Heathkit Model IP-27

Low Voltage Power Supply

Calibration Procedure

· With the power supply off, the meter pointer should be over the zero indication on the meter face.  If it is not, adjust the mechanical zero-adjust screw at the bottom of the meter until the pointer is properly aligned.

Ancillary Equipment Required

10 ohm 25 watts resistor (optional)

Differential voltmeter (optional)

* * * * * * *

NOTES

· Remove all jumper wires between the circuit grounds and chassis ground.

· Remove all loads from the supply terminals.

* * * * * * *

Front Panel Initial Conditions

(    )         Set the COARSE VOLTAGE switch to the AC OFF position.

(    )         Set the D.C. ON – RESET STANDBY switch to the RESET STANDBY position.

(    )         Set the COARSE CURRENT switch to 1.5 A.

(    )         Set the FINE VOLTAGE control to center of rotation.

(    )         Set the FINE CURRENT control maximum clockwise.

(    )         Set the CURRENT – VOLTAGE switch to the VOLTAGE position.

*Back Panel* Initial Conditions

(    )         Set the *ZENER CURRENT* control maximum counter-clockwise.

(    )         Set the *VOLTAGE CALIBRATE* control to center of rotation.

(    )         Set the *DC REGULATION* control to 1/8 turns from full clockwise.

(    )         Set the *METER* switch to the ZENER CURRENT position.

(    )         Set the POWER switch to the ON position.

(    )         Set the COARSE VOLTAGE switch to the .5 – 5 V position.

· When the *METER* switch is in the ZENER CURRENT position, the front panel meter will read a 5 ma (full scale) indication.

(    )         Adjust the *ZENER CURRENT* control for a meter reading of approximately 4 ma.

(    )         Set the *METER* switch to the NORMAL position.

(    )         Set the DC ON / RESET-STANDBY switch to the DC ON position.

(    )         Adjust the FINE VOLTAGE control and observe a meter swing from almost zero to full scale.

(    )         Set the FINE VOLTAGE control maximum clockwise.

(    )         Set the COARSE VOLTAGE switch to the 45 – 50 V position.

(    )         Adjust the FINE VOLTAGE control for a full scale meter reading.

(    )*       Set the *METER* switch to the ZENER CURRENT position.

(    )*       Adjust the *ZENER CURRENT* control for a full scale meter reading.

· The ZENER CURRENT readings are not critical and may vary.

(    )*       Set the *METER* switch to the NORMAL position.

(    )*       Adjust the *VOLTAGE CALIBRATE* control for a full scale meter reading.

· Because the *ZENER CURRENT* and the *VOLTAGE CALIBRATE* controls interact with each other, it will be necessary to repeat the above four steps* until no meter changes are observed.

(    )         Set the *METER* switch to the NORMAL position.

(    )         Set the COARSE VOLTAGE switch to the AC OFF position.

DC REGULATION CONTROL ADJUSTMENT

(optional)

· If a differential voltmeter is not available, leave the DC REGULATION control as originally set and proceed to the FINAL ADJUSTMENTS section.

Front Panel Initial Conditions

(    )         Set the CURRENT – VOLTAGE switch to the VOLTAGE position.

(    )         Set the COARSE VOLTAGE switch to the 10 – 15 V position.

(    )         Set the FINE VOLTAGE control maximum clockwise.

(    )         Set the COARSE CURRENT switch to the 1.5a position.

(    )         Set the FINE CURRENT control maximum clockwise.

(    )         Set the D.C. ON – RESET STANDBY switch to the RESET STANDBY position.

(    )         Connect a differential voltmeter to the output terminals

(    )         Set the D.C. ON – RESET STANDBY switch to the D.C. ON position.

(    )*       Note the unloaded output voltage on the differential voltmeter.

(    )*       Set the D.C. ON – RESET STANDBY switch to the RESET STANDBY position.

(    )*       Connect a 10 ohm 25 watts resistor to the output terminals.

(    )*       Set the D.C. ON – RESET STANDBY switch to the D.C. ON position.

(    )*       Note the loaded output voltage on the differential voltmeter.

(    )*       Adjust the *DC REGULATION* control to match the meter readings.

(    )*       Set the D.C. ON – RESET STANDBY switch to the RESET STANDBY position.

(    )*       Disconnect the 10 ohm resistor from the output terminals.

· In order for the output voltage regulation to be the same both loaded and non-loaded, it will be necessary to repeat the above eight steps* until no meter changes are observed.

FINAL ADJUSTMENTS

 (    )        Set the FINE VOLTAGE control maximum counter-clockwise.

(    )         Set the COARSE VOLTAGE switch to AC OFF.

(    )         Set the D.C. ON – RESET STANDBY switch to the RESET STANDBY position.

(    )         Set the POWER switch to the OFF position.

(    )         Disconnect the resistive load.

(    )         Calibration procedure is complete.