Basic electronic parts knowledge
1 Under construction!!!
Sometimes it can be handy to know what the function of an electronic part is. If you just replace that transistor because someone says so you don't need to read this ;)
2 Resistor types and functions (includes NTC and varistor)
A resistor is a commonly used part in electronics and when you look at a pinball CPU board for instance you will see lots of them. They come in different shapes and sizes. In general the smaller sizes have colored bands around them that indicate the value while the bigger sizes have printed text. SMD (surface mount) resistors are the smallest though and they have a text on them so there's an exception.
What does it do? A resistor provides resistance to current flowing from a positive voltage to ground. It can be compared to a water tap, when the tap is closed the resistance for the water is so high that there want be any water flowing and when the tap is fully opened there's (almost) no resistance which causes a big flow of water. Of course you can also open the tap half-way giving resistance but still allowing water to flow. A resistor works the same, when you have a very high or even infinite resistance there won't be any current flow, when there's no resistance at all all the current will flow (short-circuit). Just like with the water tap you can adjust the current flow by adjusting the resistance.
Resistance is stated in Ohm's and the symbol is . 1.000 Ohm = 1kOhm (k for kilo) and 1.000.000 Ohm = 1MOhm (M for Mega). Resistance values are noted this way: 1.5 Ohm = 1R5, 1.5 kOhm = 1k5, 1.5MOhm = 1M5.
Some examples of standard "fixed value" resistors:
Special resistor types
NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient).
An NTC or PTC is a resistor that varies it's resistance according to it's temperature. In the case of an NTC the resistance lowers while the temperature rises, the opposite of an NTC is the PTC which has a resistance that rises when the temperature rises. NTC's are commonly used in pinbalsl machines as inrush current limiters. It is placed in series with the transformer (the load) and when the pinball is first turned on the NTC is still cold causing a resistance and limiting the current at that moment. Because of the current flowing through the resistor it will become warm (hot!) very fast which lowers it's resistance close to zero allowing more current to flow for the pinball's normal operation. A pinball that lacks the NTC will often cause the fuse in your home to trip when turning the pinball on, especially circuit-breakers are very sensitive to this!
VDR (Voltage Dependent Resistor, Varistor, MOV)
A varistor is a resistor with a resistance that depends on the voltage on the resistor. The most used type is the Metal Oxide Varistor (MOV).
The most important feature is the specified clamping voltage, when the applied voltage is below the clamping voltage it's resistance is very high and there won't be any current flow through it except for some leakage but when the applied voltage is above the clamping voltage it's resistance will be close to zero creating a shortcut. This feature is used on the AC input of pinballs to short the extremely high input voltage of a lightning strike for instance and thus preventing that voltage to go into the transformer and from there to all electronics. Sometimes it is also used in circuits where voltage peaks are present because of induction voltages from coils, when these voltage voltages aren't surpressed they can damage sensitive parts like MOSFETs. As said the clamping voltage must be above the normal line voltage. For US line voltage (120V AC) a 130V MOV is used, for the European line voltage (240V AC) a 275V MOV is used.
Some varistor examples:
3 Capacitor types and functions
Some examples of capacitors:
