Category Archives: troubleshooting

Make VoIP work on your LAN

I have a client with a local area network with about forty client PCs. A few months ago, a third-party phone vendor added an Elastix “PBX” phone server, as well as a new workgroup router. Elastix provides a graphic administrator interface to its underlying Asterix telephone private branch exchange (PBX). Elastix and Asterix run on a Linux server.

The client has complained that phone callers’ voices have been randomly distorting, incoming calls randomly terminating, and after ringing, desktop phones’ handsets randomly die. The phone vendor assured my client that the new router (an Asus RT-N66U) was not at fault, and suspected that the problems were caused by cabling problems or configuration problems with the Elastix server.

After months of frustration, the client asked me to have a look. I began with the workgroup router. I noticed that it was configured to use cut-through switching. (Asus calls this “NAT Acceleration”, which sounds like a good thing, doesn’t it?  NAT is Network Address Translation. The router apparently defaults to cut-through switching mode.) VoIP (Voice over Internet Protocol) uses UDP (User Datagram Protocol), rather than TCP/IP. UDP is used for streaming real time audio and video because of its low overhead and potentially reduced latency. It does, though, require that its underlying transport mechanism be rock solid.

Cut-through switching does NOT provide a rock solid transport mechanism! Cut-through switching is fast, but it can damage frames and forward previously damaged frames. The more conservative store and forward method ensures that all frames that traverse a switch remain undamaged. It also will not forward damaged frames. Result?  A cleaner network.

Onion layer 1

Troubleshooting system problems is like peeling an onion. You remove one layer at a time and look for changes.

For our first layer, I reconfigured the workgroup router so that it employed store and forward, rather than cut-through switching. Then I waited for user reports. Users reported that we’d fixed the distortion problem, but calls occasionally dropped and/or weren’t initiated.

Onion layer 2

Next, I activated the workgroup router’s QOS (Quality Of Service) feature. I assigned highest priority to all traffic in and out of all active ports on the Elastix server. Then I waited. Users reported that all phones now work as they should.

Problem solved.

Think before adding boxes

Adding boxes to networks often works with little tweaking. Eventually, though, services begin to fail and users complain of slow response, as traffic jams the network’s pipes. Eventually, someone must reduce unnecessary traffic, and assign priorities to different classes of network traffic. I recommend doing this before problems occur — not after.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

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Restore phone orientation sensing

Last week, my Samsung Galaxy Light SGH-T399 phone with Android 4.2.2 stopped responding to orientation changes. When I rotated the phone from vertical (“portrait”) to horizontal (“landscape”), the display no longer rotated accordingly. In vain I clicked on the Screen rotation button.

sensor test screens markedupI feared that I’d physically broken the orientation sensor when I dropped the phone the previous day.  I loaded a rotation app, but found that it was a pain to use.  Eventually I discovered (thanks, Google) that by typing an odd sequence of keys, I could peek beneath the operating system and directly examine the data streams from the sensors. When I did this, the phone’s screen rotation function returned.

Here’s how:

  • Run the phone app, which displays the dial screen.
  • In sequence, press the *#0*# buttons on the dial screen.
  • A hardware test screen with 14 buttons should appear.
  • Tap the Sensor button
  • You’ll see the numeric outputs of the Accelerometer, Proximity, and Magnetic sensors
  • Press the IMAGE TEST and Graph buttons for the Accelerometer. The displays should respond to movement of the phone.
  • Cross your fingers
  • Restart phone

That did the trick for me. Your mileage may vary.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

I hate wireless keyboards and mice.

Microsoft wireless mouseToday, while troubleshooting a sick Windows PC, its wireless mouse stopped responding. Acck!

Luckily, I found a good ole wired Microsoft optical wheel mouse, plugged it into the PC’s USB connector, and continued on. I won’t waste time troubleshooting the wireless mouse.(Update: replacing both AA batteries brought the wireless mouse back to life.)

