Question Front panel USBs can cause odd monitor artifacts, should I be concerned?

[Tatami Temple]

Apologies if this thread doesn't end up in the right place.

This is on a new build. When I go to plug in a USB plug that's powered to one of the front panel ports, if it touches the port in a certain way it causes one of my monitors (HDMI) to flicker green for a split second (this also shows up in the same brief flash when the computer shuts down, if relevant). Nothing happens if it's not a powered USB plug, and this doesn't happen with the back panel USBs, just the front ones. I can't imagine why or how only the front panel USB would be affecting the monitor for some reason.

I was a bit concerned about it at first, but then I just had a SD card that was plugged into one of the front USBs via an adapter end up corrupted after being unplugged (I always make sure to use the safely remove device feature), which makes me worried this isn't some innocuous coincidence, and these ports are a danger to any device I dare connect to them. I really don't need this thing nuking anything more important if that's what it's trying to do.

I've checked all the connections and wires for anything that might be making contact that shouldn't be but nothing appears wrong, and I've already swapped out the entire motherboard for an unrelated reason. The only things I can think of is maybe the case's front panel might be poorly wired (Lian Li Lancool 205M, just for extra information), or maybe even the PSU (EVGA Supernova 650 G5) is defective in some fashion, but I don't know how I'd be able to verify since I do not have spare ones to test with.

Any suggestions or reasons why this could be happening would be appreciated.

 

[Misgar]

If the USB3 cable from the mobo up to the front panel plus the cable from the front panel to the external device exceed 2ft (60cm) you may have problems due to crosstalk (and volt drop on powered devices). Keep your cables as short as possible or use the rear ports.

 

[scout_03]

ir most likely seams that usb connector might be making a short on case side front panel or inside it also made shure no cable from it touch the case .

 

[Misgar]

When you say the USB plug is "powered" does that mean you are feeding +5V from a mains power supply into the computer (not a good idea) or are you saying the device at the other end of the USB plug receives power from the computer.

 

[Tatami Temple]

I'm not sure it's an option to swap out the USB 3 cable, but I don't think it's long enough to cause problems, since it doesn't have much slack left once it reaches its destination.

I tried to redo my cable organization multiple times, but no dice on that fixing it either. I did my best to make sure the USB 3 wasn't touching any of the panels.

By a powered USB I mean like an external drive that is getting power from an AC adapter. It happens regardless of which USB cable and external drive is used, just to rule those out too.

 

[Misgar]

If you have a multimeter, set it to the 20V AC range and connect one probe to the metal shell of the external drive's USB plug and the other probe to the metal chassis of the computer. If the meter indicates a voltage difference, you may have found the problem.

To explain. Some mains power bricks have only two connections to the mains, i.e. Line and Neutral, but no Earth. This design is quite safe because it employs "double isolation" between the high voltage mains supply and the low voltage SELV supply.

However, in rare occasions, the Class-X and Class-Y EMI/RFI suppression capacitors in the PSU allow a small AC leakage path through to the DC output. When you ground the USB connector to the chassis of the computer, a small AC current flows which might explain the glitch on the monitor. Ideally you should change the DC PSU.

As for USB3 cables for external drives, I use 1ft/30cm leads for USB-A and 8in/20cm leads for USB-C to reduce potential data corruption. If you're using much longer poor quality cables, you may not get perfect data transfers, especially when using the front panel ports. That's why connecting to the rear panel is preferred.

 

[Tatami Temple]

I'll probably just have to accept non-functioning front ports for the foreseeable future unfortunately since I have no way to properly diagnose it. Disappointing but better than the thought I might be risking damage to anything I connect to it.

Though, should I still be concerned about the green flash on the HDMI connected monitor when I shut down the computer, or is that nothing to worry about? It doesn't happen to the other monitor connected via DisplayPort for whatever reason.

 

[Misgar]

Have you tried changing the PSU for the external drive yet, or checked for a voltage differential between the two devices?

I wouldn't be concerned about the green flash. The sun does it when it sinks below the horizon sometimes.

 

[Tatami Temple]

I don't have access to a multimeter to test voltages sadly.

However, I did swap the AC adapter for the external drive (checked the input/output just to make sure it was identical), and it doesn't do the screen corruption when I touch the USB from the drive to the front panel USB ports. I swapped around just to make sure, and it's just the old AC adapter I've been using. I guess something's wrong with it, for how long and what exactly I'm not sure. I feel a bit stupid for overlooking such a simple possibility, I was hyper focusing cause of the SD card corrupting. The card is only a year and a half old after all, I know they can be unreliable but it still seemed short for it to blow up so I'll probably be a bit antsy for a while.

Regardless I suppose that's solved, I still would like to know what the monitor's issue is too, but if it's not indicative of anything bad I can rest about it. Thanks for the assistance.

 

[Misgar]

By the sounds of it, your old PSU had "leaky" EMI/RFI capacitors as I explained earlier. Good to know the new PSU has fixed the problem.

Cheap PSUs and battery chargers use questionable designs, fewer components and sub-standard construction methods, when compared with high quality designs.

There is a reason why Canon and Nikon et al charge $50 to $100 for their camera battery chargers, but Chinese copies cost $10 to $15. If you open up the chargers, the difference is considerable.

If you ever want to check an SD card (or similar) for corruption, download a copy of h2testw.exe, created by a German software writer. Its main use is to detect fake memory cards, purchased for suspiciously low prices on AliExpress, eBay and Amazon.

H2testw writes 1GB test files to the card until it is full, reads them back to see if they're OK, then checks if the claimed capacity matches the total number of GB written.

Fake Sandisk and Samsung cards claiming to be 64GB often contain a 2GB memory chip, but are "fixed" so they appear to be 64GB. When your camera has written 2GB to the card, additional file write operations silently delete older files.

The first you know about it is when you cannot find older photos you saved 3 months ago, because they've been overwritten by newer shots.

Old CRT monitors and TVs used to flash when switched off. Who knows what signals are sent to your display when you switch off the computer. Don't worry about the green flash.