Fault Finding in Electronic Circuit board
The best way to avoid problems in electronic circuit assembly is to be always alert while working, to think about what you are doing and to try always to be neat. If, despite your best efforts, the circuit does not work as it should when tested, then follow a logical test procedure which will usually find the faults in the shortest possible time. First carry out a series of visual tests:
1 Is the battery or supply correctly connected?
2 Is the battery flat or the supply switched off?
3 Is the circuit constructed exactly as it should be according to the circuit diagram?
4 Are all the components in place?
5 Check the values of all the components.
6 Are all the components such as diodes, capacitors, transistors and ICs connected the correct way round?
7 Have all connections and links been made?
8 Have all the necessary breaks been made in the stripboard?
9 Are all the soldered joints good?
10 Are any of the components hot or burnt? If the fault has not been identified by the first ten tests, ask someone else to carry them out. You may have missed something which will be obvious to a fresh pair of eyes. If the visual tests have failed to identify the fault, then further meter tests are called for as follows:
11 Check the input voltage and the output voltage. Check the mid-point voltage between components which are connected in series with the supply.
12 Variable resistors may suffer from mechanical wear. Check the voltage at the wiper as well as across the potentiometer.
13 Check the coil voltage on relays; if this is low, the coil contacts may not be making.
14 Is the diode connected correctly? Short circuit the diode momentarily with a wire link to see if the circuit works. If it does the diode is open-circuit.
15 Check capacitor–resistor circuits by momentarily shorting out the capacitor and then observing the charging voltage. If it does not charge, the resistor may be open-circuit. If it charges instantly, the resistor may be short-circuit. Check the polarity of electrolytic capacitors. Check the capacitor leads for breaks where the lead enters the capacitor body.
16 Check the base–emitter voltage of the transistor. A satisfactory reading would be between 0.6 and 1.0V. Temporarily connect a 1k resistor between the positive supply and the base connection. If the transistor works, the base feed is faulty. If it does not work, the transistor is faulty. 17 Short out the anode and cathode of the thyristor. If the load operates, the thyristor or the gate pulse is faulty. If the load does not operate, the load is faulty.