The Puzzle Boxes

Table of Contents

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1 Board fault finding and multimeter testing

  • Over the past year, you learned about electronics by making different projects that have been supplied to you. In this unit, you'll be equipped with diagnostic skills to further improve your ability to fix problems with circuits when they occur, to create and upload original programs to circuits and to create circuits without having to use the chemical etch tank.
  • If you want some additional help, try reading through this short guide to using a multimeter.

Identifying the Components

  • Firstly, lets identify the components and which way around the should go.
  • The 78L05 voltage regulator.

78L05_Front.JPG 78L05_Top.JPG

  • On the PCB.

78L05_PCB.JPG

  • The Diode.

Diode_pic.JPG

  • On the PCB.

Diode_PCB.JPG

  • The 8-Pin carrier.

8pin_Carrier.JPG

  • On the PCB.

8pin_PCB.JPG

  • The LEDs.

LED_flat_edge.JPG

  • On the PCB.

LED_PCB.JPG

  • Take you time to get familiar with these components before you start to identify them and fault find.

The Board Faults

  • There are 7 different circuit boards labelled A - G below with faults on them. There is also a component box with 3 different components to test and 4 different resistors to test, labelled A,B,C, 1, 2, 3 and 4. Inside the box are components, soldered to Machine screws (bolts with screwdriver heads). You will need to use the different settings on the multimeter as well as your ingenuity and knowledge of electronics to test the contents of each.
  • The PCB's have a number of faults on them, here is a list of the possible faults you will find:
    1. Voltage regulator is the wrong way around.
    2. There is a dry joint (the solder does not go all the way around the component).
    3. A track has been lifted off the board.
    4. The 8-pin Chip carrier is the wrong way around.
    5. There is a short circuit (components that are not supposed to be joined are connected).
    6. There is an LED the wrong way around.
    7. Diode is the wrong way around.
  • Open a .txt (NotePad) or .doc (Word) file and record which board has which fault.
  • Board A

Box_A.jpg

  • Board B

Box_B.jpg

  • Board C

Box_C.jpg

  • Board D

Box_D.jpg

  • Board E

Box_E.jpg

  • Board F

Box_F.jpg

  • Board G

Box_G.jpg

  • Now move onto the puzzle boxes below and record your findings in the same .txt file.

The Puzzle Boxes

  • Below is a video on how to use a multimeter. Please watch this before continuing testing below.
  • Box A: An LDR. LDRs typically have a resistance value from 400 to 2M (2 million) Ohms, depending on the amount they are exposed to: More light = less resistance.

    i. Select the 200k setting on the multimeter for Box A, B and C below. Read the resistance across the LDR, and write it down.

LightLDR.jpg ii. Put your finger over the LDR and read the resistance again. DarkLDR.jpg

  • Box B: The component in here is called a potentiometer. By turning the dial, the resistance between its 3 pins can be changed.

    i. What is the resistance between pins 1 and 3?

    ii. Turn the dial to face pin 2. What is the resistance between pins 1 and 2? What is the resistance between 2 and 3? What number do you get when these values are added together?

    iii. Turn the potentiometer wiper to the left and right notches marked near the dial and measure the resistance at each point.

  • Box C: The green component is called a thermistor(Thermal Resistor). Its resistance changes in response to temperature.

    i. To test the component, you can put your finger on it and this will raise the temperature slowly. If you keep the meter on it, you should see the resistance change.

    Resistors There are 4 resistors included in the box, use a multimeter to record the values of each resistor in the same text file you created.

Badge It

  • To complete the badges you will need to click on the link at the bottom and complete the quiz. This will automatically badge your work.
  • You will need to be logged into www.bournetolearn.com to complete the badge.
  • Click on this link for the board faults quiz.
  • Please ensure you also upload the .txt(Notepad) document you have completed as evidence of your work.

Below is how you will be awarded the badges.

  • Correctly complete 3 of the 'board fault' tasks and 1 of the 'puzzle box' tests.
  • Correctly complete 5 of the 'board fault' tasks and 2 of the 'puzzle box' tests.
  • Correctly complete all of the 'board fault' tasks and all of the 'puzzle box' tests.

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