This article is taken from the Seminar given by Todd "PinTed" Andersen at the October 2005 Pinball Circus held at SS Billiards.  In it, Todd explains all about transistor theory and operation, and how that relates to their use in pinball machines. There is also a test at the end to check your understanding.

If you would like to follow the seminar yourself, the parts needed are listed along with sources and a printer-friendly version of this article is included in Word format.

Pinball Transistor Testing - Testing transistors used in pinball machines.

1) Introduction

About your instructor; Todd Andersen, (A.K.A in the pinball hobby as “PinTed”) holds an Associates Degree in Electronics Technology from Northwester Electronics Institute (NEI). He was the pinball technician on a coin-op route for CDL Music and Games ( CDL ). He ran his own business performing in-home repair of pinball machines (Pinball Renaissance). Todd is continuing his education in microelectronics with the company he currently works for, Guidant.

2) Purpose of This Seminar

This seminar was put together as a response to all of the technical questions asked about transistors (identification, substitution, replacement) that keep appearing on the pinball newsgroup – RGP. This basic seminar will answer some of the questions that constantly reoccur on the group. This seminar will safely teach anyone who has completed these classroom materials by reading the materials and following the hands-on exercises the following: basic transistor identification, substitution, troubleshooting, and replacement. The specific purpose of this fourteen-part introductory seminar is to teach some basic:

• Electrical Safety
• ESD Protection Basics
• DMM Instructional Basics
• Transistor History
• Use of Transistors in Pinball
• Resistor Basics
• Diode Physics
• Transistor Physics
• Transistor Identification
• Transistor Testing
• Transistor Troubleshooting

This seminar has been laid-out for the web from the original printed material. There is also a printer-friendly version available at the bottom of the article which is intended to be printed on only one side of each page. This is to allow the other side free for note taking.

3) Electrical Safety

This seminar starts with electrical safety because safety is the most important part for you to remember. Safety is the first responsibility - both for yourself and for the people using your pinball machine.

To ensure that you do NOT get and electrical shock, ensure that your pinball machine is plugged into a property grounded three-prong circuit. This type of circuit can be verified with a circuit tester. If the electrical circuit is not properly grounded, you must call a qualified electrician to correct this potentially lethal problem.

Rule #1) Safety first!

Rule #2) As little as 0.25 or 1/4Amp of electricity is lethal. So, if you don't know how much current you are dealing with – STOP.

Rule #3) It is best to, unplug a pinball machine, remove the main fuse, and plug the game back in, before touching on a pinball machine's circuit board(s).

Remember: The proper way to handle any circuit board is to pick it up by its edges.

4) ESD Protection

This material includes ESD protection because it is the most important aspect, for the components themselves, in handling any electronic component. And, is probably the most overlooked part in dealing with all electronic components.

Rule #1) A charge of as low as 100.0 Volts can damage an electronic component.

Rule #2) The discharge of 3,000.0 Volts or greater can be felt by most people.

Rule #3) The discharge of 6,000.0 Volts or greater can be heard by most people.

Rule #4) The discharge of 8,000.0 Volts or greater can be seen by most people.

Electrostatic charge is any electrical field on a body. Simply walking across a carpeted floor can generate the filed. This type of charging is done through triboelectric effect. The charge may usually safely be put to ground potential by simply touching “ground”. This is aptly called “grounding”. You may “ground” yourself by touching a playfield glass rail of a properly grounded pinball machine; which is plugged into a properly grounded circuit. Once you and the machine (and its internal boards) are grounded; there is usually no potentially harmful field present.

5) Transistor History

Today, we will mainly be talking about one type of solid-state electronic device, the bipolar (or junction) transistor, which was invented on December 23rd, 1947 by Bell Laboratories. Prior to the invention of transistors, tubes were used in electronic circuits.

6) Transistors in Pinball

Transistors were seldom used in pinball machines prior to the 1970's. And, instead of vacuum tubes: motors, solenoids, relays, and switches were used to control all of the functions of a pinball machine. This type of pinball machine is commonly referred to as electromechanical.

7) DMM Basic Instructions

7a) Information:
Digital Milti-Meters, nicknamed DMMs, can be used to test components and boards inside a solid-state pinball machine. The use of DMMs is preferred because they are a hand held piece of test equipment that has many features for testing and troubleshooting pinball boards. As with electronic components, many different manufacturers make may different types and styles of DMMs. So, the following instructions will try to include many types of DMMs.

