Tuesday, September 01, 2015

Fixing a Kenmore Vacuum That Won't Turn Off

One day, after using my old Kenmore Canister Vacuum cleaner, its motor would not turn off, even though I flipped the switch to the off position. The only way to turn off the vacuum in this state is to pull the plug, which causes sparking at the outlet because the motor is a big inductor.

This vacuum has the on-off switch built into the hose handle so that it is easy to turn on and off. This vacuum is actually made by Panasonic, and has been super reliable for the 10+ years that it has been in my family. This repair guide should apply to many vacuums made by Panasonic, and other manufacturers.

After some debugging, I found that the problem is a high amperage relay inside the vacuum canister that welds itself together from repeated on-off cycles. This actually happened twice to our vacuum. The first time this happened in 2007, I replaced the relay with an Omron 25A contact / 120VAC coil relay that I found on Mouser; it fit perfectly, and is the relay pictured below. Unfortunately, Omron discontinued that model of relay, but I bet something like this relay on Amazon would work just fine if you use the normally-open terminals.

Eight years later in 2015, the relay got stuck again; this time I decided to service the relay instead of replace it. After opening up the relay, I confirmed that the contacts welded themselves together from repeatedly turning the vacuum on and off, which causes arcing and enough heat to eventually melt the contacts together.

To repair the relay, I used a screwdriver to pry the contacts apart, and then used sand paper to sand off the carbon build up on the contacts and to remove the melted bits of the contact. After the contacts were clean and shiny, I put the relay back together and tested it out. We've been using the vacuum for a few months since then, and the repair has been holding up. It might not hold up as long as a brand new relay, but it should hold up for a while, and I can just repair the relay again if it melts again.

Here are the steps for the repair:


Then, remove the hose from the canister:
Pull up on the HEPA filter cover to remove it and expose the case screws:
Remove the HEPA filter:
Remove the screws under the HEPA cover:
Open the bag compartment:
Remove the screws holding the blue case half to the grey case half:
Here's what you'll find inside the vacuum, the motor, the wire reel, and the relay (in my case, beside the motor):
Take a look at how the motor is oriented. You'll need to orient it the same way for the motor to fit into its spot:
Lift out the motor and move it aside, leaving the wires connected. You can now see the relay (the small box will all the wires connected to it):
Unscrew the relay:
Pop open both sides of the relay with something thin and small, like a small flat screw driver:
Slide the cover off:
Here's the contacts inside the relay. Noticed that the contacts are welded together. This is why the vacuum didn't turn off!
Here's the relay after separating the contacts:
Next, I sanded the contacts to remove the melted metal, and shine up the contact area:
At this point, I reassembled the vacuum which is the reverse of disassembly. The vacuum has been working great ever since!

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


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.


    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.

    Thursday, March 21, 2013

    Car Seats: Chicco Keyfit 30, Recaro ProRIDE, Radian RXT

    I guess I haven't posted to this blog in a long time. I had a kid about a year and a half ago, so that explains why. My sister was looking for a new car seat recently for her son who's heading towards two years old now, so I figured I'd review our car seats since we have three different ones now.

    The first car seat we had was this Chicco Keyfit 30. This one works for children less than 30 pounds and shorter than 30 inches, so this is for infants. We like this car seat a lot. The infant insert fits well when the passenger is very small. The harness's cam-buckle operation is very smooth, making it work well when you have a child that doesn't want to cooperate. The base clicks in easily to the seat also, and the base has a convenient bubble level and multiposition angle adjustment for leveling. The only drawback I can think of is that the seat + child is quite heavy, so carrying it is hard on the biceps. I don't know if other infant seats are lighter. We used this in a 1998 Camry sedan.

    The second car seat we bought is the Recaro Proride Convertible. This car seat is for bigger kids. You can't take this out of the car on a regular basis because it doesn't click into a base like an infant seat. This particular seat has a smooth action cam buckle also which I like. The straps are nice and flexible which is nice for maneuvering them around flailing baby arms. This car seat was hard to install though, mostly because it's so big and tall, but also because the seat belt path is an awkward position for our car. What's weird about this seat is that the seat base is super tall, but the actual seating position is quite small. When setup for rear facing, there isn't much legroom, and the seat is pretty narrow between the side bolsters for a larger child. The height makes it hard to fit in a car with low headroom, AND even if you have enough headroom, I ended up bumping (gently) our kid's head on the headliner quite a few times while getting him into the seat. This is our experience with it rear facing. We haven't tried front facing yet. We use it in a 2012 Honda Accord sedan with no sunroof which has a good amount of headroom for a sedan.

    The third car seat we bought is a Radian RXT. We bought this for use in a 2004 Volvo V70. This seat back is taller than the Recaro, and the seat is deeper meaning there's more legroom in a rear facing configuration. It folds up for transport (the reason we bought it), but it is also narrow so people are able to install 3 in a row in a smallish sedan. It seems like the seat is more comfortable in the rear facing configuration than the Recaro because there's more space. However, there are some drawbacks to this seat. Since the seat back is so tall, you need a lot of space to install it rear facing. In our Volvo, I think it would be difficult to install behind one of the front seats; instead, I put it in the middle position. The cam buckle is also more clunky; the action just isn't as smooth when tightening it. I often have to pull pretty hard to make it move just a bit, so now I don't loosen the cam buckle when taking our kid out of the seat. I only adjust the cam buckle when his clothes either make the straps too tight or too loose. Also the straps and shoulder pads are not as flexible as the Recaro.

