Laboratory Equipment Maintenance, Diode and BJT Testing, Soldering Basics

This presentation is related to the vocational skill course offered by university of Mumbai for the first year undergraduate students. The basic of laboratory equipment, soldering technique are discussed. Testing of the diodes and bipolar junction transistor is an important part of the physics laboratory practical.

1. FYBSC Physics (Vocational Skill Course ) Course code: USPHPVSC1 Title: - Laboratory Equipment Maintenance Asst. Prof. Dr. Vikas V. Deshmane

2. DIODE

3. DIODE

4. DIODE

5. DIODE

6. DIODE

7. DIODE

8. DIODE

9. DIODE

10. DIODE

11. DIODE

12. DIODE

13. DIODE

14. TRANSISTOR

15. TRANSISTOR CONSTRUCTION

16. TRANSISTOR BIASING

17. TRANSISTOR TYPES

18. TRANSISTOR TERMINALS

19. TESTING A TRANSISTOR Remove the transistor from the circuit for accurate test results. Step 1: (Base to Emitter) Hook the positive lead from the multimeter to the to the BASE (B) of the transistor. Hook the negative meter lead to the EMITTER (E) of the transistor. For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see “OL” (Over Limit). Step 2: (Emitter to Base) Hook the positive lead from the multimeter to the to the EMITTER (E) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor. For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V .

20. TESTING A T RANSISTOR Step 3: (Base to Collector) Keep  the positive lead on the BASE (B) and place the negative lead to the COLLECTOR (C). For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see "OL" (Over Limit ). Step 4: (Collector to Base) Hook the positive lead from the multimeter to the to the COLLECTOR (C) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor. For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V . Step 5: (Collector to Emitter) Hook the positive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E) – A good NPN or PNP transistor will read "OL"/Over Limit on the meter. Swap the leads (Positive to Emitter and Negative to Collector) – Once again, a good NPN or PNP transistor should read “OL”. If your bipolar transistor measures contrary to these steps, consider it to be bad. You may also be able to use the voltage drop to determine which lead is the emitter on an unmarked transistor, as the emitter-base junction typically has a slightly higher voltage drop than the collector-base junction.

21. CAUSES OF TRANSISTOR FAILURE  F aults could be due to Improper Packaging, Inadequate Mechanical Stress, False Circuitry, Wire-related Problems, Thermal Shocks, Contamination, Or Damaged Parts. Manufacturing Faults These faults reduce the performance capabilities of a transistor and lead to failures during the operation .

22. Basics of Soldering : Soldering alloy, Soldering Iron Soldering Components: Soldering Iron Solder Solder Braid (Flux) Printed Circuit Board Wire Strippers

23. Soldering Alloy: Solder alloys are typically made of lead ( Pb ) and tin (Sn ) A common composition is 60% tin and 40% lead, which melts at 188°C.  Solder has a low melting point, which is lower than the melting points of its constituent metals. This makes it ideal for soldering and welding electrical wires.  This alloy is easy to work with and forms strong connections with other metals. Soldering Iron Soldering is a process that uses a soldering iron to melt solder and fill the joint between two or more items.  The solder has a lower melting point than the other metals. The iron is heated to temperatures above its melting point, which is around 600°F . A soldering iron is made up of several parts.   Tip: The tip of a soldering iron is made of a copper core that's plated with other metals, such as iron, for durability. Copper is used because it conducts heat well and has an affinity for solder, which helps the solder melt and stick to the tip.  Heating element: The heating element brings the tip of the soldering iron up to the temperature needed for soldering.  Handle: The handle is insulated to allow the user to hold the soldering iron safely.  Plug: The soldering iron can be plugged into a wall outlet or a soldering station.  Basics of Soldering: Soldering alloy, Soldering Iron

24. Soldering Procedure Step # 1. Pre-Cleaning: The work surfaces to be soldered must be free of all grease, oil, dirt, oxide, etc. because a solder will not wet a dirty or oxide covered surface. Mechanical cleaning is usually done by the use of wire-brushing, filing, machining, sanding or by employing steel wool or emery cloth . For chemical cleaning trichloroethylene and hot alkali detergents are widely used. Step # 2. Fitting or Mounting: It is very important that the cleaned parts are fitted closely together in the desired design configuration to achieve the optimal strength . Step # 3. Preparation & Application of Flux : Flux for bar or solid type solders is applied to joint as a paste. A flux of lower melting point can be made by combining 1 part sal am­moniac (NH 4 Cl) with 3 parts of zinc chloride. Such a flux melts at 180°C and is corrosive in nature. Flux may also be contained in the solder. It prevents dust or moisture and will not corrode delicate wiring.

25. Soldering Procedure Step 4 . Heating the Parts: The proper application of heat is of utmost importance in any solder­ing operation. The heat should be applied in such a way that the solder melts while the surfaces are heated to permit the molten solder to wet and flow over the surfaces. Step 5 . Applying the Solder: The workpieces must be held firmly together to prevent a relative movement between them during the soldering operation. If flux-cored solder is used it would be applied directly to the joint and not to the soldering tip. When the joint is hot enough the molten solder will flow into it by capillary action. Step 6 . Cooling the Soldered Joint: Once the desired amount of solder has been applied, the heat source is removed and the joint is allowed to cool to the room temperature undisturbed on its own. Step # 7. Post Cleaning: The corrosive flux residue is removed by the final op­eration of post cleaning. The removal of flux residue is especially important where joints must be subjected to humid environment. Residues of zinc chloride fluxes are moisture absorbent and must be removed through washing in hot water.

26. Steps of De-soldering 1. Unwind a few inches of braid from the coil. 2. If your solder wick does not have flux on it, it would be a good idea to add flux to the section you are going to use to make for a clean removal. 3. Place the braid over the joint you want to rework. 4. Place a hot soldering iron against the braid and desired pin. 5. Wait a few seconds. The solder will flow off the pin and onto the braid. 6. Remove the braid. The braid will be very hot at this point, so make sure not to touch the braid itself, only the spool. 7. Remove the component. 8. Repeat steps 1-5 to remove excess solder .

27. Soldering : Good or Bad The good joint is recognized by a shiny surface, the solder curving smoothly into the copper surfaces as the solder wets the surface with only just enough applied to enable the outline of the copper cable to be clearly seen.

28. Dry Soldering A dry solder joint is a weld soldered using an insufficient quantity of solder. A dry solder joint is a soldering defect that occurs when the solder does not properly wet or adhere to the component leads and PCB pads. It can lead to an unreliable joint or an open circuit. Factors such as insufficient heat, oxidized surfaces, improper soldering, or using low-quality solder cause dry joints . As a result, the electronic circuit might experience high resistance, noise, or intermittent conductivity .