IEEE Consultants' Network of Long Island

Oh, Yeah! - John Dunn, Consultant, Ambertec, P.E., P.C.

A few years ago, I received this set of circuit boards for first test. These were some boards! Each one had twenty some-odd layers and lots of components. Virtually nothing was working. I set out to discover why.

First I found a short circuit, then I found another and then another and so on and so on this went. The board was just riddled with short circuits all over the place. Although I'm describing this in a short (no pun intended) time, the whole process of discovery took quite a long while.

Finally, I went back to the draftsman who had done the layout work and got the reply " Oh, yeah! That happens sometimes." to which I stood there in slack jawed astonishment.

The Tree Lights - John Dunn, Consultant, Ambertec, P.E., P.C.

My father was an extremely intelligent man. Every week, he would fill in the entire Sunday New York Times crossword puzzle in one sitting of half an hour. That was when Will Weng was the puzzle editor and there were crossword clues like "Moldovan leader, 1929".

There were weaknesses though and we all have them, I guess.

We had never had electric lights on a Christmas tree, but one year, a neighbor offered to lend us a set.

Ohm's Law - John Dunn, Consultant, Ambertec, P.E., P.C.

There are times when one can really hit the proverbial brick wall because, as we all know, electrons are smarter than people.

You might have wanted to make some electrons to go "that" way in your circuit, but if they decide to go the "other" way, you're not going to fix that just by using your powers of oratory and persuasion. When a circuit isn't working the way it was supposed to and no amount of reason, logic, analysis or transcendental meditation seems to  be leading you to a solution to the problem, you do indeed have a problem.  

 

Finding A Circuit Board's Short Circuit - John Dunn, Consultant, Ambertec, P.E., P.C.

You have some circuit board with a short circuit in it somewhere and just to make life difficult a'la Murphy's Law, that short circuit involves a foil that carries current to a whole slew of destinations.

A method for finding exactly where such a short circuit is located is illustrated by the following real life example.     

 

Headset Driver Oscillations - John Dunn, Consultant, Ambertec, P.E., P.C.

In an investigation into parasitic oscillation of some headset driver amplifiers, the equivalent circuit of a nominally eight-ohm headset was empirically examined using mimicry. The method is shown in the sketch below:    

 

Your clock battery still matters - by Dave Rost

PC Problem:

On Tuesday, I turned on my computer and was sent to CMOS with a note about the clock. I found the clock a few hours off and an incorrect date. I fixed this and continued on my way with no further problems. I got the same complaint on Wednesday, but after fixing it, I got a complaint about a bad system disk, which certainly gets one’s attention. I stuck in my Windows XP emergency floppy and got a DOS prompt. I have two hard drives; one (“C”) has Windows and several partitions, the other (“D”) has my data in two partitions. A little changing of directory and directory checking revealed that the “C” and “D” drives had become reversed.

I got out my Acronis emergency disk and attempted to change the drive letters. They seemed to change as requested, but when I left Acronis, they reversed again. After several repeats of this, I opened up the computer case. Reseating the cables on the hard drives had no effect. After I unplugged the data disk, Windows loaded normally, and I was able to use my file management program (Ztree). All logical drives on the system disk were present. The data disk was not shown (as would be expected); the interesting thing is that there was no “D” drive; higher lettered drives were not re-lettered; there was a gap between “C” and “E”.