltage recorded on the transformer’s insulator to perform the following steps.

· Observe that the calibration voltage number has four digits, whereas the Multimeter can display only three digits. Round the third digit up if the fourth digit is greater than 4.

· If the number is greater than 1.99, the first digit will not be displayed and the OVER lamp shall be lit.

(    )         Set the FUNCTION switch to the DCV position.

(    )         Adjust the DC CAL control until the reading matches the calibration voltage recorded on the transformer’s insulator.

(    )         Disconnect the test lead from both the test point and the red V input jack.

* * * * * * *

OSCILLATOR ADJUSTMENT

(Using a Frequency Counter)

(    )         Set the FUNCTION switch to the KW position.

(    )         Connect a test lead to the Frequency Counter’s common input.

(    )         Connect the same test lead to the Multimeter’s black C input jack.

(    )         Connect a test lead to the Frequency Counter’s “hot” input.

(    )         Connect the same test lead to either jumper A [see Pictorial 1-2, page 8] or to pin 14 of IC7 (SN7490) [see Pictorial 2-3, page 19].  

(    )         Adjust the OSC ADJ control for a frequency counter reading of 50 – 60 Hz.

               (Match to the known AC line voltage frequency.)

(    )         Disconnect both test leads from the Multimeter.

(    )         Proceed to the DC CAL Adjustment section.

* * * * * * *

OSCILLATOR ADJUSTMENT

 (Without a Frequency Counter)

(    )         Set the FUNCTION switch to the KW position.

(    )         Adjust the OSC ADJ control for a reading of OVER .85, within an error of +/- .15 digits.

· The reading should fall within .15 digits – no less than OVER .70 or no greater than OVER 1.00.

* * * * * * *

DC CAL ADJUSTMENT

(    )         Set the FUNCTION switch to the DCV position.

(    )         Connect a test lead to the red V input jack.

(    )         Connect the same test lead to the DC CAL TP test point.

(    )         Adjust the DC CAL control until the reading matches the calibration voltage recorded on the transformer’s insulator.

(    )         Disconnect the test lead from the test point.

* * * * * * *

ZERO ADJUSTMENT

Refer to Figure 2-2

Construction Manual page 41

(    )         Connect the same test lead to the black C input jack.

(    )         Adjust the ZERO ADJ control for a reading of .01.

(    )         Adjust the ZERO ADJ control until the reading just changes to .00.

· The reading should change back and forth between .01 and .00.

(    )         Disconnect the test lead from the black C input jack.

(    )         Repeat the entire DC VOLTS CALIBRATION section until the correct readings are obtained.

* * * * * * *

AC VOLTS CALIBRATION

Refer to Figure 2-2

Construction Manual page 41

(    )         Set the FUNCTION switch to the DCV position.

(    )         Set the SCALE switch to the 20 position.

(    )         Connect a test lead to the red V input jack.

(    )         Connect the same test lead to the AC CAL TP test point [circuit board – left rear, by transformer].

(    )         Adjust the AC TP ADJ control for a reading of 16.3.

· The reading may vary between 16.2 and 16.4.

(    )*       Disconnect the test lead from the test point.

(    )*       Set the FUNCTION switch to the ACV position.

(    )*       Connect the same test lead to the AC CAL TP test point, and allow the display to stabilize.

(    )*       Adjust the AC CAL control for a reading of OVER 0.0.

· The reading may vary between 19.9 and OVER 0.0.

· A proper adjustment will cause it to show a reading of OVER 0.0 most of the time.

(    )         Repeat the last four steps * until the correct readings are obtained.

(    )         Disconnect the test lead from both the test point and the red V input jack.

* * * * * * *

OHMS CALIBRATION

Refer to Figure 2-2

Construction Manual page 41

(    )         Set the FUNCTION switch to the KW (200W) position.

(    )         Connect a test lead to the fuseholder [F1] lug 2 [rear].

· The OHMS CAL TP test points are not labeled in Figure 2-2 [circuit board, lift side center].

· All the readings may vary between 19.9 and OVER.

(    )¹        Set the RANGE switch to the 200 W position.

(    )         Connect the same test lead to the 200 W resistor [test point 1 (front)].

(    )         Adjust the 200 ADJ control for a reading of OVER 00.

(    )         Disconnect the test lead from the test point.

(    )²        Set the RANGE switch to the 2 position.

(    )         Connect the same test lead to the 2 kW resistor [test point 2].

(    )         Adjust the 2000 ADJ control for a reading of OVER .00.

(    )         Disconnect the test lead from the test point.

(    )³        Set the RANGE switch to the 20 position.

(    )         Connect the same test lead to the 20 kW resistor [test point 3].

(    )         Adjust the 20K ADJ control for a reading of OVER 0.0.

(    )         Disconnect the test lead from the test point.

(    )⁴        Set the RANGE switch to the 200 position.

(    )         Connect the same test lead to the 200 kW resistor [test point 4].

(    )         Adjust the 200K ADJ control for a reading of OVER 00.

(    )         Disconnect the test lead from the test point.

(    )⁵        Set the RANGE switch to the 2K position.

(    )         Connect the same test lead to the 2 MW [test point 5].

(    )         Adjust the 2M ADJ control for a reading of OVER .00.

(    )         Disconnect the test lead from the test point.

(    )         Repeat the five ohms adjustments ^X above until stable readings are obtained.

(    )         Disconnect the test lead from the fuseholder [F1] lug 2.

(    )         Set the FUNCTION switch to the OFF position.

(    )         Disconnect the line cord from the AC power lines.

(    )         Calibration procedure is complete.