For Safety's Sake: Always remember to keep your hands on the plastic, insulated part of your DMM lest leads (or probes) and away from the shinny metal points!

Also, be sure to contact ONLY the component under test with the test lead tips.

7b) Hands-on:

1. Bring out your DMM.
   
2. Insert the plug of the RED test lead into the jack that is labeled: “RED”, and/or “+”, and/or “V”, and/or “Ohm”, and/or the Greek symbol “O” (omega).
   
3. Next insert the plug of the BLACK test lead into the jack that is labeled “BLACK” and/or “-”, and/or “Gnd”, and/or with the symbol (ground).
   
4. Turn on and/or set your meter to read Ohms or Resistance . Set your DMM to measure the smallest scale or smallest reading. I.E. 100 Ohms – Not 1000 ohms.
   
5. Now, touch and hold the points or probe ends of your test leads together.
   
6. You should see: “0” or “0.0X” (where the letter “X” is representing any number of “0”s) in your meter's display. This represents a reading of no (zero) ohms, or no opposition to the flow of electricity. But, you will probably see some small number followed by a decimal point ( . ) and a few other digits. (i.e. 3.4 Ohms)
   
7. Now, set and leave your test leads on the table.
   
8. Your meter should read: “OL”, or “OOL”. Or your meter's display may simply “flash”. And/or your display my flash “OL”, or “OOL”.
   
9. Set your DMM to the side but leave it set-up in this condition.

8) Resistor Basics

8a) Information:
Resistors are passive electronic components that impede the flow of electrical current. A resistor is measured in Ohms and is rated in Watts. The greater the ohmic value of a resistor, the greater its ability to impede the flow of current. Like transistors, there are many kinds and types of resistors. As this is a transistor seminar, we will not be covering this device in this seminar. But, we will be using a resistor as part of the seminar.

The symbol that looks like a mountain range on the horizon is the schematic symbol for a passive resistor and is shown directly below.

Resistor

This component has no polarity and can be put into a circuit in either direction.

8b) Hands-on:

1. Open your ESD safe bag of electronic components and take out all of the devices.
   
2. Pick out only the components that have axial leads and replace all others.
   
3. Now, put away the components that are the least colorful.
   
4. Two electronic components should be left. These are resistors.
   
5. Chose the resistor with the following color bands: BROWN, BLACK, and RED.
   
6. Put the tip of your RED test lead on one lead of the resistor.
   
7. Put the tip of your BLACK test lead on the other lead of the resistor.
   
8. You should get a reading of around 1,000 Ohms. Your reading may be expressed in a metric prefix “ K ” i.e. 1.0 KOhm. And, just like your previous “zero Ohm” test, your value may not be exactly 1,000 Ohms. (i.e. 1.12 Kohm)
   
9. Now test the other resistor with the following color bands: BROWN, BLACK, and GREEN.
   
10. You should get a reading of around 1,000,000 Ohms. Again, your reading may be expressed in a metric prefix. i.e. 1.0 MOhm. And again, just like in the previous resistor test, your value may not be exactly 1,000,000 Ohms. (i.e. 1.19 MOhm)
    
11. Did your reading fluctuate? If so, you may have ignored the above safety warning and put your fingers in the circuit. This can be a costly mistake.

Again, FSS: Always remember to keep your hands on the plastic, insulated part of your DMM test leads (or probes) and away from the shinny metal points!
Also, be sure to contact ONLY the test lead tips with and circuit under test.

9) DIODE PHYSICS

9a) Information:
Again, like transistor, there are many kinds and types of diodes. A diode is an active solid-state device that controls the flow of electrical current. The current is controlled by a single junction made up Negative (N) and Positive (P) regions inside the body of the diode. Germanium (Ge) diodes usually have a junction forward voltage drop (Vf) of approximately 0.2 to 0.4 Volts. Where as, silicon ( Si ) diodes usually have a junction forward voltage drop (Vf) of approximately 0.5 to 0.7 Volts. The symbol that looks like the letter “T” that is being split by an arrow is the schematic symbol for a diode and is labeled and shown directly below.

