Electrical Experts - How Can I Test A USB Device?

[Mr Milquetoast]

I’ve been having problems with my PC crashing and I believe the problem is a result of a Sitecom KV-011 USB KVM. This sounds unlikely so I’ve written a background of what has lead me to this conclusion. However, it’s a bit long so if you can probably skip to where I’ve put a line of dashes if you’re not interested in the background.

A little under 2 months ago I bought the Sitecom KVM. On the same day my brother came to visit and returned my graphics card which he’d borrowed along with Doom 3. While he was here we were looking at some graphical demos and videos and while watching them one of the graphical demos crashed and Media Player crashed while playing one of the videos.

Over the coming days applications continued to experience errors and I started asking my brother what he’d done to my graphics card. The errors became more frequent until eventually the system started restarting unexpectedly. This became a common occurrence, and started happening about once or sometimes twice a day.

At this point I decided find the source of the problem by trying the components of the unstable in my other PC in my working PC. At the time I thought the issue may be with the graphics card so I first tried a card from the other PC but the crashing issues remained. Furthermore the graphics card from the unstable PC did not cause any problems in the other PC, which ruled out any problems with that. I also tried switching the memory and power supply but neither of these was the problem. Next I switched the hard disks and did a clean Windows installation but the PC remained unstable. Finally I tried updating the BIOS to the latest version but this didn’t help.

This seemed to indicate that the problem was with the motherboard or CPU but since one system was an Athlon 64 and the other a Sempron I couldn’t switch the processor to test this. I resigned myself to buying a new processor but decided to put up with the crashing until the dual core Athlon 64s were released expecting it to lower the price of the single core chips.

Recently however the unthinkable happened and my second PC stopped working. It would not get passed the POST screen (which was a bit of a mess) and I couldn’t enter the setup screen. Even after clearing the CMOS the PC would not start or enter the setup screen. I plugged in a PS/2 keyboard in case it was a USB issue but it would still not enter the setup screen or get passed POST.

I swapped all the components over with the unstable PC just to try and get it to start up but even with different RAM, graphics card, PSU and hard disk it continued to do the exact same thing and would not start. I again assumed it was either the motherboard or processor but having never experienced such problems in the past could not believe I was having problems with both PCs. I should point out that no component in either PC is overclocked or operating in any way outside its intended use.

The only thing left was the Sitecom KVM which was plugged into the USB port each time I tried to start the PC since I never imagined it could cause such an issue. However after unplugging it and I turned on the PC and it booted up normally without any issues. At this point things quickly started to fit together and I realised the problems started the exact day I bought the KVM. If simply having it plugged in was sufficient to stop the PC starting then I’m sure it would be enough to cause the crashing on the other PC. It’s also the one thing I never thought to disconnect because you don’t think to disconnect your mouse and keyboard if your PC is crashing. The second has PC remained unstable since I stopped using the Sitecom KVM but at this time I’m assuming that the KVM has permanently damaged the motherboard.

The only noticeable issues I’d had with the Sitecom KVM was, frequently, when I press the button to change between PCs the mouse and keyboard would not work when it switched to the other PC. Sometimes I could simply unplug and reconnect the mouse from the KVM and it would work. Other times this would not work and if I switched back to the first PC the mouse and keyboard would not work on that either. Furthermore plugging the KVM into a different USB port would not help and I would eventually have the restart everything. At the time I just thought that this was an inconvenience but it may be indicative of a much greater flaw in the KVM.

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Since the problems with the second PC started the day I bought the Sitecom KVM and the other PC developed an issue where it would not even start up with the KVM connected it seems very likely that all the problems are a result of the KVM. However, I don’t want to start accusing anyone until I have proof so my question is how can I test if the Sitecom KVM is the cause of this?

One thing I’ve thought about is testing the voltage and amperage on the USB output from the KVM and seeing if it’s within the USB specification. Unfortunately I don’t really know how to do this or what range the voltage or amperage should be in. The other thing I considered was returning the motherboard to Abit in the hopes they could tell me what the cause of the problem is but I’d rather not do that just yet as I’d still have to confirm whether the CPU was working.

I’d be extremely grateful if anyone with electrical knowledge could tell me how I could go about testing if the Sitecom could have caused permanent damage to the PC.

Thanks a lot for any advice you can offer.

 

[zoobaby]

Well the spec on USB for Voltage is 5 Volts plus or minus 5%. There are 4 pins on a connector. On the host side, the flat connector, which the KVM should have, power and ground are the two outside pins. Hook a multimeter up there and you should see it. I doubt you will see anything wrong. Most devices look fine until they are under a load.

Checking current is a whole other mess. I reccommend skipping this.

