TTI EX752M Service Manual page 10

Refer to the General section for dismantling instructions and safety precautions. Component
adjustment references are given as Channel A/ Channel B, e.g. VR5/VR105; Channel A is the
left-hand output. All adjustments are on the front panel control board unless otherwise stated.
Allow 5 minute warm-up before commencing calibration.
Equipment Required
A 5½ digit multimeter with better than 0.05% accuracy on dc volts and better than 0.1% accuracy
on dc current (to 4A); alternatively use a precision shunt for current measurement.
Rheostat or other high power load arrangement to provide up to 4A load at 75V.
Mode A (75V/2A x 2)
Adjust Channel A and Channel B independently as follows.
Voltage Calibration
Connect the DMM (set to Volts) across the output. Set voltage and current controls to minimum.
Switch output ON (Check LED is on) and check for a reading of 00.0V ± 0.1V on the Volts display
and DMM; check the Amps display reads 0.00 ± 0.01A.
Set voltage and current controls to maximum. Adjust VR5/VR105 (maximum output volts) for a
reading of 75.35V to 75.45V on the DMM. Adjust VR6/VR106 (measured output volts) until the
Volts display matches the reading on the external DMM.
Switch output OFF. Adjust VR10/110 (preset volts) until the Volts display shows 75.4.
Current Calibration
Switch output OFF. Set output voltage to nominally 2V. Set current control to minimum. Connect
the DMM (set to Amps) and load in series across the output. Switch output ON.
Adjust VR8/108 (offset compensation of current control error amp) for a reading of 0.003A
± .001A on the DMM. Check that the CC LED is ON.
Increase voltage controls and current control to maximum. Adjust load until the DMM reads 2.00A
± 0.02A. Adjust VR7/107 (measured output current) until the Amps display matches the DMM
reading.
Reduce load until the CC LED is ON. Adjust VR4/104 (maximum output current) until the Amps
display shows 2.05.
Control pcb calibration points (viewed from rear)
Calibration
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