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PC wouldn't POST yesterday. I notice my USB speakers are flickering and a small external media HDD is clicking.

Unplugged all the USB devices, and it worked, so plugged 'em all in again.

A few hours later I notice my backup external HDD isn't showing. Unplug it, try to plug it in again. I fumble around trying to get it in the USB port, and whenever the USB plug touches the outside of the port, one of my monitors (display port) flickers (partial static/artifacts) and turns off for a moment. Other monitor (HDMI) not affected.

HDD didn't work last night, but have tried it again this morning and it's working. Have done a few more experiments - touching the outside of the port (or even the metal I/O plate at the back) with the powered external HDD USB plug results in flickering. Same result if I do this with my speaker USB plug as well. With the front plate, the minor symptoms above appear - if I do this with the back plate, this can result in the Display Port monitor receiving a black signal for an extended period of time, which resolves when I unplug and plug it in again.

Some things to note:

  • Have recently taken my PC travelling to a LAN, but ensure it travelled on its side to reduce stress on mobo
  • Graphics card (purchased 6 mo ago) seems to sit high in the slot, resulting in the HDMI/DP plugs bumping into the PC case when being plugged in, and not going all the way in. Potentially the metal of the plug was touching the case. Reseated, tilted the card down slightly, and I believe the metal plugs are no longer touching case.
  • Recently did some cable management for my desk, essentially cable-tieing everything (power cables included), however the bundle sits in an area that gets lots of sun - an issue?

I'm unsure if this is a recent issue, or simply one I haven't noticed given that I rarely unplug any of these USB devices.

Specs GA-H170-D3HP motherboard i7 7700 RTX 2010 16GB 2333 RAM Problem HDD: Seagate 4GB external Problem speaker: Logitech G560

Questions:

  1. Is this a big issue?
  2. How should I resolve it? Things to investigate, etc.
  3. Is it safe to continue using this computer and these devices until resolved? Do I risk damage by doing so?
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  • If you take a USB thumb drive and touch the same areas do they do the same thing? The hdd appearing and disappearing sounds like motor failure(I have had that). If you move the speaker and/or hdd to different ports does the problem move with it? Do the devices you plugged into the old ports now have a problem? If only the hdd is plugged in is there a problem? I have seen a bad external power supply make nearby projector unreadable. – cybernard Feb 4 '20 at 13:42
  • @cybernard It doesn't seem to occur when the plugs of other USB devices touch the sockets - only the speakers and HDD. I unplugged everything other than the Display Port monitor and tried touching the HDD and Speaker USB plugs to the sockets - same issue. I've tried using the second Display Port outlet on my video card - same issue. Tried plugging this monitor in via HDMI - no issue. Also no issue with my second screen, which connects via HDMI. – Z H Feb 6 '20 at 4:26
  • I noticed the issue occurring when I plug the power socket into my second monitor while the PC is on. There was a crackle from the 3-pin plug as it went in (typical of all computers I've worked with when wall socket is switched on) and as I did this the symptoms occurred again on the Display Port monitor. Opened up the case and tried unscrewing the motherboard to check everything's okay - and I found that I couldn't get the screws out. They'd unscrew a bit, then get stuck ('looping' back with each full rotation with a click, as though jumping the thread). I wonder if there's an issue there. – Z H Feb 6 '20 at 4:28
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No, it is not safe, because of potential shock hazard, possibility of fire and, as you correctly presume, equipment damage. For the time being, unplug the external HDD, if that's the only device causing the problem.

There are two likely causes for this issue:

  1. It could be due to power supply leakage issues, more likely the PS for the external HDD, rather than that of the PC, or the video jacks hitting the case. However, the only way to be sure is to measure the current from each device to the mains ground. A small amount of AC leakage is normal and acceptable, but the maximum current should be less than a few milliamperes (mA). The diagram below shows how to measure leakage current. Use caution! Touching a bad device could cause electrocution!

Measuring leakage current

   The 100 kilohm (kΩ) shunt resistor changes the AC voltage reading to AC current, with a reading of 1 volt (V) equal to 0.01 mA leakage. Connect one wire of the meter and the resistor to ground (e.g. the screw holding the outlet plate) and the other wires of each to the shell of the USB connector. If more than 30 or 40 volts show on the meter, the power supply is bad. If the power supply can be plugged into the wall outlet in different orientations (a non-polarized plug), test both ways, since leakage may be much more in one than the other.

   Check all devices with a USB connector, including the PC as well as the HDD. If the issue is the external HDD power supply, you can find a replacement PS and the HDD should be safe to use.

  1. It could be caused by ground loops, where a fault in AC power distribution causes the neutral or ground line of a wall socket to be above ground potential. This can be caused by miswiring of the outlet, a broken neutral or ground lead, or other fault. A simple way to check that is to plug all devices into one power strip , preferably one with fault detection (lights to indicate a bad ground or neutral or a burned-out MOV). If this solves the problem then the cause is household wiring, not the PC or its peripherals.
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  • Hey there, thanks for the reply! I should note that my externally powered USB speakers are also causing this issue when the plug touches the outside of my PC's USB ports, however I don't see any issues while it's plugged in. So it seems the issue is somewhere within the PC itself. I'm unable to source a multimeter at the moment - is there any way I can resolve the issue without one? – Z H Feb 3 '20 at 23:16
  • @ZH, If it's two different devices, then the PC's power supply is more likely to be the cause of the issue. See what I'm adding above on ground loops, though. – DrMoishe Pippik Feb 4 '20 at 1:15
  • Cheers for the extra info! I've tried two power board and two sockets, no luck yet. These two sockets are side by side though, so I assume they share some wiring. Further testing - I unplugged everything other than the Display Port monitor and tried touching the HDD and Speaker USB plugs to the sockets - same issue. I've tried using the second Display Port outlet on my video card - same issue. Tried plugging this monitor in via HDMI - no issue. Also no issue with my second screen, which connects via HDMI. – Z H Feb 6 '20 at 4:30
  • I noticed the issue occurring when I plug the power socket into my second monitor while the PC is on. There was a crackle from the 3-pin plug as it went in (typical of all computers I've worked with when wall socket is switched on) and as I did this the symptoms occurred again on the Display Port monitor. Opened up the case and tried unscrewing the motherboard to check everything's okay - and I found that I couldn't get the screws out. They'd unscrew a bit, then get stuck ('looping' back with each full rotation with a click, as though jumping the thread). I wonder if there's an issue there – Z H Feb 6 '20 at 4:30
  • Will open the machine up properly this weekend and try to get the motherboard out - I'm wondering if it's just incorrectly seated, has the wrong screws in it, or something similar causing something to short where it shouldn't. I'll also try a power socket down the other end of the apartment to see if that helps – Z H Feb 6 '20 at 4:31

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