Ohms Law
I = V / R
V = I x R
R = V / I
mA = V / Kohms
uA = V / Mohms
Kohms = V / mA
mW = V x mA
V = Kohms x mA
V = Mohms x uA
M (mega) = 1,000,000
K (kilo) = 1,000
m (milli) = .001
u (micro) = .0000001
Power in Watts
P = V x I or Watts = V x I
I = P / V
V = P / I
I = W / V
Watts = Horsepower x 746
Watt-hours = Amp-hours × Volts
Amp-hours = Watt-hours / Volts
Parallel Circuit
Voltage is the same across all branches.
Total Resistance must be less than the smallest branch Resistor.
Main line current is divided into branch currents.
The largest branch I is in the smallest parallel Resistor.
Open in one branch does not prevent current in other branches.
Series Circuit
Current is the same in all components.
Total Resistance must be more than the largest individual Resistor.
Applied voltage is divided into IR voltage drops.
The largest IR drop is across the largest series R.
Open in one component causes entire circuit to be open.
Identifying PNP transistors / BJT (Bipolar Junction Transistor)
Transistor 2N3906
Using a Digital Multi-meter set at DIODE Mode
Forward bias: Negative probe to Base (pin 2) & Positive probe to Emitter (pin 1) = value is 0.717 volts
Reversed bias: Reading would be OL (Over Limit)
Forward bias: Negative probe to Base (pin 2) & Positive probe to Collector (pin 3) = value is 0.711 volts
Reversed bias: Reading would be OL (Over Limit)
This transistor is a PNP
Emitter = Pin 1 (will always have the higher value)
Base = Pin 2
Collector = Pin 3
NOTE:
The most important voltage to be measured on a transistor is the bias voltage between Base & Emitter. This voltage will generally range:
Below 0.7v for Silicon Transistor
Below 0.2v for Germanium Transistor
Below 0.5v for Driver Transistor
----------------------
Identifying NPN transistors
Transistor 2N4401
Using a Digital Multi-meter set at DIODE Mode
Forward bias: Positive probe to Base (pin 2) & Negative probe to Emitter (pin 1) = value is
0.587
Reversed bias: Reading would be OL (Over Limit)
Forward bias: Positive probe to Base (pin 2) & Negative probe to Collector (pin 3) = value is
0.584
Reversed bias: Reading would be OL (Over Limit)
This is an NPN Transistor
Emitter = Pin 1 (will always have the higher value)
Base = Pin 2
Collector = Pin 3
NOTE: Forward bias voltage is between 0.3v to 0.7v
TO TEST MOSFET
Digital multi meter set to Diode mode
Positive probe to Gate; Negative probe to Drain: Reading OL (Good)
Negative probe to Gate; Positive probe to Drain: Reading OL (Good)
Positive probe to Drain; Negative probe to Source: Reading OL (Good)
Positive probe to Source; Negative probe to Drain: Reading .3v to .9v (Good)
Positive probe to Drain; Negative probe to Source: Reading beeps (Shorted)
NOTE: N channel mosfet Gate voltage is always higher in order to operate
On state method test (Good)
Negative probe to Source
Positive probe touch to Gate briefly (no beep)
Positive probe move to Drain briefly (beeps)
Touch Gate & Drain with finger to discharge Mosfet
Positive probe to Drain; Negative probe to Source: (no beep - Good)
On state method test (Bad)
Negative probe to Source
Positive probe touch to Gate briefly (beeps)
Positive probe move to Drain briefly (beeps)
Touch Gate & Drain with finger to discharge Mosfet
Positive probe to Drain; Negative probe to Source: (beeps - Shorted)
To test 8-Pin P-Channel Mosfet with Analog Multi-meter on Rx10
.JPG)
Short pins 3 & 4 to set Mosfet Off State
Positive probe to Source; Negative probe to Drain: low R
Negative probe to Source; Positive probe to Drain: high R
Positive probe to Gate; Negative probe to Drain: high R
Positive probe to Gate; Negative probe to Source: high R
Negative probe to Gate; Positive probe to Source: high R
To test 8-Pin P-Channel Mosfet with Digital multi-meter on Diode mode
Short pins 3 & 4 to set Mosfet Off State
Negative probe to Gate; Positive probe to Drain: to set Mosfet ON State
Positive probe to Drain; Negative probe to Source: displays voltage reading
Negative probe to Drain; Positive probe to Source: displays voltage reading
How to test a MOSFET with a multi-meter:
https://www.youtube.com/watch?v=fRl8mZ1Y7dk
https://www.youtube.com/watch?v=j1vW4TsKc8U
https://www.youtube.com/watch?v=RkWy1EirEu8
Diodes
Diode in Series
Current rating remains the same.
