Hello everyone. Today we will be repairing an ASUS K52JR laptop with a faulty keyboard.

Background.

According to the owner, coffee was spilled on the laptop, after which the keyboard stopped working. To get it repaired, the owner took the laptop to a service center where it stayed for several months. In the end, the laptop was returned to the customer without being repaired. The service center workers reported that some expensive component had burned out, and there was no point in buying a new keyboard as it would not work. Additionally, they sold the customer a regular USB keyboard, which they used successfully for several months.

A year after this incident, someone brought me this laptop for cleaning and asked if I could restore the keyboard if possible.

Laptop diagnostics.

I won’t describe the process of disassembling and cleaning the laptop, but I will focus on diagnosing the functionality of the keyboard. Let’s determine if the motherboard is actually faulty or if the problem is only with the keyboard.

When disassembling, I had to pry the keyboard off the case because it was simply glued down with old coffee.

Remnants of coffee on the laptop lid
Same thing on the keyboard

The same thing happened with the laptop lid. Dried sweet coffee had almost permanently glued the DVD drive to the lid.

Coffee on the DVD drive

I began to suspect that the laptop had not even been disassembled, as these traces should have been removed during the repair. The motherboard itself was covered in dust but fortunately not spilled on. There were also no signs of repair on it.

Since it was claimed that a new keyboard had been installed and it didn’t work, I decided to test the functionality of the laptop itself, namely whether the motherboard responded to key presses. For this purpose, I needed to make a small probe.

Making a probe for laptop keyboards. 

The probe will consist of the following parts:

  • 2 thin sewing needles;
  • 2 small wires;
  • one 4.7 kOhm resistor
  • Heat shrink tubing or electrical tape.
Parts for the probe

The process of making it is clearly visible in the photos. The wires are soldered to the needle ears, and the resistor is soldered to the ends of the wires. You can also solder the resistor to the needle and then attach the wire, it’s up to you.

Making the probe.

This won’t affect the device’s performance. For aesthetics, I wrapped everything in heat shrink tubing..

Final version

Testing the functionality of the keyboard connector on the motherboard.

First of all, you need to download a keyboard testing program onto the laptop being tested.

The program interface for keyboard testing.

I am attaching the executable file of the program at the end of the article. Also, make sure that there is access to the connector contacts on the soldering side. If there is no such access, then the laptop needs to be disassembled, and the top cover removed. In my case, there was access, but since the laptop needed to be cleaned, I disassembled the entire laptop.

Now, let’s talk about how to test the functionality. Each pin on the connector is responsible for specific letters and numbers. If we short-circuit several pins with a probe, we will simulate pressing keys on the laptop. The resistor protects the motherboard from short circuits, but its nominal value is sufficient to determine whether a key is pressed.

The computer program will show which keys were pressed and which were not.

Instructions for using the probe.

We place one needle on the first pin of the connector, and then touch the rest of the pins (2,3,4, etc.) one by one with the other needle. Then, we move the first needle to the second pin and touch all the other pins (3,4,5, etc.) with the other needle. We continue in this way until we reach the end of the connector.

Connector for the keyboard. The arrow points to the first pin.
Testing process
This is how the program responds to button presses. The pressed buttons are highlighted in blue, while the buttons that were not pressed are in black.

ВIn the end, if the motherboard is in good condition, all keys will be pressed. In my case, the Scroll Lock, Insert, and second Windows key did not work. This is correct, as these keys are not on my original keyboard.

The program view after short-circuiting the last pin.

Conclusion.

Thus, we have tested the functionality of the motherboard. I ordered a new keyboard, and everything worked perfectly after installation. In the previous service center, they did not even disassemble the laptop, as can be seen from the photo.

Be careful when choosing a service center, and good luck with your repairs!!!

You can download the program to test the functionality of the laptop keyboard here:

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