9b) Hands-on:

1. Open your ESD safe bag of electronic components and take out all of the devices that have two axial leads.
   
2. Pick out only the components that have axial leads and replace all others.
   
3. Now, pick the components that are NOT the two resistors.
   
4. Two electronic components should be left. These are diodes.
   
5. Choose one of the diodes.
   
6. Set your DMM to “Diode Check” and/or
   
7. Put the tip of your RED test lead on one lead of the diode.
   
8. Put the tip of your BLACK test lead on the other lead of the diode.
   
9. You may have gotten a reading of around 0.2 up to 0.7 Volts.
   
10. Now reverse the leads. You may have gotten a reading of “ 0L ” or 0.0 Volts.
    
11. With the leads one-way the diode's N (negative) / P (positive) junction is forward biased. This is the small voltage reading of 0.2 to 0.7 Volts. The diode gets biased when the positive lead (RED) is on the positive (P) half of the diode junction and the negative lead (BLACK) is on the negative (N) half of the diode junction. With the leads the other way, the diode cannot operate, or blocks current. This is the reading of 0L or 0.0 Volts.
    
12. Now test the other diode.
    
13. Try the test leads each way.
    
14. When biased, the Germanium (Ge) diode should have given a reading of 0.2 to 0.4 Volts.
    
15. When biased, the silicon (Si) diode should have given a reading of 0.5 to 0.7 Volts.
    
16. When un-biased (open) both diodes should have given a reading of “0L” or 0.0 Volts.

10) TRANSISTOR PHYSICS

10a) Information:
There are many kinds and types of transistors. A transistor is a solid-state device that controls the voltage level in and electronic circuit. The voltage is controlled by two junctions made up of Negative (N) and Positive (P) regions inside the body of the transistor. Germanium (Ge) transistors usually have a junction voltage drop of approximately 0.2 to 0.4 Volts. Where as, silicon (Si) transistors usually have a junction voltage drop of approximately 0.5 to 0.7 Volts.

The transistor's prefix "2N" denotes the number of junctions the transistor device has.

Base = The base; where everything starts.
Collector = The base collects electrons from the collector.
Emitter = The base emits electrons to the emitter.

There are two paths for current to flow in a transistor, one part for each junction. There is a base-collector path and a base-emitter path. The schematic symbol for a NPN transistor is shown below with its labels.

10b) Hands-on:

1. Open your ESD bag and take out all of the devices that have three radial leads.
   
2. Pick out only the components that have radial leads and replace all others.
   
3. Now, pick the components that are the smallest, black-bodied components.
   
4. Two electronic components should be left. These are transistors.
   
5. Choose the transistor with the straightest leads.
   
6. Set your DMM to “Diode Check” and/or
   
7. Put the tip of your RED test lead on one lead or leg of the transistor.
   
8. Leave your RED test lead in place and put the tip of your BLACK test lead on another leg of the transistor.
   
9. Still keep your RED test lead in place and put the tip of your BLACK test lead on the other leg of the transistor.
   
10. You may have gotten a reading of around 0.5 up to 0.7 Volts.
    
11. If not, reverse the RED and BLACK leads and start again.
    
12. Now, you may have gotten a reading of around 0.5 up to 0.7 Volts.
    
13. If not, keep changing test configurations until you can keep the DMM's RED test lead in place and get a reading of 0.5 up to 0.7 Volts when touching the BLACK test lead to either of the transistor's other leads.
    
14. Just as when you tested the diodes with your DMM, you electrically biased the N (negative) P (positive) junctions of the transistor. And, just as with the diodes, with the leads the other way, the junctions cannot be biased.

11) Transistor Identification

11a) Information:
Transistors have two main parts, the body and the leads. All pinball transistors have three leads. As previously stated, “The prefix '2N' for a transistor denotes the number of junctions the transistor device has.” But different manufacturers could not name the transistors the same without having to pay royalties. Therefore, different manufacturers use different nomenclatures. Just as there are many different transistor manufacturers, there are many different types of transistor. The name of the transistor is written on its body. With some experience, the type of transistor may be known by its name.

Transistor Type Chart

To make learning easier, we are going to primarily stay with the NPN bipolar transistor.

Question, What is the meaning of the car's name – “Trans Am”?
The prefix “Trans” is Latin for “across”.
And the suffix “Am” is an abbreviation for “America”
So, the answer is, “Across America”.

The same is true for the word “transistor”
The prefix “trans” is again Latin for “across”.
And the suffix “istor” is taken from “resistor”
So the answer is, “across resistance”, the crossing from a maximum resistance to a minimum resistance. A transistor is a combination of the resistors and diodes that you already tested. Through use of its Negative ( N ) and Positive ( P ) junctions, a transistor can change from being a 1MOhm resistor to being a 1KOhm resistor.

Going back to the example of a car, a transistor has “specks”; just like a car.

Specification Chart

Now, look at the following chart to see two types of transistors. Notice the similarities and the differences.