Computers are unreliable. I see no point in unnecessarily adding the complexity of wireless links between keyboards and mice. Complexity reduces reliability. (If you could see the technology within keyboards, mice, and their wired communications, you’d appreciate why it makes no sense to needlessly add the complexity of wireless links to these already complex interfaces.)

I’m sure that there are cases in which wireless keyboard and mice links make sense. I suppose that if the desktop is separated by a walkway from the PC, they’d make sense.

Other than that, the KISS (keep it simple, stupid) principle dictates wired keyboards and wired mice. Preserve precious local RF spectrum. And stop wasting AA batteries.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Assume nothing.

In the 1970s, I worked in west Africa on a variety of radio communication systems. One day I was told that the Nigerian Navy’s base in Calabar was unable to communicate with its ships at sea. Apparently their HF (high frequency, 2 to 30 MHz) kilowatt amplifier had failed. I was told nothing else about the problem.

Lack of detail was normal. Communication and travel then in most of Africa was difficult. I grabbed a Simpson 260 VOM (volt-ohm-milliammeter), a standing wave bridge, a small toolkit, service manuals, and headed to the airport. The 500 mile trip by air to Calabar went smoothly.

Nigerian Navy NNS Thunder
Nigerian Navy NNS Thunder
When I arrived at the Navy base, I was shown to the radio room, where new HF SSB (single sideband) transceivers and a kilowatt linear RF amplifier waited. The operators demonstrated low receive signal strengths and when they tried to transmit, the amplifier immediately turned off its output stage’s plate current high voltage power supply.

I removed the coaxial cable feedline from the final amplifier’s output connector and replaced it with a dummy load. The amplifier behaved normally. I measured the resistance to ground of the coaxial feedline’s center conductor; it was a few Ohms. This is not necessarily bad; antenna couplers and some antennas with a DC path to ground will display a low resistance to ground, but for most antennas, it indicates a problem with the feedline or antenna.

Check the simplest possible failure point first

I asked to see the antenna. We walked to a nearby field, and — guess what? The antenna was lying on the ground!

Problem solved, or at least we knew what was wrong. I wish that all problems were so easily solved.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

The Joy of Fix

Today I restored a neighbor’s mail program on his MacBook Pro. Both his IMAP and SMTP server name and port settings were incorrect. What had corrupted them? I don’t know. At least one “expert” had previously fiddled with this MacBook. After I restored its email function, the owner was elated.

It can feel delightful to fix systems and it was good to see the joy in my neighbor. Moreover, after solving server problems, it’s even better to see this joy in hundreds or thousands of users. It’s what keeps me in this biz.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

I nearly melted down my phone

While listening to a podcast on my Samsung mobile phone via the Tunein app, a pop-up announced, “Charging paused. Battery temperature too low or too high.” The pop-up remained on screen until I unplugged the charger. The battery had only about a 6% charge, so as soon as I unplugged the charger, another pop-up warned that the battery needed to be charged. Catch 22. Room temperature was probably about 77 degrees Fahrenheit.

imageI grabbed a cold pack from the freezer and rested the phone on its icy carcass. The over-temperature warnings ceased while I simultaneously listened to the podcast and charged the phone’s battery.

Decades ago, I helped develop military radio communication hardware. The products needed to pass environmental tests for vibration, shock, high and low ambient temperatures, and humidity — while under continuous full-load conditions. We invested many hours in heat management.

My mobile phone is clearly incapable of passing such tests. It’s intended for intermittent use — what’s known as low duty cycle usage. I’d guess that my phone can handle about a 10 to 15 percent duty cycle at full output.

This is probably as good as we can expect from consumer-grade products. We just need to have frigid cold packs ready if we want more.

My phone: Samsung SGH-T679. T-Mobile Insight II 4G.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Listen to podcasts when streaming fails

I listen to loads of pre-recorded and live podcasts on my Android phone. podcast icon headphonesMost are technical; others are about ideas, current events, science, and sports. Duration varies from a few minutes to a few hours. My go-to podcast listening app is Tunein. It works fine 9 times out of 10. Occasionally, though, I’m unable to stream the entire pre-recorded podcast file.

