Heathkit Model IB-5281

RCL Bridge

Calibration Procedure

· If using the unit as a portable instrument, install a fresh set of 9-volt batteries and set the SOURCE switch (on rear of unit) to the BATT position.

· If powered using the IPA-5280-1 AC Power Supply, set the SOURCE switch (on rear of unit) to the LINE position.

· Disconnect all external components from the front panel terminals.

Ancillary Equipment Needed

VTVM

100 W 1% resistor

· Mount the 1% resistor on a dual banana plug to use as a calibration standard.

* * * * * * *

BIAS ADJUSTMENT

Refer to Pictorial 4-3

Illustration Booklet, page 5

(    )         Set the POWER switch to the OFF position.

(    )         Set the BIAS ADJ A control R9 to center of rotation.

               [Right front control on circuit board]

(    )         Set the FEEDBACK ADJ control R14 to center of rotation.

               [Right rear control on circuit board]

(    )         Set the BIAS ADJ B control R33 to center of rotation.

               [Center front control on circuit board]

(    )         Set the POWER switch to the ON position.

(    )         Connect the common (ground) lead of the VTVM to the chassis.

(    )         Set the VTVM FUNCTION switch to the DC+ position. 

(    )*       Set the VTVM RANGE switch to the 1.5V position.

(    )*       Touch the VTVM probe to test point A on the circuit board.

               [Near the right front corner of the transformer]

(    )*       Adjust the BIAS ADJ A control for a zero to +/- 0.1 volt meter indication.

· Adjust the BIAS ADJ A control slowly and wait for the meter indications to stabilize.

(    )*       Set the VTVM RANGE switch to the 5V position.

(    )*       Touch the VTVM probe to point A on circuit board.

(    )*       Adjust the BIAS ADJ B control for a 3.0 volt meter indication.

(    )*       Touch the probe to the collector of transistor Q8 [front lead].

               [Left of resistor R33 (18K W), front center of the circuit board]

(    )*       Adjust the BIAS ADJ B control for a 4.5 volt meter indication.

(    )         Repeat the above eight steps* until no change in the meter indications.

(    )         Set the POWER switch to the OFF position.

(    )         Disconnect the VTVM from the circuit board.

* * * * * * *

DIAL CALIBRATION

Refer to Pictorial 4-4

Manual, page 32

(    )         Set the BALANCE control R26 to maximum counter-clockwise.

(    )         Set the RANGE switch to the Rx1 position.

(    )         Set the LEVEL control to maximum counter-clockwise.

(    )         Connect a 100 W 1% resistor to the Z_x terminals.

(    )         Set the POWER switch to the ON position.

(    )         Adjust the LEVEL control until the meter reads 10 (full scale).

(    )         Adjust the BALANCE control until the meter reaches a null (lowest indication).

(    )         Set the LEVEL control to maximum clockwise.

(    )*       Adjust the BALANCE control to obtain the best null indication.

(    )*       Loosen the BALANCE control knob set screw without disturbing the null setting.

(    )*       Position the BALANCE pointer so it points to the 100 position on the outer scale.

(    )*       Tighten the BALANCE control knob set screw without disturbing the null setting.

(    )         Repeat the above four steps* until the best null indication matches the 100 scale position.

(    )         Set the POWER switch to the OFF position.

(    )         Disconnect the resistor from the terminals.

(    )         Calibration procedure is complete.