______________________________________________
HARRIS
888-9058-001
WARNING: Disconnect and lockout AC primary power prior to servicing
193
inlet temperature, it should be below the maximum temperature rating of 50
o
C. If the
temperature is more than a few degrees above outside temperature, the air supply
system may not be adequate.
If an improper module fault is suspected, allow the module to cool to room ambient.
Re-enable the module, a real temperature fault will not cause an immediate fault, the
thermal mass of the heat sink requires at least ten minuets to generate a temperature
fault.
Check quarter module temperature calibration as follows: 50 Volts to the
module and, without enabling it, check the voltages at test point TP-1 on each quarter
module center board. This voltage represents the temperature of the heatsink at the
location of the temperature sensor. The voltage is calibrated to be
5.30
Volts at a
temperature of 25
o
C. The calibration control is R2 on each quarter module board. The
voltage at TP1 is compared against a reference voltage of 5.82 Volts generated by a
voltage divider.
Measure the quarter module temperature reporting inputs at U13 pins 5,7,9, and 11. If
any quarter module input is lower than the reference check for an overheated quarter
module, an incomplete temperature reporting circuit, or failure of a quarter module bias
and temperature reporting circuit. If the reference voltage is lower than all the
temperature reporting lines, the outputs of U13 should be high, and the output of U5
should be low, and the module should not be reporting a temperature fault. If a
temperature fault is reported check for proper operation of comparator U13, Schmitt
trigger U5, or possible PAL failure.
Pass FET Failure Fault (6 blinks)
Should one of the pass FET DC switch transistors
fail to a shorted condition, the control board will sense it and blink the red LED six
times. The pass FETs are 60 amp 100 Volt MOSFETs used as DC switches to enable
and disable the module as necessary by applying or removing DC from the quarter
modules.
!
CAUTION:
IF A PASS-FET FAILURE IS INDICATED, THE MODULE CANNOT BE TURNED
OFF EXCEPT BY TURNING OFF THE PA CABINET OR BY DISABLING THE
POWER SUPPLY WHICH POWERS THE PA. A MODULE INDICATING PASSFET
FAILURE SHOULD NOT BE REMOVED FOR SERVICE WITH POWER
APPLIED, AS COMPONENT DAMAGE COULD RESULT.
A shorted pass FET (drain-source short) is normally confirmed by measuring the
resistance from the red 50 Volt wire of any quarter module to the +50 Volt pins of the
input connector with an ohmmeter.