Voltage rating increases.
Diode in Parallel
Current rating increases.
Voltage rating remains the same.
Common defects of diode
Forward bias:
Zero reading = means SHORTED
Infinite reading = means OPEN
High reading = means LEAKY
Reverse bias:
Zero reading = means SHORTED
High reading = means LEAKY
Low reading = means LEAKY
Testing High Voltage Diode
How to test a bridge rectifier with Digital Multi-meter
Negative probe to + pin = 1.00v
Negative probe to pin 2 = .550v
Negative probe to pin 3 = .542 v
Negative probe to negative pin
Positive probe to + pin, pin 2, pin 3 = All OL reading
How to test an optocoupler
https://www.youtube.com/watch?v=_0FRnI7gveo
To test electronic device which shuts down immediately when power is turned ON
Capacitance Tolerance
Ceramic disk capacitors = +/- 20%
Paper capacitors = +/- 10 %
Mica or Tubular = +/- 2 to 20 %
Silver-plated Mica = +/- 1 %
ESR Electrolytic Capacitor Table
Resistor Color Coding
Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Gray = 8
White = 9
3rd band is the decimal multiplier, giving the number of zeros after the 2 digits.
Black for the 3rd stripe means DO NOT ADD any zeros to the first 2 digits.
When the 3rd stripe is GOLD, multiply the first 2 digits by 0.1
When the 3rd stripe is SILVER, multiply the first 2 digits by .01
When 4th stripe is GOLD or SILVER, it indicates how accurate the resistance value in tolerance.
GOLD = 5% Tolerance
SILVER = 10% Tolerance
When there is no 4th stripe, the Tolerance is 20%.
Conversion/multiplier:
M (mega) = 1,000,000
K (kilo) = 1,000
m (milli) = .001
u (micro) = .000001
Examples:
5 mega ohms x 1,000,000 = 5,000,000 ohms
5,000,000 ohms / 1,000,000 = 5 mega ohms
18 kilo volts x 1,000 = 18,000 volts
18,000 volts / 1,000 = 18 kilo volts
48 mA x .001 = .048 amps (amperes)
.048 A / .001 = 48 mA
15 uV x .000001 = .000015 volts
.000015 volts / .000001 = 15 uV
5uA x .001 = .005mA
.005 / .001 = 5uA
How to check a bridge rectifier:
https://www.youtube.com/watch?v=llit6P7Uk0Q
How to test a voltage regulator:
https://www.youtube.com/watch?v=qd7Hd1-Q7PM
How to check a capacitor using a digital multi-meter:
https://www.youtube.com/watch?v=vaZ3Evx8poc
Using analog multi-meter set to Ohm meter
Range Rx1 or Rx10
Note: Avoid the Rx1 scale when checking low power transistors.
To check NPN transistor (Silicon)
Forward Bias
B(-) to C(+) = low R means Good
B(-) to E(+) = low R means Good
Reverse Bias
B(+) to C(-) = high R means Good
B(+) to E(-) = high R means Good
To determine Emitter from Collector; Tester set to x10K (Silicon)
C(+) to E(-) = low R
C(-) to E(+) = high R
To determine Emitter from Collector (Germanium)
C(-) to E(+) = low R
C(+) to E(-) = high R
To check PNP transistor (Silicon)
Forward Bias
B(+) to C(-) = low R means Good
B(+) to E(-) = low R means Good
Reverse Bias
B(-) to C(+) = high R means Good
B(-) to E(+) = high R means Good
To determine Emitter from Collector (Silicon)
C(-) to E(+) = low R
C(+) to E(-) = high R
To determine Emitter from Collector (Germanium)
C(+) to E(-) = low R
C(-) to E(+) = high R
