USB flash drives suddenly not recognized? Unplug the machine!

Support & Help Requests Hardware
#1

This is weird enough, and might save someone else some money, so I had to post it. Maybe someone can explain why it happens.

After months of working flawlessly, my Mate 17.10 machine suddenly did not recognize USB flash drives.

When I inserted a USB flash drive in one of the two, front-panel USB 3.0 ports, nothing happened. Caja didn’t open, I didn’t get a prompt for the encryption password for encrypted drives, and they didn’t appear in lsusb, in my media/user folder, or in Disks. I tested three different USB flash drives, and none worked in the problem machine, though all three drives worked fine in another Mate 17.10 machine.

The USB keyboard and mouse were working fine in the problem machine, as was a USB 3.0 external hard drive. I also tried the back-panel USB ports, and the drives were not recognized there, either, even in the port that worked for the external hard drive.

I hadn’t changed any BIOS or hardware, and I don’t think I ran any updates since the last time the drives were working. Of course, I couldn’t boot a live USB of Mate for additional testing, because a USB drive wouldn’t be recognized.

I plugged a USB mouse into one of the suspect front USB 3.0 ports, and it worked fine, so it didn’t appear to be a problem of dead ports.

I searched high and low and couldn’t find anything that fit, but I finally found a post suggesting that the problem could be electrical. It suggested shutting down the machine, unplugging it from the power supply for a few minutes, then plugging it back in and re-testing. I did so, and now the flash drives are recognized and everything is working fine.

In my area, this time of year, there are frequently power “blips,” where the power goes out briefly and comes back on so quickly it sometimes doesn’t affect digital clocks–but usually does shut down computers–as well as complete power outages. We had a few “blips” between the time the problem machine last recognized USB flash drives and when I found it would not. I guess that may be what caused the problem, but I would certainly like to know the mechanism, and why some USB devices worked fine, but flash drives wouldn’t.

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#2

If BIOS didn’t recognize them either, that sure sounds like a hardware bug. Something locked up in a bad state.

Take it from this old hardware guy - power glitches can create invalid states that would not be possible by normal operation. I spent a career identifying such invalid states and sometimes added recovery logic just in case. A lot of designers never look beyond their truth table.

There’s a standby voltage in most desktops to power things like network cards for Wake-On-LAN (WOL) power control. This voltage only goes off when unplugged. Why it would be involved with USB control is a mystery but I’m not up on all the possibilities.

Just my 2 cents. Good info for someone with similar symptoms.

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#3

Listen to Bill_MI and believe. He is not that old though. :-), that would be me. Power glitches create a totally unknown condition. How far down did the power drop and which chips or gates had a slightly different threshold and ended up in an impossible “truth table” state, from which only a true power down will clear it. Software can not unlock it.

As for waiting a few minutes after unplugging power, 30 seconds is usually 10 times too long. Most power supplies, especially the new switch mode ones have a hold up voltage time of 1 to 2 cycles of power 16 to 32msec (20 to 40msec in the 50Hz world).

I hope you are using good to very good surge suppressor power strips. If you didn’t spend around $25 to $30 each on them they are pretty much worthless. Also if they are from before the 90’s I would be replace them. But even that will not protect you in a brown out, the worst of all cases when the power falls, but not all the way. That is when you end up in the never-never land of gate thresholds creating weird problems and locking out software.

BTW, if it is a laptop, you also have to remove the battery to effect a true power down.

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#4

I have a similar problem except that it is intermittent and affects a USB floppy drive as well as the USB pen drives. The other difference is APC Smart-UPS 750 powering the affected machine and one other. Everything is switched off at night but I don’t unplug unless I’ll be away from home for weeks. Maybe I should.

#5

@Coinneach, your issue doesn’t sound like the same problem I was having, but it wouldn’t cost you anything to try unplugging from the UPS to see if it works to resolve the intermittent issue you’re having with USB.

#6

@Coinneach

Yes

Most people consider power spikes and worry about the over-voltage portion. At the same time there is usually an under-voltage portion. How long is what matters. If it is long enough, it will cause a brown-out and then all bets are off the table. That is when ICs can act outside there normal boundaries and end up in non-truth-table states.

The surge suppression power strips are designed for one thing, STOP the over-voltage, because you can not stop 0 voltage.

Your APC is a good one, but it can only do so much. It is not and cannot be absolutely faultless.

#7

Thank you both for your advice