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USB devices keep dropping out

By viper150
Feb 12, 2013
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  1. I recently purchased a new computer for my business. It is a Systemax SYX-1113 operating on Windows 7. I operate three small CNC controlled machines with it. The machine input is via serial cable which I have connected to the computer with USB to serial adapters. I have operated these machines in the same configuration with older pc's that had far less power than this one without any issues but this one keeps dropping the usb connection. The computer is plugged into a 15amp circuit that has nothing else operating on it other than the monitor and speaker system. I have checked and tested the circuit for wiring issues, circuit breaker issues and power draw which have shown no problems with the circuit. The problem begins when I use a small paper shredder connected to the same a/c circuit. I can hear the usb connection drop by the familiar usb disconnect sound and the connection to one or more machines is lost when the shredder is operating. When I unplug each of the usb adapters from the computer I get another disconnect sound and then plug them back in. The connection is restored and I can communicate with the machines once again. There is not a single adapter that fails or a single usb port. I have tried every combination of usb ports available on the computer with the same results. No other devices fail that I can tell such as keyboard, mouse or printer. They all appear to remain connected unless they are re-setting themselves. A couple of days ago I added a small refrigerator to the circuit and now it appears that when the fridge compressor kicks in the usb connections drop as with the shredder. Do I have a problem with the computer power supply that will not deliver enough power for the usb ports or could there be a loose connection or board? The specifications show that is has a "550 watt Bronze Power Supply". As I stated before, I have had the same CNC machines connected with the same usb-serial adapters as well as two dongle security keys, keyboard, mouse and printer connected to other less powerful computers and never had any issues like this. Am I asking too much from the usb power supply or something? It has twelve 2.0 ports and two 3.0 ports available which I have tried all of them with the same results. I am using seven ports to include two for the dongle keys which I can't imagine would draw any noticeable power. I am not a computer genius so if this is something simple that is easily solved someone please let me know how to do it. If not I guess I'll have to have a little talksee with the salesman that sold it to me.
  2. SNGX1275

    SNGX1275 TS Forces Special Posts: 12,532   +301

    I'm not an expert on this, so perhaps wait for someone else's thoughts before doing anything. But I can tell you what I think is happening and what I would do.

    I think that the compressor kicking on/shredder motor are generating some electrical noise on that circuit and your Power Supply Unit (PSU) is unable to properly handle the noise. That is a little disconcerting in itself.. but on top of that USB is 5V and hard drives also use 5V this makes me concerned about what that noise and/or voltage drop/spike is doing to the hard drive PCB.

    What I would do, is plug your computer in to an Uninterruptable Power Supply (UPS), they are supposed to kick in if an undervoltage, overvoltage, or significant electrical noise is encountered. That should solve your problem. However, it is going to be somewhere around $50 or more (you can get cheaper ones, but I think the minimum that should be purchased is one that will interface with your computer, the real cheap ones won't). You can have your shredder and fridge on the same circuit still, but I would advise against plugging those devices into the UPS itself. The UPS will likely have 1 line of outlets that are not on the 'battery backup' side, and they obviously should be isolated from each other, but I would feel more comfortable if your fridge and shredder were not plugged in to the UPS unit at all.

    So, if you can talk to your salesman, I would suggest to him that you think you need a better quality PSU. If he's going to charge you more for a better one (which he probably will), keep in mind that if the increase in price is more than the price of a UPS it probably isn't worth it.
  3. viper150

    viper150 TS Rookie Topic Starter Posts: 17

    Thanks SNG. I have tried to determine whether it is a computer issue or a/c issue. I am more qualified as an electrician than a computer engineer and have tested the line voltage and amp draw and have found no voltage drops or fluctuations. I physically checked every outlet in the circuit for loose or corroded wiring or any other problems and found none. There are only four outlets on the circuit and I am using only one which is for the computer and related devices. I am reasonably confident that the a/c circuit is not at fault here. I moved the fridge to a new location and circuit yesterday and haven't had any issues so far. I am convinced that the problem is in the computer and wonder if the psu is substandard or faulty. I may want to use other outlets in the circuit in the future and need to find out what is wrong with the computer. As I stated, other computers have operated the same devices on the same a/c circuit without any issues. As far as your suggestion of adding a ups, I should have done that long ago but get busy and forget about it. We have many short power interuptions during summer storms and I should have had one installed a long time ago. Thanks for reminding me.
  4. Dat1Gamer

    Dat1Gamer TS Booster Posts: 135

    Im not a pc expert but it almost sounds like its a faulty PSU


    EDIT: Also PSU's have to draw 3-5Aa to work properly from my experience with Thermaltake PSU's
  5. SNGX1275

    SNGX1275 TS Forces Special Posts: 12,532   +301

    Noise should average itself out so the voltage would still look reasonable right? To find noise I think you'd need an oscilloscope. So I'm not surprised you aren't seeing any problematic voltage drops.

    I agree, the a/c circuit is probably in good order as 15 amp should be fine, possible exception would be compressor motor, shredder motor, and computer startup all at once, and even then....

    I think it is the PSU as well. I know from experience with CRT monitors and paper shredders that the monitor can/will go squirrely if the shredder is running on the same circuit. That is why I made the guess that it was electrical noise and that the PSU is passing that on in some way (would have expected the AC to DC conversion to handle that..) down the 5V rail(s) to the USB devices. This shouldn't happen, so it does seem like a faulty PSU.

    Speedfan and whatever Everest is calling itself now are software programs that can monitor voltages from the PSU. Might be interesting to see what they say is happening. Sampling rates may not be high enough to catch anything interesting though. Not that you could do anything software wise to change the voltage behavior, but might be something fun to have for you anyway.

    I suggested the UPS because I didn't know your situation, and maybe if you could borrow one to put in line you could see if that takes care of the problem. Its a hell of a lot easier than replacing the PSU, but replacing the PSU isn't that big of a deal anyway.


    So... In summary, yep, if you can get the PSU replaced that sounds like the way to go. I suspect a UPS will fix the issue too, but it is really like medicine for the problem rather than just fixing the problem. I do think it is important to fix or medicate this soon though because whatever is causing the USB to drop out sounds almost certainly electrical related. For USB this is going to involve +5V and a ground. +5V is used on hard drives too, and ground is used by everything. So even though the problem may appear to only affect USB, the cause is likely having some effect on at least the hard drives and potentially everything.

    Good luck.
    Dat1Gamer likes this.


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