Wifi for the Garage

A look inside the Linksys WRT54GS router used in this project.
A look inside the Linksys WRT54GS router used in this project.

Propagation has been abysmal, so it’s time to hang out in garage and work on projects. One catch: the garage PC gave up the ghost about a month ago. The Windows 7 computer had been functioning for a few months as a wifi repeater that let me use other wireless devices in the garage. Unfortunately, it looks like a power spike may have taken out the motherboard. I have retired that PC, and came up with a replacement: a linksys wrt54gs router reflashed with DD-WRT firmware and hardware modifications to add a cantenna.

Last week I made a video about putting up the hex beam, and now that I have the video editing software, I made one about the wifi repeater bridge project. Making video is somewhat addictive, so I think there are more on the way. I have a ways to go in terms of production quality – maybe Christmas will bring a better video-capable camera.

On the subject of videos, my home club, the Vienna Wireless Society, is now posting videos of presentations made at the club.

How my antenna switch became a loudspeaker

ad4I envision having a few antennas: the hexbeam, the G5RV, lindenblads for 70cm and 2 satellite work, perhaps a vertical of some sort if I can figure out where to place it, and maybe some kind of beam antenna for six meters. To make all that work, I’ll need some sort of way to bring the lines in the shack and to switch among them. I brought four alpha-delta four position switches, which should be enough to both perform this function and switch the lines to the available rigs. With that intention, I laid the switches on the bench and drew out the wiring diagram.

However, I never got there; not yet, at least. After piling up some connectors and coax and wood, I realized that what I really needed in the garage in order to do this sort of work was some kind of background noise to keep me entertained. So, I pushed the very useful antenna switching project to the side and turned back to the computer that I had fried a few weeks ago by plugging it into the 230V while its power supply was set to 110V.

Continue reading “How my antenna switch became a loudspeaker”

Fried Power Supply

The original fuse (white tube) after cutting away black heats hrink tubing.
The original fuse (white tube, bottom left) after cutting away black heatshrink tubing.

As a public service message, I feel obliged to share the following nugget of wisdom: before plugging a tower computer into a 220V outlet, reach around to the back of the computer and make sure the input voltage select is 220. Sounds simple, right? This isn’t something you have to think about for most laptops, which have dual voltage power supplies. They are happy plugged into either voltage and the power supply brick just works.

I’m not [arguably, perhaps] an idiot – I was aware of the switch. I just thought that the power outlet was off, but also I didn’t expect to encounter an issue until the computer itself was turned on. Wrong — ATX switching power supplies are always on. When I plugged the computer in 220V, there was a popping sound followed by smoke from the back of the unit. Never a good sign.

I pulled the power supply out, opened it up, and looked around. Nothing was obviously charred. My nose has lousy spatial resolution — it confirmed that something wasn’t right, but couldn’t help me localize the problem. I followed the wiring from the outlet inward. For a cheap supply, I was glad to see some decent capacitors on both live and return wires to ground, and across them. Also, some inductors to quell EMI. Next in line: the fuse. It had blended in because as a safety precaution, it was wrapped in heat-shrink. I cut away the heat shrink to reveal a white tube. I couldn’t see into the fuse, but my continuity tester showed it had blown. There was no fuse holder; the fuse was just soldered in by its leads, so I dutifully unsoldered it.

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The Laptop That Time Forgot. Almost.

Encouraged by my recent repair of the TS450 that had languished without computer control for a couple of years, I decided to reach back even further in the time stream and to pull my trusty Compaq nc6000 out of the vault. That laptop was my main computer for several years, starting in Sri Lanka right after the tsunami, then back to Bangladesh, a year in Virginia, and in Belgium up to 2008. In that year, it developed an annoyingly intermittent failure that slowly increased in frequency until the machine was unusable — it would just power itself off. It got to the point that it would turn off in only a few seconds, so my initial thought that it was heat-related didn’t hold up for long.

max1987I noticed that if I pushed on a specific place on the upper edge of the keyboard, just to the left of the fan, I could convince the computer to remain powered up for as long as I held pressure. I though it might be a bad motherboard edge connector or perhaps something to do with the fan itself, so I tightened down the fan. At the time, HP (which had recently acquired Compaq) was of no help, but over time, users consistently reported the same failure mode and kludgy solution. Finally, someone must have looked at the computer under a microscope and diagnosed that these failures related to microfractures in a single chip: the maxim 1987, a 48pin QFN chip that controls CPU power. If you google that chip, you’ll find scores of reports of its failure, either intrinsically or due to poor soldering connections. For my model, most of the speculation is that stiff hinges flexed the motherboard and caused mechanical failure, but I wonder if the failure is more related to repeated heating and cooling of the chip in operation.

The fix for this sort of thing is to resolder the chip, so that’s what I did. Unfortunately, the chip is on the underside of the motherboard, which is buried deep in the laptop. There’s nothing to do (aside from dremeling through the case) but to disassemble every module in the computer, completely remove the main board, flip it over, solder, and put it all back together. Torx screw drivers are not optional — there are a lot of torx screws of varying sizes, plus a few tiny philips head screws.

nc6000_splayed

I used a sparkfun hot air rework station 303D set to 385C and toasted the chip for 5-10 seconds per side. I could see that the solder melted as I did so, but had to take it on faith that the chip was sitting correctly and that all the connections were good (direct visualization is not possible).

In disassembling the laptop, when I removed the heat sink fins near the exhaust port, I found a cat-like fuzzy creature composed of many years of hair, link, fur, dust, and whatever else has been in the air that I breathe. I looked much worse than the air filter that they force you to inspect every time you take the car to JiffyLube. I did a general cleaning as I went through the computer, dusting out cooked ants, moth wings, and other animal life remnants. Since I didn’t want to cook the CPU, which is not far from the max1987, but on the other side of the board, I removed the heat sink and the chip itself while I was soldering. I cleaned off the chip, removing dry and questionably effective heat sink grease, and reapplying some of my own industrial grade heat sink compound.

I was surprised as anyone when the machine went back together with nary a left over screw. After five years out of action the LiON battery was dead flat, but I put in back in position anyhow. When I powered up, I got the bios splash screen followed by the Windows XP/SP2 screen. Windows did not fully load, but got to the point where the screen turned light blue and I got a usable mouse cursor. Program manager and task manager weren’t working, so I couldn’t get much further.

I suspected that the drive had been corrupted by erratic shutdowns, so I ran SpinRite from CD-ROM at level 2 and it detected and repaired some flawed sectors. On the next boot: success, 2008-style. I was staring at the same screen that I had used in 2008, now oddly dated looking. I fired up a few programs, and everything ran correctly. I was not, however, able to get the computer on my home network despite being able to physically activate the wifi module and to detect local networks.

IMG_20130620_002752I plugged the machine directly into my router and spent the next couple hours watching netflix (on my other computer), while windows update did its thing. Many were the times that I heard the windows boot sound. I enjoyed watching the patches of yesteryear strut their time across the stage: NET framework, Windows “Genuine Advantage”, and finally, the 800 pound gorilla: service pack three.

At the end of all this, I found that my home wifi didn’t work, but I could connect to an open network, so it was a problem with encryption. I realized that WPA2 wasn’t out when the machine was manufactured, and that my home router would not roll to a lower standard. I was pleased that the Intel wifi card was supported by an update that came out in 2009, and which enabled it to connect to modern wireless access points with good security.

So, the nc6000 seems to have made a full recovery. I’ve promoted it to “back up logging computer” for the station, which is great timing, since I now have two computer-controllable radios. A new battery (a bit less than $40) has been ordered, and will complete the update.