November 11, 2016

Electronics

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

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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



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

Positive probe to negative pin
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

Connect a LOAD (high wattage bulb for AC) in series with the faulty device as shown above. Light will turn ON when power is applied, IF device is shorted.

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