Tom Moertel's Weblog: Tag hardware

Repairing my Kenwood A/V receiver's remote-control sensor

Tom Moertel — Fri, 25 May 2007 17:42:00 -0400

The Kenwood audio-video receiver that forms the core of my home theater system stopped responding to its remote control. As I discovered shortly thereafter, having to leave the couch to fiddle with knobs degrades the “home theater experience.” Clearly, something had to be done.

I knew the receiver was the culprit because the remote control worked fine with other components of my system. I figured the IR sensor had gone bad and did a little Googling for “Kenwood” and “IR sensor” and “problem”. The results revealed that many other Kenwood customers had the same problem.

The cause of the problem, I learned, was that the solder joints which connect the IR sensor’s leads to the display board eventually fail because of thermal expansion. That explanation seemed to account for what I was observing, so I cracked the case in search of visual confirmation.

First, I found the joints where the IR sensor was connected to the circuit board. The vertical red line shows where I found them:

Then I examined the joints closely. Sure enough, at least one had completely failed:

The problem confirmed, I moved to the solution phase of the project. With my soldering iron, I touched-up the joints:

It wasn’t my best work, but it did the job.

Now my receiver is back on speaking terms with its remote control, and I have returned to the modern world. Life is good

How to make sure your servers come back up after an extended power outage

Tom Moertel — Wed, 09 Aug 2006 00:35:00 -0400

If an extended power outage drains your UPS, and your servers are forced to shut down, will they automatically start up again when the power is eventually restored? It’s a good question, especially if your servers are in some distant, unattended server room. Unless you’ve tested your servers, don’t assume that the answer is Yes.

Many servers offer a BIOS configuration option that forces them to automatically power on when they receive line voltage. If your servers have this option, just set it and you’re done.

Unfortunately, some servers, including a Dell PowerEdge 1600SC that I’m using, lack this configuration option. When these servers turn themselves off as the final step of a UPS-controlled shutdown, they don’t start up again when the power is restored. Because they were shut down before the power was cut off, they think they are supposed to remain off when the power is restored. That is, they remember their on/off status across power outages.

Fortunately, there is a way to make sure these servers automatically power on: shut them down without powering them off; halt them instead. That way, when the UPS finally cuts off the supply voltage, the servers will still be in their “on” state, and they will remember this state across the outage. Later, when the power is restored, the servers will automatically restore their pre-outage state and power up.

With Fedora Core Linux and Network UPS Tools, it’s not difficult to make sure the servers are halted instead of powered off, but the implementation isn’t obvious. To spare you the digging, here are the important bits.

When the power fails and the UPS-monitoring software decides that the batteries are almost depleted, it will initiate a server shutdown using the command defined in the /etc/ups/upsmon.conf file. The default command is this:
```
SHUTDOWNCMD "/sbin/shutdown -h +0" 
```
The shutdown command will tell the init process to enter runlevel 0, which is the prepare-to-halt-the-system runlevel.
The init process will stop all of the running services in an orderly fashion, and then, as the last step, invoke the final script in the shutdown process: /etc/rc.d/rc0.d/S01halt.
The final lines of the S01halt script will power off the server. Unless, that is, the file /halt is present, in which case the script will halt the server instead.

Thus the trick is to make sure that the /halt file does exist. The trick turns out to be easy to pull off; just redefine the shutdown command in /etc/ups/upsmon.conf:

SHUTDOWNCMD "/bin/touch /halt; /sbin/shutdown -h +0"

And that’s all there is to it!

Replacing the fan array in my HP ProCurve 4000M switch

Tom Moertel — Fri, 11 Nov 2005 21:42:00 -0500

The main network switch in my home office is an HP ProCurve 4000m, which has been running non-stop for over half a decade. It is a great switch, and even though it is getting old, it is still dependable.

A while ago I noticed that the 4000m’s fault indicator was lit. So I logged into the switch and checked the log: fan 1 was dead. The switch has built-in redundancy (three fans), and so I didn’t worry about it, but I did call HP ProCurve tech support.

The woman I spoke with was friendly and helpful. I told her what was wrong, and she said a new fan array would be on my doorstep within 48 hours. No charge. (I guess the ProCurve warranty really is worth something.)

Today, I installed the array. This meant opening up the switch, which is a fun thing to do. If you are curious about what is inside of a 4000m, I took photos of the operation.

During the process, I recalled why I love old-style HP engineering:

The replacement parts came with clear instructions that showed me how to remove the old array and install the new one. They were easy to follow and didn’t leave anything to guess.
The 4000m is solid – inside and out.
The electrical components are top quality.
The industrial engineering is superb. For example, all of the user-removable screws have non-stripping torx heads and are designed not to fall out and get lost; instead they remain attached to the module or panel you are removing. (See this photo of removed modules to see how the screws stay in place.)

Everything about the process made me think, wow, this is really well engineered.

The thing is, I know, as I sit here and watch the blinking LEDs on my now-restored 4000m, that my next network switch will probably be a Dell.

As much as I love the ProCurve engineering, the Dell price is compelling. Even if I expect the Dells to fail twice as often (and the Dell warranties are comparatively lame), I can buy twice as many Dells and keep spares on the shelf – and still save money compared to the equivalent ProCurve equipment.

I find the situation somewhat sad. I am an engineering guy to the core. So when I go for the cheaper product because it is so darn cheap, I know that much of the market will do likewise. That bodes ill for HP. Like HP’s calculators, the ProCurves too may pass into history.