Thursday, February 20, 2014

Quick Decade Resistance Box Fix.

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I picked this Decade Resistance Box (AKA Resistor Substitution Box)up at the OSU sale many years ago, before I started trying to learn electronics. I dusted it off when I began assembling my “lab” but found that it was not particularly accurate, or rather grossly inaccurate.

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With all the resistors switched off it showed 34.3 kilohms  [there are three cases in which the final vowel of an SI prefix is commonly omitted: megohm (not megaohm), kilohm (not kiloohm), and hectare (not hectoare).] of resistance when it should show almost none.

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Yes, I cross-checked with another multimeter (VOM, DMM). All of my multimeters disagree. This is leading me to an obsession with standards and calibration which I will write about later this year.

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My favorite tool these days is DeOxit contact cleaner. There are lots of brands and types, this is what I have and use.


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So I sprayed the banana jacks.

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Then I disassembed the box and sprayed all the switches while actuating them to clean the contacts.

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Now it measures a very low .246 Ohms.

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I ran it through all the resistors and found that the 300 kilohm resistor read 30 kilohms.

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So I tested the resistors….

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Look at that, someone put a 30 kilohm resistor in by accident. I picked a pack of 300 kilohm resistors up at Norvac electronics after the hamfair this last weekend (interestingly enough there was a distinctive lack of pork products at the swap meet).

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While I was at it I replaced the banana jacks. The old ones were wobbly and the threads stripped out.

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Now it measures within the 1% of 300 kilohms. That’s my new-to-me Fluke 8840A multimeter from the hamfair.

Tuesday, February 04, 2014

Bad Toaster

I was having a toaster crisis.
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Our toaster (besides being upside down, a temporary condition) was more of a bread dryer, than a device which would actually make toast.

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The is the model number. It was cheap and I bought it a few years ago at Bi-Mart.

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When I tried to unscrew the bottom I sheared off one of the screw heads. It was screwed into soft plastic. I don’t know how you could even do that.

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I couldn’t find anything obvious wrong with it.

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You can see that some of the resistive heating wire is pulled away from the insulating/reflecting surface. I tried to pull it all away from the surface with a dental pick but there wasn’t enough slack.

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The only sections that glow are those proud of the surface. I’m guessing that the heat isn’t being reflected into the bread but absorbed by the insulation.

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Such that, if I put it on the highest setting,

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I get very dry and barely toasted toast with little evidence of the Maillard reaction.

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As a bonus it was pulling 4W all the time it was plugged in. That’s 12 cents a year!

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800W when one side is used.

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1550W when both sides are used. It’s supposed to be 1650W, but that’s probably within tolerances.

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Why not double check…

Anyway I decided to replace it. I spent some time researching and while you would think that the error was buying a cheap toaster, I replaced it with the Black & Decker TO1332SBD 4-Slice Toaster Oven, which was less expensive that the toaster it replaced, more versatile, and as a bonus? It actually will make toast. I’ve been quite happy with it for the past month.