Is the KVM powered by your PC or by a seperate supply? Try both configurations if possible.

Also, try playing with the USB legacy support in the BIOS. Enable it, test, disable it, test.

Best of luck.

 

[Mr Milquetoast]

Thanks a lot for your help. I'll have to get a multimeter on the weekend and give it a try. This evening I'll see what happens with USB support set to BIOS instead of OS.

The KVM is powered by an external +5V 2.1A power supply so presumably that couldn't go above 5V. Is it possible it could surge when switching between PCs?

Is there anything else that could be going wrong other than the power?

The fact that the problems one PC started up the day I got it and that the other PC yesterday would crash on the POST screen every time with the KVM connected but worked fine when I disconnected it does seem to indicate something is amiss with it an I'd really like to find the source of the problem..

 

[Mr Milquetoast]

I did experience something rather shocking when plugging it in. I as I plugged it in I touched the outside of the USB connector against the back plate of the PC case. When it made contact it produced a large amount of sparks as if I was using a mini welder. I quickly took it away but there was a burning smell left behind. This is something I’ve certainly never experienced before with a USB device, or anything else electrical for that matter.

I got a piece of metal and tried to recreate it but it wouldn’t happen. I touched it against the outside of the case again but it didn’t happen on that either.

Should something like that ever happen under any circumstances?

If it’s producing sparks like a mini welder I take it that would be enough to permanently damage the PC components?

When I couldn’t get it to do its welding act again I decided it would be safe to plug into the PC. I tried the KVM now with the power in and out and in all cases the PC would start up.

Sorry to keep asking these questions, but I’m growing more and more convinced that the KVM is what has broken the newer of my PCs and I’m not too happy about paying for the replacement components so if I’m rather enthusiastic to identify the cause of the problem. I’ve wasted hours and hours trying to find the cause of this issue and if it is the Sitecom KVM I’m not going to be happy with them to say the least.

Thanks again for your help.

 

[zoobaby]

I did experience something rather shocking when plugging it in. I as I plugged it in I touched the outside of the USB connector against the back plate of the PC case. When it made contact it produced a large amount of sparks as if I was using a mini welder. I quickly took it away but there was a burning smell left behind. This is something I’ve certainly never experienced before with a USB device, or anything else electrical for that matter.

Not good

Should something like that ever happen under any circumstances?

Not really, It is an ESD discharge. Static build up, but if sparks are as visable as you say, that is really dangerous.

If it’s producing sparks like a mini welder I take it that would be enough to permanently damage the PC components?

YES.

When I couldn’t get it to do its welding act again I decided it would be safe to plug into the PC. I tried the KVM now with the power in and out and in all cases the PC would start up.

Sorry to keep asking these questions, but I’m growing more and more convinced that the KVM is what has broken the newer of my PCs and I’m not too happy about paying for the replacement components so if I’m rather enthusiastic to identify the cause of the problem. I’ve wasted hours and hours trying to find the cause of this issue and if it is the Sitecom KVM I’m not going to be happy with them to say the least.

Thanks again for your help.

Man I would consider getting a new KVM. Hopefully no damage has been done. Best of luck and let me know how things go.

 

[Mr Milquetoast]

Thanks for the advice Zoobaby. I stopped using the KVM when I started suspecting it was the problem and switched the Windows Remote Desktop which is just as good, or better.

I think the KVM has already damaged one of the PCs. Over the weekend I'll try and film it doing its welding act and send it to Sitecom to see if they'll except responsibility. I'll just have to touch it against some metal every few hours to see if the charge has built up.

Thanks again for the advice.

 

[zoobaby]

Be careful man. If it is arcing that much, that could be some serious voltage. A static shock is usually under 50kV, closer to 10kV iirc, not a lot of visible arcing. If you are seeing it, then that is over 50kV and possibly some current. Current can kill, so be very careful if you do this or write it off if you can afford to and never buy their products again.

 

[Mr Milquetoast]

Yea it’s probably not the most sensible thing to be doing giving the sparks and smell it produced last time. If the KVM didn’t work I’d write it off but I don’t want to write off a fairly new PC.

Unfortunately I can’t actually get it to do the thing with the sparks again. I have actually unplugged and plugged in the USB cable on many occasions in the passed when I’ve been changing the ports to see if I could get the mouse and keyboard to work on the many occasions when I’ve switched over and it’s stopped working. It’s never actually done its welding act on any of these other occasions, so it must be fairly rare.

I’m convinced it’s the source of the problems but it looks like I will have a hard time proving it and I doubt Sitcom will except the blame unless I can get some sort of evidence. Oh well, I’ll keep trying.