Question:

How to power an old laptop with a 3-pin DC connector? >
> I have a vintage laptop from the late 20th century, a Leading Edge Type 9, that does not have a working battery. I want to use it with a direct current (DC) power supply, but I cannot find the original cable that fits the 3-pin DC port on the back of the laptop. The port looks like this: [PIC_KPP.png](http://kycon.la.coocan.jp/products/dcp/img/PIC_KPP.png), and the cable should look like this: [KPPX-3P.jpg](http://i923.photobucket.com/albums/ad76/NETTUEMsc4V92qMY/KPPX-3P.jpg). >
> Is there any way to obtain or make a compatible cable for this laptop? What are the specifications of the voltage and polarity of the pins? I have some normal wires that I can insert into the holes, but I do not know how to connect them safely and correctly. I also have some technical documents that I do not understand: [KPPX-3P.pdf](http://anacapa.kycon.com/Pub_Eng_Draw/KPPX-3P.pdf) and [Wikipedia article](https://en.wikipedia.org/wiki/DC_connector#3-pin). >
> Any advice or guidance would be greatly appreciated. Thank you.

Answer:

How to power an old laptop with a 3-pin DC connector?

If you have a vintage laptop from the late 20th century, such as a Leading Edge Type 9, you may face some challenges in finding a suitable power supply for it. The laptop does not have a standard DC jack, but a 3-pin DC connector that looks like this:


The original cable that fits this connector is hard to find nowadays, and it looks like this:


So, how can you power your old laptop with a 3-pin DC connector? In this article, we will explore some possible solutions and explain the specifications of the voltage and polarity of the pins. We will also show you how to interpret some technical documents that may help you in this process.

The easiest and safest way to power your old laptop is to find a compatible cable or adapter that matches the 3-pin DC connector. You can try searching online for keywords such as “3-pin DC cable”, “3-pin DC adapter”, “KPPX-3P cable”, or “KPPX-3P adapter”. You may also check some electronic stores or hobby shops that sell vintage or retro devices and accessories.

However, finding a compatible cable or adapter may not be easy or cheap, as they are rare and obsolete. You may also need to verify that the cable or adapter you find has the correct voltage and polarity for your laptop, as using the wrong one may damage your device.

Solution 2: Make your own cable or adapter

Another option is to make your own cable or adapter that fits the 3-pin DC connector. This requires some basic skills and tools in electronics, such as soldering, wiring, and measuring. You will also need some materials, such as a DC power supply, a DC jack, some wires, and a 3-pin plug.

The steps to make your own cable or adapter are as follows:

1. Find a DC power supply that has the same voltage and current rating as your laptop. You can check the label on the back of your laptop or the original power adapter for this information. For example, the Leading Edge Type 9 laptop requires a 12V 2A DC power supply.

2. Find a DC jack that fits the DC power supply. You can use a multimeter to measure the voltage and polarity of the DC jack. The positive terminal should be the center pin, and the negative terminal should be the outer ring. You can also use a polarity tester to check this.

3. Find a 3-pin plug that fits the 3-pin DC connector on your laptop. You can use the same keywords as in solution 1 to search for this. Alternatively, you can use a 3-pin socket and some wires to make your own plug.

4. Connect the DC jack to the 3-pin plug using some wires. You will need to solder the wires to the terminals of the DC jack and the 3-pin plug. You will also need to match the voltage and polarity of the pins. The diagram below shows how to do this:


The red wire connects the positive terminal of the DC jack to the center pin of the 3-pin plug. The black wire connects the negative terminal of the DC jack to the bottom pin of the 3-pin plug. The green wire connects the ground terminal of the DC jack to the top pin of the 3-pin plug. Note that the ground pin is not essential for the laptop to work, but it may help to prevent electrical interference or noise.

5. Test your cable or adapter before using it on your laptop. You can use a multimeter to measure the voltage and polarity of the 3-pin plug. The center pin should have the same voltage as the DC power supply, and the bottom pin should have zero voltage. The polarity should be the same as the DC jack. You can also use a polarity tester to check this.

Solution 3: Use normal wires to power your laptop

The last option is to use normal wires to power your laptop. This is the simplest and cheapest way, but also the riskiest and least reliable one. You will need the same materials as in solution 2, except for the 3-pin plug. You will also need some tape or glue to secure the wires to the 3-pin DC connector.

The steps to use normal wires to power your laptop are as follows:

1. Find a DC power supply and a DC jack that match your laptop’s specifications, as in solution 2.

2. Cut off the DC jack from the DC power supply, and strip the wires to expose the terminals. You should have two wires, one for the positive terminal and one for the negative terminal. You can use a multimeter or a polarity tester to identify them.

3. Insert the wires into the holes of the 3-pin DC connector on your laptop. The positive wire should go into the center hole, and the negative wire should go into the bottom hole. You can use some tape or glue to secure the wires to the connector. Do not insert any wire into the top hole, as it is for the ground pin.

4. Test your wires before using them on your laptop. You can use a multimeter or a polarity tester to measure the voltage and polarity of the wires. They should be the same as the DC power supply.

How to read the technical documents

You may have some technical documents that can help you understand the 3-pin DC connector and its specifications. For example, you may have this document: [KPPX-3P.pdf](http://anacapa.kycon.com/Pub_Eng_Draw/KPPX-3P.pdf), which is a datasheet for the 3-pin plug. You may also have this document: [Wikipedia article](https://en.wikipedia.org/wiki/DC_connector#3-pin), which is a general overview of the 3-pin DC connector.

The datasheet for the 3-pin plug contains some useful information, such as the dimensions, the ratings, and the pin assignments of the plug. You can use this information to find a compatible plug or to make your own plug. The diagram below shows how to read the datasheet:


The dimensions are given in millimeters (mm), and they show the size and shape of the plug. The ratings are given in volts (V), amperes (A), and ohms (Ω), and they show the maximum voltage, current, and resistance that the plug can handle. The pin assignments are given in numbers and letters, and they show the function and polarity of each pin. The center pin is pin 1, and it is the positive (+) terminal. The bottom pin is pin 2, and it is the negative (-) terminal. The top pin is pin 3, and it is the ground (G) terminal.

The Wikipedia article for the 3-pin DC connector contains some general information, such as the history, the applications, and the variations of the connector. You can use this information to learn more about the connector and its uses. The diagram below shows how to read the article:


The history section gives some background information on the origin and development of the connector. The applications section gives some examples of devices that use the connector, such as laptops, printers, and scanners. The variations section gives some details on the different types and models of the connector, such as the KPPX, the KPP, and the KPPC.

Conclusion

In this article, we have discussed how to power an old laptop with a 3-pin DC connector. We have presented three possible solutions: finding a compatible cable or adapter, making your own cable or adapter, and using normal wires. We have also explained how to read some technical documents that can help you in this process. We hope that this article has been helpful and informative for you. Thank you for reading.