Usually the problem seems to reside with the podcast server, but sometimes the IP transport is at fault. Regardless, I then resort to plan B: I first download and save the mp3 file, then use the Winamp or VLC app to listen to the downloaded file. On my (2.3.4 Gingerbread) Android phone, both players are more flexible than Android’s built-in sound player. Winamp works well, but it may no longer be available.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

A quick fix for Android net connect problems

Airplane Mode screenshotOccasionally my Samsung Insight II phone (SGH-T679 running Android Gingerbread 2.3.6) quits communicating via IP with Internet hosts. Often, a wireless connection to a T-Mobile tower exists but there’s just no IP communication. Also, occasionally my phone insists that it can only establish a (low speed, perhaps 50 kbps) EDGE wireless connection to the tower; it refuses to connect at higher speeds (such as UMTS, HSDPA, or LTE).

A simple fix — short of shutting down and restarting the phone or system troubleshooting — is to temporarily place the phone in Airplane Mode (which shuts down its wireless radio transceivers) and then turn off its Airplane Mode (which starts its wireless radio transceivers). Your phone should connect to the cell site with the strongest signal — which may be different than the site that it was connected to before. Nine times out of ten this works for me.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Cloning Ubuntu drives

Last week I cloned a Xubuntu 12.04 system disk from an old IDE drive to a brand new drive. Acronis True Image reported that the process succeeded, but Xubuntu refused to boot from the new drive — the PC simply restarted without booting Xubuntu. I uttered a sound that you don’t want to hear from the guy who’s upgrading your system: “Uh-oh.”

Why it won’t boot
I learned in https://help.ubuntu.com/community/UsingUUID that Ubuntu relies upon disks’ uuid (Universally Unique Identity) numbers. Apparently Ubuntu first loads the Grub start menu. Grub reads /boot/grub/menu.lst, which uses the disk’s uuid number to define the disk on which the operating system to be booted is stored. Since the new disk’s uuid differs from the old disk’s uuid, we must edit /boot/grub/menu.lst.

A quick fix
Eventually I found a simple alternative to manual editing. The Lubuntu-based open-source Boot Repair CD repaired the problem with just one click. It takes a while to load but it’s a great little tool that claims to repair Windows boot problems as well. I’ve added it to my toolbox.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Xubuntu on Dell Dimension 4500

Last weekend a customer presented me with what he thought was a five-year old Dell Optiplex. It was actually a twelve year old Dimension 4500 with Microsoft Windows XP Home and was agonizingly slow. In any case, XP was rapidly approaching its end of life.

Dell Dimension 4500I feared that this PC was also at its end of life. Dell.com reported that it had shipped in 2002(!), and its hard drive SMART indicated over 50,000 power-on hours. Still, its CPU was a 2 GHz Pentium 4, so I decided to beat this dying horse a bit more before putting it out to pasture.

This desktop PC contained two 512 MB DDR memory modules. Both Dell and Crucial.com advised that this motherboard couldn’t address more than 1 GB of memory. Google revealed that in fact this motherboard could accept two 1 GB DDR memory modules, so I installed two 1 GB DDR memory modules, for a total of 2 GB. The BIOS reported 2048 MB total memory. Yesss!

image

Unfortunately the PC wouldn’t boot from a Xubuntu 12.04 live DVD. No wonder: this PC contained a CD-ROM drive, not a DVD drive. It also could not boot from a USB drive.

No problem. I booted from a Ubuntu minimal install CD, installed it, and used the sudo get-apk install xubuntu-desktop command to download hundreds of megabytes and install Xubuntu 13.10. (I don’t know how — or if it’s possible — to install anything but the newest release with the get-apk command.) It ran, but the display would occasionally blank and log me off. Not good.

