POWER SOURCES

BOLOMETER POWER SUPPLY

CIRCUIT DISCRIPTION

The circuitry provides power to the bolometer. It drives its DC voltage from the transformer T1 and the diode bridge D7. The smoothing of the supply is done by the capacitor C13. Varistor RV2 provides transient protection. The circuitry consists of U4 a switched mode power supply integrated circuit. It is configured in the step down mode of control. L2 is charged when the internal transistor is turned on. During the off cycle diode D4 is conducting and the energy stored in L1 is transferred into the capacitor C8, C8 maintains the average output voltage. Resistor R7 and R9 provides the feedback voltage to control the on/off duty cycle.

TESTING

• I did visual inspection by checking transformer T1 connection for correctness. The primary winding is on the left of the connector T1 as shown by the two wires on the photograph above. The secondary winding is on the right of T1 as shown by the two wires on the connector.
• I checked the orientation of the bridge rectifier with reference to diode D7 and D10.
• I connected 220VAC to DIN connector U5 on positive and negative input.
• I measured on terminal T1 for input which is expected to be 220VAC.
• I measured on terminal T1 for output which is expected to be ±30VAC.
• I measured for DC+ and DC- on the connector of the rectifier.
•  I checked on Din connector U5 for positive and negative voltage for wheel transducer supply.
• I measured on Din connector U5 for positive and negative voltage for bolometer power supply.

FAULT REPAIR

NB: The schematic diagram is attached at the back of this page

• This circuitry consists of wheel transducer power supply, flap power supply and bolometer power supply. The schematic diagram above shows the over view of the bolometer power supply. I have experienced faults when measuring for the DC output of the bolometer power supply on the DIN connector U5.
• I have used a meter to check components values.
• I have also used the meter to trace if there are any broken tracks by buzzing with reference to the schematic diagram.
•  I have found out that most of the time failure to get the expected output is because of capacitor C5 and C6 disfunctional or damage and also the regulator fails to deliver the required output.
• To fix this problem I had to replace the capacitors or regulators with the new ones.

 SAM7-200

CIRCUIT DISCRIPTION

The supply of 12VDC is applied to the circuit by a switch mode regulator B9.  The main voltage applied to the power supply must not be more that 18V and not less than 9V.  The voltage output of the switch mode power supply is 5VDC.  This is applied to the voltage regulator and the voltage output thereafter is 3.3VDC.  The 3.3VDC supplies the rest of the circuitry.

FAULT REAPIR

NB: The schematic diagram is attached at the back of this page

• I had some power failure during the test of this card as mentioned in the circuit diagram topic this card is made up of various sections designed for specific purposes as shown by the letters. The letter L donated the SMPSU which is of course responsible for the supply of power in the circuit.
• I have used the schematic diagram to identify the whole section of the SMPSU and do visual inspection to check the polarity of components.
• I have used the meter to test if the is any input voltage to the circuit and also if the voltage get regulated.
• The problem that I encountered was the polarity of the tranzorb TZ8 and D26 being soldered in wrong polarized way and also wrong regulator used.
•  During the test of this card I was advised to always measure the output voltage first to avoid damage to the other components. 
•  I had to replace this components using hot air station.

JEUMONT POWER SUPPLY

 

I have managed to wire and assemble this power supply using the basic hand skills that I have acquired during the first two month of my training. However I have used the schematic diagram as shown aside and the sample of this power supply as my reference when assembling and wiring.