    In summary, we like the Chicco a lot, but neither the Recaro nor the Radian is perfect (at least in rear facing mode). Maybe our opinions will change after switching to front facing.

    Friday, September 10, 2010

    How To Change the Struts and Strut Mounts on your 1998 Toyota Camry

    PLEASE DO NOT ATTEMPT THIS IF DO NOT KNOW WHAT YOU'RE DOING. Your car's suspension is a critical safety component. If you mess up, your car will become dangerous and deadly to you and everyone around you. The following information is for informational purposes only.

    This blog post describes how to replace the struts and strut mounts on a 1998 Toyota Camry yourself, but it should apply for Camrys from 1991 to 2001, and probably other models as well. This is not a difficult project, but it does take some time. It took me about half a day to do everything.

    To complete this project, you will need an assortment of sockets, wrenches, a breaker bar, a torque wrench, spring compressors, and an allen key.

    Struts generally go bad gradually, and at higher mileage. This car has 120k miles, and the struts were leaking oil. The strut mounts in this generation Camry are a known weak point. The symptoms of bad strut mounts are rattling over minor bumps, particular when the car is cold.

    I picked up the parts from autopartsarehouse.com. They have pretty good prices for the struts and the strut mounts; I got the KYB brand. The bellows didn't fit though, so I reused the old bellows.

    Section 1: Changing the front struts

    Step 1: This is the front strut assembly in the car.

    Step 2: Remove brake line, unclip ABS sensor wire clip, spray PBlaster on sway-bar endlink nut.

    Step 3: Undo the two strut-to-knuckle bolts.

    Step 4: Undo the sway-bar endlink nut with an allen key and wrench.

    Step 5: Undo the sway-bar endlink nut, done.

    Step 6: Undo the three nuts holding the strutmount to the strut tower.

    Step 7: Support the brake rotor/knuckle and remove the strut assembly from the car.

    Step 8: Close-up of the strut mount and spring seat.

    Step 9: Compress the spring with spring compressors.

    Step 10: Compress the spring with spring compressors, done.

    Step 11: Remove the top strut nut; be careful!

    Step 12: Remove the top strut nut; be careful!

    Step 13: Remove the strut mount.

    Step 14: Separate the strut parts: strut, bump stop, spring seat, spring, bellows, sprint seat.

    Step 15: Reassemble the strut assembly with the new strut and strut mount. Reinstall the top strut nut.

    Step 16: Make sure to use the correct strut since all 4 are different. Also make sure to orient the strut mount such that the arrow is pointing to the outside of the car.

    Step 17: Complete strut assembly with the new strut and strut mount.

    Step 18: Insert the strut back into the strut tower, and loosely thread on one of the three nuts to support the strut.

    Step 19: Complete strut assembly with the new strut and strut mount.

    Step 20: Line up the two strut-to-knuckle holes with a prybar or extension bar and insert the bolts.

    Step 21: Thread the nuts onto the strut-to-knuckle bolts, but do not tighten them yet.

    Step 22: Tighten the three strut mount nuts to the proper torque specification.

    Step 23: Reinstall the sway bar end link to the strut and tighten the nut.

    Step 24: Tighten the two strut-to-knuckle bolts to the proper torque specification.

    Step 25: Tighten the strut top nut to the proper torque specification.

    Section 2: Changing the rear struts

    Step 26: Rear strut overview, support the brake drum.

    Step 27: I don't remember the details here, but I believe you need to: 1) Fold the seats down, 2) Remove the interior panels on the c-pillars, 3) Tug forward on the rear package shelf to remove it.

    Step 28: Remove the seat belt tensioner.

    Step 29: Remove the bracket for the brake line.

    Step 30: Spray PBlaster on the sway bar end link, and remove the nut.

    Step 31: Spray PBlaster on the sway bar end link, and remove the nut, done.

    Step 32: Undo the two strut-to-knuckle nuts.

    Step 33: Undo the three nuts holding the strut mount to the body.

    Step 34: Remove the strut from the car.

    Step 35: Compress the string, and undo the top strut nut.

    Step 36: Disassemble the strut.

    Step 37: Reassemble the strut with the new strut and strut mount. Install the strut top nut.

    Step 38: Reassemble the strut with the new strut and strut mount. Install the strut top nut, done.

    Step 39: Like the front, hang the strut by one of the three mount nuts.

    Step 40: Reinstall the two strut-to-knuckle bolts, sway-bar end link, and brake line. Use the correct torque specifications.

    Step 41: Get an alignment!

    The alignment is critical to the car's handling and tire wear. After reinstalling the struts, you will lose the previous alignment because there is play in the two strut-to-knuckle bolts. Get an alignment right away or your car may handle funny and wear out its tires quickly.