Warm greetings from the Elwar Braja blog, everyone! This time, I’m starting redraw project 001 from my PCB kit collection with a simple transistor tester based on a classic circuit. It’s designed to help determine whether the transistor being checked is good or faulty.
The circuit can test both NPN and PNP transistors. What makes it interesting is the use of a flip-flop signal and two LEDs to indicate the transistor’s condition, so you can see the result without dealing with complicated readings.
Table of Contents
Origins of the Tester Circuit from an 80s PCB Kit
This schematic comes from a collection of DIY PCB kits from the 80s and 90s, specifically a kit that circulated during the 80s. Back then, buying a PCB kit usually meant receiving an old printed document that helped you identify the circuit and assemble its components. As time passed, those sheets became harder to find, and the related PCB kits became rare as well.
For me, this circuit deserves a place in the digital archive because its purpose is closely connected to electronics repair work. Transistors appear in all kinds of circuits, so a tool for checking their condition has practical value while also preserving a small piece of electronic kit-building history.
This redraw project is my attempt to bring that technical information back in a digital format that’s easier for today’s generation to read and preserve. The schematic artwork, component numbering, and layout are my own work as Elwar Braja, redrawn from the connections between components rather than copied from the original document.
Archives like this also remind us that learning electronics once began with little more than a PCB, a bag of components, and a single instruction sheet. Digital documentation wasn’t always available to search later, so preserving information about classic circuits is a small but important job that can be done one project at a time.
What Is This Circuit and What Does It Do?
This circuit is used to determine whether a transistor is good or faulty. It can check either an NPN or PNP transistor, with the test result shown through LED 1 and LED 2. You can then compare the display with the indicator pattern specified for the circuit.
In simple terms, the LEDs work like two signal lamps. If LED 1 lights or flashes, the NPN transistor under test is considered good. If LED 2 lights or flashes, the PNP transistor under test is considered good.
There’s also a condition where LED 1 and LED 2 either both light or both remain off. According to the circuit notes, either result indicates that the NPN or PNP transistor under test is faulty. So, reading the result isn’t only about which LED is active. You also need to notice whether it remains lit, flashes, or matches the state of the other LED.
The circuit operates from 9VDC. It’s intended as a condition checker, so its main purpose is to provide an LED indication based on the type and condition of the transistor being tested.
Transistor Tester Schematic Preview
[PLACEHOLDER: Preview gambar skema]
PCB Layout Preview
[PLACEHOLDER: Preview gambar PCB layout]
How to Test a Transistor with This Circuit
Looking at the connections between the components, the circuit generates a flip-flop signal. That signal is then passed to the transistor under test to help determine its condition. LED 1 and LED 2 provide the result as a visual indication.
You can think of the flip-flop action as two alternating states. In this circuit, that signal forms part of the testing process, while the transistor under test affects what appears on the LED indicators. This is a general description based on the function given in the circuit information, not a component-by-component explanation of every stage.
For an NPN transistor, watch LED 1. If LED 1 lights or flashes, the NPN transistor is considered good. If both LEDs light or both remain off, the result indicates that the transistor is faulty.
For a PNP transistor, watch LED 2 instead. If LED 2 lights or flashes, the PNP transistor is considered good. If LED 1 and LED 2 both light or both remain off, the PNP transistor is considered faulty.
When checking a transistor, observe the indicators carefully so you don’t confuse a steady light with a flashing one. Use a 9VDC supply as specified by the circuit information, then read the result according to the LED patterns described above. If the indicators behave differently, don’t draw a conclusion until you’ve checked the circuit and testing procedure again.
Main Component List
The main components listed for this circuit are a 9014 transistor, resistors, LEDs, diodes, and electrolytic capacitors. The table below only includes the component groups available in the circuit information.
| Component | Description | Datasheet | Purchase |
|---|---|---|---|
| 9014 Transistor | 9014 Transistor | View Datasheet | Buy Component |
| Resistor | Resistor | [Lihat Datasheet] | [beli] |
| LED | LED | [Lihat Datasheet] | [beli] |
| Diode | Diode | [Lihat Datasheet] | [beli] |
| Electrolytic Capacitor | Electrolytic Capacitor | [Lihat Datasheet] | [beli] |
⚠️ Test Before Building
This schematic is a redraw based on an old physical document, and not every part of it has necessarily been tested directly. Before making a permanent PCB, check the circuit in stages so any possible errors can be found early.
- Stage 1: Run a software simulation first if possible, using tools such as Proteus, LTSpice, or the EasyEDA simulator.
- Stage 2: If the circuit characteristics allow it, assemble a physical prototype on a project board or breadboard before moving to a permanent PCB. If the circuit isn’t suitable for a breadboard, use another safe and appropriate prototyping method.
- Stage 3: Only proceed with making and assembling the permanent PCB after you’re confident that the circuit connections and indicator results are correct.
Check every component connection again, and don’t assume that a redraw is automatically free from mistakes. Elwar Braja is not responsible for losses of any kind arising from the assembly process, testing, component use, or operation of this circuit.
Even so, I still encourage you to try it carefully and one stage at a time. Please share your results in the comments, whether this simple transistor testing circuit works or you find something that needs correcting. Your feedback can help improve this growing archive of classic circuits.
Download the Full HD Schematic
HD SCHEMATIC ACCESS
Preparing access — 10s remaining
10sThe button becomes available after the countdown finishes.
Closing Thoughts
This first redraw project is the starting point for collecting traces of old circuits from DIY PCB kits of the 80s and 90s. The transistor tester has a simple purpose, but it remains interesting because it uses a flip-flop signal and LED indicators to check the condition of both NPN and PNP transistors.
If you’ve built a similar tool or have experience with a simple way to test transistors, tell everyone about your process and results in the comments. Corrections, assembly notes, and testing experiences are also valuable for keeping this classic electronics archive useful to other folks.
The schematic in this project was independently redrawn from a classic electronic circuit that has circulated widely through various sources for many years. The circuit and component values are common technical knowledge. The schematic artwork, PCB design, and Gerber files are the work of elwarbraja.com. This project is not affiliated with any brand or manufacturer.
FAQ About This Tester
How can I tell if an NPN transistor is still good?
With this circuit, an NPN transistor is considered good if LED 1 lights or flashes. If LED 1 and LED 2 both light or both remain off, the transistor is considered faulty.
How do I check a PNP transistor using LEDs?
A PNP transistor is considered good if LED 2 lights or flashes. If both LEDs light or both remain off, the PNP transistor is considered faulty.
What supply voltage does this circuit use?
This circuit operates from 9VDC. Use that voltage when running a simulation or testing a physical prototype.
Has this schematic been tested directly?
Not every schematic in this redraw project has been tested directly. Run a simulation first, continue with a physical prototype if possible, and only use a permanent PCB after you’re confident the circuit works.
What does the flip-flop signal do in this tester?
The circuit generates a flip-flop signal that is passed to the transistor under test. The result is then observed through the lighting or flashing pattern of LED 1 and LED 2.
EB / Discussion
0 Comments