11b) Hands-on:

1. Open your ESD safe bag and take out the two smallest transistors.
   
2. Chose the transistor with straight leads.
   
3. Use the chart (below) to see which transistor you have chosen.
   
4. You should have verified that this is a 2N3904 transistor.
   
5. From reading the labeling and using the chart (below), you should have concluded that the transistor was probably a general-purpose type.
   
6. Now use your DMM to test the transistor with the method you have just learned.
   
7. From testing the junctions, you should have gotten a reading of 0.5 to 0.7 Volts and concluded that the device is a NPN, silicon transistor. You should have also concluded that the base is the center lead.

Bipolar Transistor Chart

For ease of replacing transistors while repairing pinball machines, transistor substitution or “cross reference” charts have been included for your reference.

As additional hands on learning, use the following reference charts and your new electronic component testing skills to determine the other transistor in your ESD bag.

Transistor Cross-Reference Charts

General Purpose Transistors

General Purpose Transistors

Darlington Transistors

Darlington Transistors

Power Transistors

Power Transistors

High Power Transistors

High Voltage Transistors

12) TRANSISTOR TROUBLESHOOTING

12a) Information:
A blown fuse on a pinball machine's solenoid driver board is a good indication of a blown transistor on that board.

Use your transistor checking skills to troubleshoot a blown transistor. First verify the failure and then replace the transistor. When replacing the transistor you many go up in voltage or current ratings, but you MUST stay with the same type of transistor. The rule of thumb for rating of a transistor is “double up”.

And, it is a good idea to “shotgun” all associated components. (i.e. pre-drive transistor, drive transistor, blocking diode, “bootstrap” diode, resistors and capacitors.)  At a minimum, it is recommended that the: pre-drive transistor, drive transistor, and “bootstrap” diode all be replaced.

Lastly, replace the blown fuse with a properly rated fuse. Do NOT automatically replace the fuse with one identical to the blown fuse. As someone was probably “in” the pinball machine before you got there, it is best to check the game's manual and insert the recommended fuse.

12b) Hands-on:

1. Open your ESD safe bag and take out the transistor with its leads twisted together.
   
2. Gently untwist the leads (counterclockwise).
   
3. Verify than none of the leads are touching.
   
4. From reading the package and observing its small size, you should have concluded that the transistor was a 2N3904 general-purpose type.
   
5. Use your transistor checking skills to troubleshoot this transistor.
   
6. You should have verified that this as an NPN transistor.
   
7. You should have discovered that the transistor is shorted Base to Collector.
   
8. From testing the junctions, you should have concluded that the transistor's Base to Emitter junction is silicon (Si).

13) GLOSSARY

Ampere - Almost always shorted to “Amp”, Amperage is the amount of current flowing inside a circuit.

Axial Leads - of an electronic component that appear as though they go through the entire device body. (Think of the axel on a car.)

Blocking Diode - A diode, used to isolate the solenoid drive components from the rest of the circuit.

Bootstrap Diode - A diode, used to protect the solenoid drive components from the inductive kick produced when a solenoid turns off.

CEMF - Counter Electro-Motive Force. (See inductive kick.)

Current - Measured in Amperes, current is the flow of electricity in an electronic circuit. (Think of electrical current as the flow of water in a river. The wider the river, the greater the amount of flow.) Safety rule - amps kill!

Drive Transistor - The transistor used to turn on a solenoid or light.

DMM - An acronym for, “Digital Multi-Meter”. This is a piece of hand held test equipment that allows the testing and troubleshooting of electronic components and circuit boards.

Electrical Field - An electrical force, made by a charge on the surface of an object.

ESD - An acronym for, “Electrostatic Discharge”. This is the transfer of charges between objects at different potentials. (Think of when you get “zapped” getting out of your car in winter.)

Flash - The turning on-and-off of a: circuit, device, or display.

Fluctuate - To change wildly from one reading or measurement to another.

FSS - An acronym for, “For Safety's Sake”. Safety is: the first, and most important, and largest concern in dealing with electronic components and/or boards.

Inductive Kick - The counter electrical force produced when a solenoid turn off. This force (voltage) can be many times greater than the voltage level that turned the solenoid on. (Think of a swirling current away from the main current in a river.)

K - The metric prefix “Kilo”. The Greek “ K ” stands for the number, one thousand.

Lead - The metal part of and electronic component used to secure and solder that component in place.

M - The metric prefix “Mega” (abbreviated “Meg”). The Greek letter “ M ” stands for the number, one million.

Ohm - A unit of opposition to the flow of electrical current.

