ViewSonic VX2235wm and ADSL issues

I know this is a true story because it happened to me.

On a non robot slant I got to do some consumer electronics repairs recently. I have a 22" wide screen monitor on my main desktop, a ViewSonic VX2235wm. The desktop is five plus years old but still working well and more than enough of the odd internet cruising and mplab activities. The hard drive was starting to throw bad sectors so we decided to upgrade the machine to Windows 7 and replace the old hard drive. The wife installed Windows 7 fine. Everything was going along fine until we tried to access the internet. No joy. The Netgear ADSL wireless modem would drop it's internet connection whenever this desktop was on. Booting back to the XP setup, same issue. We also remembered the last time this desktop was on the laptop lost internet connection, but previously things had been fine.

We found that when the desktop goes on, 30 seconds later the internet connection gets dropped. Desktop goes off, internet come back. Wacky power issues?

Then I triggered it wasn't when the desktop came on, it was when the monitor came on. After replacing power cables things still weren't working. Different power circuits, still the same issue. We ran an extension lead from the 15Amp circuit in the shed, same issue. In all this time the monitor was working fine. The picture was fine, no odd behaviour.

Powering down the monitor and trawling the internet the wife found this monitor suffered from the common "bad capacitor" issue. Various electronics components get made with substandard capacitors which leak, fail, etc well before they are expected to. Based on what we were reading the wife suggested that I try and fix the monitor. At first I was reluctant to take apart a working monitor in case I made the issue worse and would be unable to fix it. However as the wife pointed out the monitor was useless as we lost the internet connection every time we turned it on. To the shed.

Taking apart the monitor was easier than expected. A few screw and then some gentle prying with a flat tip screw driver popped off the case. I didn't even break any of the snap together lugs. My daughter helped out by poking things with a screwdriver. A few more screws and the power supply circuit board was accessible. Three seconds later it was obvious what the issue was. The 400V 120uF capacitor had a nice blob of black goo coming out of it. Without that capacitor a large amount of electrical noise would be going back into the power line. This noise was so great it caused the ADSL modem to lose sync. Glad I've already had kids.

400V capacitors aren't stocked by the normal hobby electronics stores I go to like Jaycar, etc. Instead I went online to RS Components for the part, mainly as they were offering free shipping. $8 and a week and half later I had the replacement part. Out the old and in with the new. After putting the case back together I did a smoke test and the smoke stayed in. Taking the monitor back inside and turning it on, success! No more drop outs of the ADSL line. Happy days again. Now the wife can finish setting up the rebuilt desktop.

I can't see how electronic repair shops stay in business. For even a simple job like this the time cost alone would be the price of a new monitor. So next time you need a monitor check the skip bins. An hour, a soldering iron and some capaciors later you might have a working monitor.

Mini projects II

5 LEDs ready to shine

When you don't have time to do a real project you make up one. While doing some microcontroller tests I was using four separate LEDs. This was a bit messy with all the current limiting resistors. What would be better would be a small set of LEDs with resistors in one handy single block.

Ideally I wanted to use a SIL resistor array but didn't have anyone selling them locally (Little Bird Electronics now do). So it was going to be individual resistors and 3mm LEDs and some tight soldering. Also I wanted long header pins but no luck. Of course 3 days after I had finished Little Bird Electronics started selling long header pins.

My breadboard has two rows of holes above and below the normal breadboard area (ie for power rails). These power rail blocks have five hole groupings (instead of a continuous row of holes) so my LED stack would be five pins wide. That way I could plug in the block of LEDs into either the positive or ground rail depending on the circuit. As I am normally running 5 volts on my breadboard I used ?? resistors to limit the current to the LEDs.

The base for the project was a cut down piece of prototype board. Some tight soldering of header pins, LED, resistors and everything was done. I also had to file down the solder on the LED and resistor pins as the normal size header pins meant there wasn't much room underneath to ensure a good fit into the breadboard. Now the 5 bit loving can began.

Mini projects I

Prototype board chop shop

For the last couple of months I've been working on a large dollhouse for my daughter so work on electronics stuff has pretty much halted. However I did slip in a few quick mini projects. One was a test circuit for hobby servos.

On my long list of things to try is controlling servos with a microcontroller (via assembly language). Before I started that I wanted some way of testing the various servos I have. All are bargain bin buys or salvage so I didn't have a high degree of confidence in them working. I didn't want to be banging my head against the wall debugging assembly language when the issue was with the servo.

So I did a quick internet tour and found a simple servo control circuit based on the 555 chip. (http://sarconastic.tripod.com/servodriver.html) . The site had an excellent guide to the operation and troubleshooting of the circuit. Hats off to that.

I setup the circuit on my baby green breadboard first. Hooked up the first servo and success! Servo go up, servo go down. The daughter loved playing with it to the point that the pins on the 10K pot used were almost snapped off. I did have one servo fail as it only moved a few degrees and stopped. However after taking the servo apart I remembered many years ago I had modified this servo to do continuous rotation (ie not a server, just a gearhead motor really). The passage of time...

The breadboard was cramped and messy so I decided to do the project properly (and to be honest just wanted to do a little project so I feel like I'm making progress). Since the circuit was just a 555 chip and some associated components I used a small prototype board which I cut down to size to fit in the small project box I was going to use. I used molex connectors for the servo and power plugs to be attached to. I considered having the batteries inside the project box (using a 9V battery with a 7805 regulator) but decided that since this test box would get very little use having batteries slowed discharge and leak was a bit of a waste. Also the self tapping screws used in the project box would only strip out over time. So external power was the go. The only other external part was the 10K pot used to adjust the servo position.

To support the two molex connectors (a 3 pin for the servo, a 2 pin for power) I glued a scrap piece of prototype board to the underside of the lid of the project box. I used a step drill bit to drill out the hole for the 10k pot. An hour of soldering later everything was almost working well. The prototype board I had used under the molex connectors needed a bit of probing as the glue had meant the solder didn't connect to the molex pins very well. A bit more heat and solder solved that.

Again the self tapping screws of the project box were a pain. Soft, poor quality metal screw heads.