Right Alt Key (Alt Gr) only working every second time

Xenior

6. Oktober 2026 17:08

Hello,

I bought the dual monitor KVM switch (HKS0402A1U-EUBK) around 4 years ago. I used it for a while but then switched back to a single computer setup so I didn't need it for a while. Now I switched back to a two-device setup (one Mac, one Windows device) and therefore set up the KVM again. 

Now after using it for a few days, I recognized that my right alt key (alt gr) is not working properly. I have the following problem:

When typing special letters such as “@” (right alt + l), the letter is only printed every second time I press this combination. Every other time, it just won't print anything. Also, in the case it does work, it spams the letter (e.g. “@”) until I release the right alt key, even if I release the other letter (e.g. “l”) before.

I checked on karabiner elements event viewer, and indeed every second time I only press the right alt key the input is not recognized. What is interesting is that if I hold the right alt key in the scenario where it isn't recognized, as soon as I press an additional key to the right alt key the right alt key press is recognized, but it doesn't result in printed letters, only if I keep holding the right alt key, release the other pressed key and press a different key.

This is really frustrating, because there is no way for me to correct this behavior via any kind of karabiner-element or keyboard software, and I do need the key quite often.

Do you have any suggestions, firmware updates, or configuration changes that could help resolve this behavior?

Kind regards

0

• Offizieller Kommentar

  

  TESmart.01

  30. Oktober 2026 09:22

  Thanks for the detailed explanation! We understand how frustrating this must be, especially when you frequently use the Right Alt (AltGr) key.

  For your HKS0402A1U, we have identified a firmware upgrade that may help resolve this keyboard compatibility issue.

  Since this is an older model, the firmware upgrade requires opening the KVM enclosure to access the internal programming interface.

  You can find the firmware upgrade utility here:

  https://support.tesmart.com/hc/en-us/articles/38945080915737-WCHISPTool-Setup-Firmware-Upgrade-Utility-For-KVM-Models-Requiring-Disassembly
  https://drive.google.com/file/d/14VZWRk0kRoxrRQV2kPAdVOYNpd9l_cv3/view?usp=sharing

  Please note that the upgrade tool runs on Windows only.

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