I wanted to try Xubuntu 12.04, not 13.10, but how could I do this on a PC with only a CD-ROM — not a DVD — drive? I found a clever program called plop boot manager that installs on a boot CD-ROM, which in turn passes control to a boot thumbdrive in a USB connector. I created a plop CD-ROM and a Xubuntu 12.04 boot thumbdrive. It worked! Xubuntu 12.04 runs nicely on this old Dimension 4500.

Now I just need to replace its 50,000 hour hard drive. Maybe it’ll run for another twelve years.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Windows Update for XP

Within the last few months, Microsoft updated its Windows Update service so that to update Windows XP, the user must have Windows XP service pack 3 installed. Service packs 2 and 1 will not update via Windows Update. (I know — update of service packs 1 and 2 worked until recently, but Microsoft broke Windows Update. Maybe this is one way of encouraging XP users to update to Windows 7 or 8.)

windows update failure screen

Windows Update doesn’t report the cause of its refusal to work.

Older OEM setup CDs won’t allow Windows XP to update. I have a recent generic OEM Windows XP service pack 3 setup CD that works. You may be able to download just XP service pack 3 from http://www.microsoft.com/en-us/download/details.aspx?id=24, and then install service pack 3 locally.

Don’t ignore this problem. It’s critical that you keep Windows up to date.


Update, 10 Nov 2013:
This message thread contains a couple good ideas. It sounds like downloading a recent update agent does the trick: http://download.windowsupdate.com/WindowsUpdate/redist/standalone/7.4.7600.226/WindowsUpdateAgent30-x86.exe

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Recover a disappeared Windows partition

A client recently complained that his Windows XP computer had run slowly for weeks and now Windows wouldn’t start. Following power on, the Windows XP splash screen appeared for a few seconds, followed by a system reset. This sequence would repeat in an endless loop.

A low-level check of the disk revealed no bad sectors and Memtest86 revealed no bad cells. I used an Ubuntu (a Linux distro) boot CD-ROM; Ubuntu couldn’t see any partitions on the hard drive(!). This is not good news. I booted from a BartPE1 CD-ROM. It couldn’t see any partitions on the hard drive either. I booted from a Windows XP setup CD with a view to doing a repair install, but it could not see a Windows partition or system on the hard drive. Uh-oh.

BartPE screenshotThe cure for this sick pup? Boot from a BartPE CD-ROM, go to the command prompt, and enter the command CHKDSK C: /F. On this disk, chkdsk needed nine hours(!) to repair the NTFS partition and its table. At the 19% point during phase 1, the screen didn’t update for more than an hour. Several times, the PC seemed to have frozen. I was tempted to shutdown BartPE, but the PC’s drive activity light indicated that something was accessing the hard drive, so I allowed it to continue.

After nine hours, chkdsk reported that it had finished repairing the disk and exited to the DOS prompt. I rebooted the PC. Sure enough, Windows started and ran. A quick look revealed tbat the 160 GB disk had 0 (zero!) bytes free. This sick puppy needed more attention, but at least its data could now be salvaged.

I don’t need BartPE often, but when I need to access an NTFS partition and run a Windows or DOS command on a machine that can’t boot Windows, it’s just what the doctor ordered.


  1. BartPE (Bart’s Preinstalled Environment) is a lightweight variant of the 32-bit version of Microsoft Windows XP or Windows Server 2003, similar to Windows Preinstallation Environment, which can be run from a Live CD or Live USB drive. – from Wikipedia

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Be careful when cleaning

I recently replaced the hard drive in a three-year-old mini-tower PC that had spent its life on an office floor. It was a routine job with the expected dirt and dust inside the case. No vacuum was available, so I used the shop’s compressed air and blow gun to blow out the dirt, then reassembled everything. When I started the PC, it howled a loud screeching/ticking noise. I opened the case, removed power from the hard drive, powered on the PC, and listened with a stethoscope. The noise was coming from the power supply — probably its fan.

