68805-M
ARC LAMP POWER SUPPLY
14
VI. CALIBRATION AND TROUBLESHOOTING
Warning:
The power module (27-20-007) of the model 68805 power supply has no field serviceable
parts. Do not attempt to repair the module in the field. If a failure of the module occurs,
then contact your local representative for service.
Only qualified service personnel should attempt repair or calibration of the unit. They
must exercise extreme caution when working in the unit with power on. Dangerous
voltage levels exist within the unit which could harm if proper, electronic troubleshooting
techniques are not adhered to.
CALIBRATION
The required equipment to calibrate the power the power supply, is an external 300 watt load
resistor of less than 3
S
, and external voltage and current meters.
With the unit off, remove the top cover, and connect the ammeter in series with the load resistor.
Connect the voltmeter across the positive and negative output posts at the rear panel. Turn the
“ADJUST” knob full counter–clockwise.
Switch the power supply on and adjust the output via the front panel control so that the output
current, as viewed on the external ammeter, is an even value. Hold the meter select switch in the
“AMPS” position and trim R6 so that the front panel meter display agrees with the external
ammeter.
Release the meter select switch and without changing the control knob setting press the
“PREADJUST” switch. Be sure that you are reading this value on the current scale when doing
this calibration. Trim R16 so that the front panel meter displays the output current setting. There
will be a slight decrease in the output current when this switch is pressed. Therefore, adjust R16
to the output current value that was measured with the external ammeter prior to pressing this
switch.
Hold the meter select switch in the “VOLTS” position and, rotate the front panel control knob so
that the output voltage is an even value. Trim R13 so that the front panel meter agrees with the
external voltmeter.
Release the meter select switch and adjust the output with the front panel control until the product
of the external meters is an even value. Trim R12 so that the front panel meter agrees with this
value. Calibration is now complete. Switch the power supply off, and replace the cover.
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