Saturday, April 05, 2014

Samsung Chromebook slow to connect to wifi after bootup

I ran into an annoying issue with my Samsung Chromebook. The problem was that when I boot the machine from off (not just resume from standby), the wifi would take a longish time to connect to my wifi router, maybe about 30 seconds. This seemed to start after I began using my new router, a TP-Link TL-WR841N. The problem only affects my Chromebook, so I don't think it's the router's fault.

Eventually, I found this thread https://groups.google.com/forum/#!topic/chromebook-central/QhEsxhYXCKo via Google that hints at the solution. In this thread, one of the posters says that a router that supports 2.4 and 5 GHz may cause some delay because the Chomebook might connect to 2.4GHz first, and then reconnect at 5GHz.

My router was configured to support 802.11bgn, and 802.11n uses both 2.4 and 5GHz. I changed the router to use 802.11bg instead, and the Chromebook connect delay went away.

Tuesday, January 28, 2014

Samsung Chromebook vs HP Chromebook 11

Chromebooks

A few months ago, my wife got fed up with her old Ubuntu Thinkpad, so I bought her a Samsung Chromebook for $250 (it is only $230 as of Jan 2014). A few months later, our toddler spilled a large cup of tea directly onto the Samsung's keyboard. The next day it stopped working. A couple weeks later, we bought the HP Chromebook 11 for $280. This post describes our experiences with Chromebooks in general and compares the two Chromebooks that we have used.

Why Chromebook

Having spent much of my life maintaining the windows machines of friends and family, the idea of a machine that cannot be messed up by its user (even accidentally) is fantastic. We moved all our photos to Smugmug, so there was little reason to have a full computer for my wife anymore. In bullet form:

  • No manual patching
  • Instant boot up
  • No need for backups
  • Great battery life
  • Lightweight
  • The point about backups is really great when you need it. When our Samsung drowned in a pool of green tea, we didn't have to worry about it. No need to recover from a possibly dead disk. No need to reinstall software on the new machine. Just plug in the new machine and login. All the settings and applications we had installed on the old Chromebook automatically arrived in the new Chromebook.

    Drawbacks

    The CPU in the Samsung and HP is a bit slow; they both use the Samsung Exynos 5250 1.7GHz dual core. This processor gets the job done, for example netflix streaming is no problem, and web pages load up without much delay. The processor's weakness shows up when doing things like scrolling web pages quickly; the page does not re-draw frequently enough during the scroll, so the scrolling isn't smooth like my Macbook Pro.

    My wife needs Citrix XenApp to work from home. I haven't tried to install it on the Chromebook, but I have my doubts. For now she uses her old Ubuntu machine for working from home.

    Samsung Chromebook vs HP Chromebook 11

    Since the CPU and the OS are the same on both of these Chromebooks, the only real difference is the hardware, mainly the screen, trackpad, and case. There are some differences in the hardware ports, but those don't bother me much, and the keyboard is about the same.

    First the screen. The Chromebook screen is not great. I'm used to using a unibody Macbook Pro, so the TN screen in the Samsung is noticeably bad. Bad viewing angles and low contrast. However, it is a matte screen which I do like. The HP on the other hand is a fantastic (but glossy) IPS screen. It has rich color, great viewing angles, and a saturated look to it. This reason alone is to choose the HP even though it's $50 more.

    The trackpad on the HP seems a little better than the Samsung. It seemed like the Samsung isn't sensitive enough or something. The HP seems closer to the Macbook Pro's trackpad.

    The case on the Samsung flexes (and maybe creaks) when you pick it up or move the screen. The HP flexes much less and feels more solid.

    The Samsung was cheaper and came out earlier than the HP, so it's understandable that the HP is a better machine for just $50 more.

    Wish list

    The HP Chromebook 11 is a really great machine, but they could make it much better with a slightly faster processor and a larger screen with a correspondingly higher resolution. The HP Chromebook 14 had potential, but it has a TN screen with the same resolution as the HP 11, which is really unfortunate. I would gladly pay an extra $50 or so to have a nicer screen. The only real differentiator between all these chromebooks is really the screen now, so they would focus on using something nice. I think people will pay for it.

    Wednesday, January 01, 2014

    Repairing a HK42FZ007 Furnace Control Board

    PLEASE DO NOT ATTEMPT THIS IF DO NOT KNOW WHAT YOU'RE DOING. Your furnace control system is a critical safety system. If you repair or install it incorrectly or damage the system, it can burn your home down or cause a gas leak with people inside, causing severe injury and/or death. I cannot emphasize this enough. Be careful, PLEASE! The following information is for informational purposes only.

    For those people who would like to replace rather than repair their furnace board, I believe something like this should work: HK42FZ007.


    The non-condensing forced air gas furnace in our home had been having intermittent trouble starting up. The furnace brand seems to be "Night and Day" and the model is Plus 80. The normal startup sequence is something like this:

    1. Inducer fan starts
    2. Hot surface igniter glows
    3. Gas turns on
    4. House blower turns on
    The problem we had was the inducer fan in our furnace would cut in and out between step 1 and step 4. Most often, it would cut out right as the gas valve opened. This would correctly cause the inducer pressure switch to shutdown the furnace (the pressure switch is a safety mechanism). The problem here is that the inducer was cutting in and out; the inducer should not cut in and out if the thermostat is calling for heat.

    After doing some initial debugging and internet research, I learned that our furnace uses a Carrier HK42FZ007 Furnace Control Board. This board is similar to a number of control boards such as HK42FZ004, HK42FZ008, HK42FZ009, and HK42FZ011. From my internet research, it seems that all these boards except the newest HK42FZ011 have a design flaw that causes one or two of the power resistor solder points to crack, leading to an intermittent connection. The symptoms are intermitted inducer behavior much like what our furnace was doing.

    I pulled the board and took a peek. Here are some photos from this project:

    The control board inside the furnace, showing wires connection points.


    The control board inside the furnace, more wires.


    The control board inside the furnace, even more wires.


    To remove the board, there were two sheet metal screws holding the black case to the furnace. Make sure to record which wires go to which terminals before removing the board; I took detailed photos above.

    The control board is out of the furnace.


    Closeup of the control board box.


    Closeup of the control board box another angle.


    Back of the control board box.


    To remove the board from the case, gently pry the back off. There are clips all around the edge, and if you are careful, you can remove the back without damaging the case. Inside, you will find the circuit board:

    Circuit board front. Click for a larger version.


    Circuit board back. Click for a larger version.


    After some close inspection, I found cracks in the solder on R33 and R34, the large resistors in the board's cutout. Here's a closeup of the cracking. You can see the cracks on the two solder points on the left side of the image:

    Cracked solder on the left two solder points.


    To repair this problem, I used my soldering iron and reflowed the four solder points on those two resistors and added some more solder to the points also. Here's a photo of the repaired board. It's hard to see but the solder points are nice and solid now.

    Repaired solder cracks.


    I reinstalled the board and ran the control board's self-test. Everything seemed ok, so I fired up the furnace, and I have not heard the inducer hiccup for more than 6 hours now. I'm pretty certain the problem is fixed now.

    I hope this is helpful for people out there facing a similar problem.