Wednesday, December 21, 2011

Note to self....

This is a photo of Lon Haldeman addressing the Oklahoma Bike Summit back in November. See the strong reflections in the shadows? Look carefully at the back of the gray shirt on the left and the black shirt of the guy in the center. This room was backlit by those curtains up front. Sunlight hit them and diffused through the room. This shot was one of the worst examples.

It disturbed me that the lens had this much internal reflection, but I didn't think it through until recently. I shot some neighbors Christmas decorations at night, and the reflection was so strong it appeared like a second set of lights! I tossed those shots away.

Light bounces around in a camera lens. Some passes through to the image sensor or film, but some small portion of it is reflected by all those glass surfaces. Most of them are coated to prevent this. That's the orange or blue stuff on the glass. Then it struck me - the UV filter I'm using isn't coated at all! In that test shot of a candle, a ghost image of the flames is hovering just above the top of the P.

Here's the same shot without the UV filter. Viola! No ghost image! Normally, I'd leave the filter in place because I can clean it with a handkerchief or even my t-shirt. I wouldn't do that to the front element of the lens. But I'll have to remember to remove the filter in those low-light situations or strong back light situations.

Learn from my mistakes!

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Friday, December 16, 2011

Route 66 railroad exhibit

Jordan and I were out doing some Christmas shopping earlier this week. We found some gifts for mom and daughter, but while we were out, I decided to stop to show him this old locomotive that had been quietly rusting away in the rail yard here in Owasso. It's being restored at a site west of Tulsa near Red Fork along with an old Pullman car, a tanker, and a caboose. Eventually the site will be a transportation museum.

It will take a lot of time and money to fully restore this Pullman. It was damaged when an adjoining car was set afire by vandals, and time has not been kind. This is the kitchen. It's roughly the size of my daughter's closet, big enough for two people to stand if they're careful with knives and elbows.

This was the dining area. Small tables and chaired lined either side, and that area at the back was the sun room. All the windows were broken by vandals. They're covered temporarily with plywood and high-impact plastic sheets. The volunteer workers said they'd found a cache of brass fittings for all the windows and doors, but as brass is so expensive they were reluctant to attach the hardware. It's certainly possible to reproduce that with a 3D printer, so that may be a better alternative.

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Wednesday, December 14, 2011

Golden oldie

I'm cleaning out my desk in the living room. In the bottom of a drawer under a pile of old tech manuals, I found a stack of cartoons from the Phantom Cartoonist!

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Tuesday, December 06, 2011

Circuit board detail

Here's something that has been giving me grief. I had a computer come into the shop on multiple occasions with related failures, most originating with the power supply. It would cycle power on and off rapidly, flashing the front panel lights just like a Christmas tree. Now, I'm OK with festive and all, but an aircraft computer isn't supposed to do festive.

Replacing the usual suspects didn't help. There are four big electrolytic capacitors on the power supply board, and they're usually responsible for these problems. I replaced the three easy ones, but the largest is a 1.1 farad capacitor (think BIG!) and it's held tightly by a large piece of foam tape. To remove it, I heat the board to 140F in an industrial oven, and then twist the cap off the board with a huge pair of Channelocks. It's a PITA.

But there's one other component that causes power supply cycling, and that's the pulse width modulator chip. In a nutshell, a computer power supply is closely regulated by the PWM chip. It compares the output voltage against a reference, and alters the current on the input to control the voltage on the output. It switches on and off at a rate just above audio frequencies.

The chip is more readily changed than that big capacitor, so I decided to do it first. Yes, I'm basically a lazy technician taking the path of least resistance. I cut two of the chip's eight leads - and the chip fell off the board! That's a photo of the board and pads up above. The solder didn't wet to the pads. Notice the dull copper that indicates some tarnish and corrosion.

I applied flux and tinned the pads before installing the new chip. In the morning, I'll investigate the surrounding circuitry for any loose connections similar to this one. Chances are, the board was contaminated when the chip was first installed. Nearby ones may be contaminated too.

This may seem a small thing, but finding and eliminating an intermittent is cause for celebration.