PC-Power-Supply-170wI removed the power supply, disassembled it, and discovered that the power supply fan’s 12 Volt DC supply wires — maybe 28 gauge, were rubbing against the spinning fan blades. A jet of compressed air through the power supply case perforations must have nudged the wires into the fan blades. I dressed the wires so that they were a quarter-inch from the blades, reassembled everything, and the PC worked quietly. Time lost to troubleshoot and repair this dumb problem which I had caused: 1 to 1.5 hours.

Moral:

  • Use a vacuum — not compressed air — to remove dirt from inside PCs.
  • Murphy’s Law applies even to routine jobs.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Create NTSC DVDs from PAL DVDs

Years ago, I authored a video DVD of European Group B Prototype rally car racing in PAL format. Last week I wanted to play it on a DVD player that reads only NTSC format DVDs. When I tried to play my video DVD, the player reported “Wrong Disk”. D’oh! I was stuck.

Just make an NTSC copy of your PAL video DVD
I found that I could use the PAL video DVD to create a new NTSC video DVD+R. I just renamed the PAL DVD’s VOB files to MPG, and used them as the source files for a new NTSC DVD+R. Here’s how:

Insert the PAL DVD in the DVD drive of a Windows PC. Copy the contents (files and folders) of the PAL DVD to a new folder on the PC’s hard drive, called, say, C:\DVDCOPY\. (The PAL DVD will contain folders named AUDIO_TS and VIDEO_TS.) In the folder named C:\DVDCOPY\VIDEO_TS, rename all of the files with .VOB filename extensions to .MPG filenames. You can do this within Windows Explorer, or, if you’re confident in DOS, try these commands:

Click the Start button
Click Run (if Windows 2000 or XP)
In the command box, enter CMD
A window with a black background should appear. Enter these commands (assuming that the PAL video DVD resides in drive D) :
>MD DVDCOPY
>CD DVDCOPY
>XCOPY D:\*.* /S /V
>CD VIDEO_TS
>REN *.VOB *.MPG

Run a video DVD authoring program such as TMPGEnc; tell it to read the .MPG files (in folder C:\DVDCOPY\VIDEO_TS) that you just renamed and create an NTSC format DVD+R. Continue within TMPGEnc as you normally would when authoring a video DVD.

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© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

A software problem masquerades as a hardware problem

I was asked to repair a Windows Vista computer that would consistently fail with a “blue screen of death” within minutes of starting. This is usually a symptom of a memory problem, but memtest86 (run from a DOS boot CD-ROM) failed to find a problem. Sometimes an overheated CPU will cause this problem, but the CPU seemed to be in firm thermal contact with its heatsink and both the CPU and power supply cooling fans were spinning. Sometimes a bad disk sector in the middle of the system kernel will cause this symptom, but testing the disk revealed no bad sectors. I suspected a weak power supply, but the computer ran fine with Windows in Safe Mode. I finally concluded that one or more 32-bit Windows drivers (which don’t load in Safe Mode) or anything else in Windows that doesn’t load in Safe Mode must be the culprit.

While in Safe Mode, I noticed that someone had installed a half-dozen unusual anti-malware and driver management utilities, plus a large assortment of toolbars. I tried to uninstall them, but most refused to uninstall in Safe Mode. Still in Safe Mode, I ran services.msc and disabled services that were associated with these dubious programs.

Interrupt Process
Source: Stephen Charles Thompson (anon_lynx)
When restarted, the computer ran fine. Those utilities must have been fighting over the same interrupt. So now it was just a matter of removing the superfluous junk that had been installed, updating Windows, and installing Microsoft Security Essentials.

What caused the problem?
When prompted to install a supposed piece of security software, novices often reason “If some is good, more must be better”. With security software, this is not true.


Caveat: Disabling the wrong service in services.msc can cause serious problems. Proceed with caution. Be prepared to reinstall Windows or at least to restore to an earlier restore point if something breaks.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695