MEASURE INSTRUMENTS


OSCILLOSCOPE


 HOT BOX ADC MICRO CARD
  • I have used this oscilloscope during repair to display the frequency of the hot box ADC micro board. The test was carried to check the output frequencies of various ICs which include microprocessor oscillator, real time clock oscillator, discrete oscillator and analogue to digital converter oscillator. The expected outputs signal of each IC differs with reference to the type of IC used, however this will be discussed more in the section of circuit diagrams.
  • I have also used this instrument to check the duty cycle and amplitude of the discrete oscillator.
  • I measured the analogue to digital converter voltage with the oscilloscope and also the multimeter for accuracy measures.
  • BOLOMETER SENSOR
  • This oscilloscope was used to test and display the output Vrms signal of the bolometer sensor when repairing.
  •  The output Vrms of the bolometer is expected to first rise from 9V to 24V and later drop down to stabilize at 16V to 17V.
  • If the output Vrms displayed by the oscilloscope does not meet this condition therefore I had to fault find and repair.
LOGIC PROBE
  • I have used this instrument to trace fault of MAX232 IC on SAM7-200 PC Board with the help of schematic diagram and sample Board as my reference. The logic probe indicated status change in the output signal when the card was powered, before and after test.
  • I was dealing with surface mount device so I had to check if the supply rail is 3.3 volts or less. The logic probe does not allow to work with this voltage because is not enough to reach logic levels.
  •  It was difficult to probe since I was working on surface mount as there is real danger of shorting pins.
  • The task of checking the output signal on MAX232 was carried in the order below
  1. I connected the black clip to ground or to a common point of the PC board
  2. I connected the red clip to the positive supply of the circuit.
  3. I had to select the logic family between CMOS or TTL in my case I was using TTL.
  4. I used the probe to connect to the output pin of MAX232 and monitor the signal. The red LED displayed high, green LED displayed low and yellow LED simply tells if a pulse is detected
  5.  In some conditions I was not sure if a pulse is detected or not so I had to set MEM on the probe which allowed the probe to capture if there are short pulses.
MULTIMETER
  • The multimeter was used to check components functionality, values and polarity when I was repairing FSU, bolometer sensors, bolometer power supply, DC snubbing units and Hot Box ADC micro cards.
  • I have also used the multimeter to measure the values of each component to confirm is the value written is as required, this helps minimize chances of making unnecessary faults. These was done before populating on the PCBs for Digital input card (S2/DIP22), Digital output card (S2/DOP22), Scanner Extension Card (S2/SCE) and relay interface card.
  • To measure the value of the resistor I had to switch the meter to ohm.
  • To measure the capacitance I had to switch the meter to farad.
  • The multimeter also helped me to check and confirm output voltage of the dual power supply when I was testing relay interface cards.


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