OL - An acronym for, “Over Limit”. This is a condition where your DMM cannot make a measurement because what it is trying to measure is too large a value to report.

OOL - An acronym for, “Out Of Limits”. This is the same as “OL”.

Pre-Drive Transistor - The transistor situated before the drive transistor that is used to turn on the drive transistor.

Radial Leads - of and electronic component that protrude out of the body of an electronic device. (Think of the tines on a fork.)

Voltage - Measured in volts, voltage is the electrical pressure inside an electronic circuit. (Think of voltage as the swiftness of the water in a river. The faster the current, the greater the amount of force.) Safety rule - volts hurt!

Watt - A unit measuring the flow of electrical current at a certain voltage.

ELECTRONIC COMPONENTS LIST

PLACES TO BUY

Because the seminar was given locally, a local electronic parts supplier was named. But others are mentioned. Of the suppliers listed, Great Plains Electronics is preferred.

TECHNICAL REFERENCES

14) PINBALL TRANSISTOR

Test 14a) Information:
This test is PASS or FAIL. You must get ten or more correct answers (83%) to PASS. Read each question carefully. Some questions require a written answer, while others are fill-in the blank, and others have multiple choices. This is an open book test.

14b) Hands-on:
Complete the following twelve questions.

15a) TEST

Date: _______________________

Student's First Name and Last Initial: ________________________

Pinball Transistor Testing - Testing transistors used in pinball machines.

Q1) What are the two most important things to remember when working with any electrical circuit?

A1a) _____________________________________________________________ A1b) _____________________________________________________________

Q2) What is the greatest consideration for any electronic component?

A2) ______________________________________________________________

Q3) Fill in the blanks:

A3a) __________ hurt. A3b) __________ kill.

Q4) How should circuit boards be picked up?

A4) ______________________________________________________________

Q5) When was the transistor invented and by whom?

A5a) __________ __________, __________ A5b) __________ __________

Q6a) For a silicon diode, what is the two-letter abbreviation for that element?

A6a) __________ __________ (One blank for each letter)

Q6b) For a silicon diode, what is the expected nominal forward voltage drop?

A6b) __________ to __________ Volts

Q7) For an NPN bipolar transistor, which letter represents the base lead?

A7a) The first (left) “N”
A7b) The “P”
A7c) The second (right) “N”

Q8) For an NPN bipolar transistor, which does the arrow point to?

A8a) Positive (P)
A8b) Negative (N)

Q9) For an NPN bipolar transistor, which lead contains the arrow?

A9a) The Emitter “E”
A9b) The Base “B”
A9c) The Collector “C”

Q10) For an NPN bipolar transistor, which junction has the largest forward voltage drop?

A10a) The Emitter-Collector, “E-C”
A10b) The Base-Collector “B-C”
A10c) The Base-Emitter “B-E”

Q11a) For a NPN bipolar transistor with a short, what is the reading (measurement) of the forward voltage of its shorted junction?

A11a) __________ Volts

Q11b) For a NPN bipolar transistor with a short, what is the reading (measurement) of the reverse voltage of its shorted junction?

A11b) __________Volts

Q12) What is the most important thing to remember when dealing with electricity?

A12)_____________________________________________________________

15b) ANSWERS

Pinball Transistor Testing - Testing transistors used in pinball machines.

A1) Any two of the following are acceptable for A5a) or A5B).
Safety Safety first Be safe Stay safe Stop if you are unsure Stop if you don't know what to do Stop if you don't know what you are doing

A2) Any one of the following is acceptable. ESD ESD protection Grounding

A3) Fill in the blanks: A3a) Volts hurt. A3b) Amps kill.

A4) Any one of the following is acceptable. By its edges Carefully With power removed

A5) Only the following is acceptable for when.
A5a) December 23rd, 1947
Only the following is acceptable for whom.
A5b) Bell Laboratories

A6) Only the following is acceptable.
A6a) S i
A6a) 0.5 0.7

A7) Only the following is acceptable.
A7b) The “P”

A8) Only the following is acceptable.
A8b) Negative (N)

A9) Only the following is acceptable.
A9a) The Emitter “E”

A10) Only the following is acceptable.
A10c) The Base-Emitter “B-E”

A11) Only the following is acceptable.
A11a) 0 (zero, no)
A11b) 0 (zero, no)

A12) Only the following is acceptable. Safety !

A Word document of this seminar in a printer-friendly format is also available.
Click here for the seminar , click here for the cover and click here for the index.

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