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I've just purchased a couple of external numeric keypads for my kids' laptops. One is running Lubuntu 20.10, the other is running Ubuntu 20.04, but both are experiencing the exact same behaviour.

On plugging in to the USB port, the num-lock light illuminates and the keyboard works for approximately 1-2 seconds. After that, the light remains on (and num-lock is now enabled on the built-in keyboard), but the external keyboard is non-responsive. Disconnecting and re-connecting makes it work again for the same time period as before.

I've seen various similar posts (especially Keyboard stops working on Ubuntu 16.04 (Xenial Xerus)), as it seemed very similar, but none of the solutions seem to help. Things I've checked (mostly on the Lubuntu system, but I think the Ubuntu one's the same):

  • I'm not running laptop-mode-tools or PowerTop
  • I've located the device in /sys/bus and power/control is set to "on"
  • /power/autosuspend_delay_ms is set to -1000, but setting it to -1 (as suggested by various guides) has no effect.
  • If I toggle num-lock on the laptop keyboard, the light on the external one doesn't change, so it clearly doesn't get updates once it's in its frozen state.
  • Num-lock is only activated on the laptop keyboard after I've pressed something on the numeric pad.
  • Behaviour is exactly the same if the device is plugged in before I power up. The machine works fine. I type a character or two and then the external keypad is dead.

After some experimentation, I think the issue happens a couple of seconds after the first key is pressed and not from plugging it in.

The keyboards both work flawlessly on my desktop Windows machine, so I'm fairly certain this is a software issue. Are there other configuration changes I can try?

Update: Following suggestions in the comments, I've tried running a different O/S from a USB stick. The first that came to hand was PIXEL. The keypads both work fine with a Raspberry Pi Model 3, so it seemed like a good one to try. Interestingly, the behaviour is the same. The keyboards work for a few seconds then stop dead. This suggests to me that it's potentially something in the hardware / firmware and maybe not strictly Ubuntu.

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    Do you have issues if the keyboards are plugged in before the OS is booted? (I have a number of boxes with multiple keyboards; no issues at all, but I'm not plugging any in & out, though I've not noticed any issues on rare occasions I've done that).
    – guiverc
    Jan 23, 2021 at 21:22
  • @guiverc - just tested that and it's no different - have added extra findings to the question. Jan 23, 2021 at 23:40
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    I would try running it on a live system and seeing if the issue occurs (ie. identical hardware but different software/config). I've tried adding second & third USB keyboards and don't have any issues on three PCs locally (using focal & hirsute Lubuntu) with additional keyboards (numerous tried too). Using the live system allows you to see if it's just Lubuntu, but also using different stacks inc. non-Ubuntu based systems.
    – guiverc
    Jan 24, 2021 at 4:55
  • @guiverc - do you mean install a different O/S on the machines to prove the hardware works on those laptops? Jan 24, 2021 at 15:57
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    Using it live allows you to gain more knowledge; ie. the different 18.04 media will let you try original (GA) 4.15, 4.18, 5.0, 5.3, before finally 5.4 kernel also found in 20.04.. Letting you try different kernel & stacks without any install.. I also regularly branch out to non-Ubuntu media too.. You'll learn more where it's a problem, where it works - thus more clues as to what's common & where issue is likely to be. I only tried USB (full) keyboards (3x on 3x boxes in combination) without issues, 20.04 & hirsute (21.04) but do occasionally use them as 2nd so expected they'd work
    – guiverc
    Jan 24, 2021 at 21:12

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