For our small band of loyal blog readers, we start with a mystery, a final exam and a real-world electronics problem. These all have an element of troubleshooting.
The mystery which may have come from a logic class is as follows. A man goes into a bar and asks for a glass of water. The bar keep reaches underneath the bar and pulls out a gun which he points at the man's head. A short interlude and the barkeep smiles, the man says Thank You and walks out of the bar.
So, what just happened? Pause! The man going into the bar had hiccups and with the action of the barkeep -- the man was frightened and the hiccups stopped. Thus, the smile and Thank You. A stretch and something in a thousand years you would never have guessed but plausible. At times troubleshooting a problem is the same -- think subthreshold conduction.
Next, we turn to a final exam question. The course was Short Story Creative Writing. The question was: Create a short story that has three elements including a mystery, sex and religion. A really hot YL spends about three minutes writing and turns in her paper. The professor had a look of dismay and said aren't you even going to try to do the test. She says: I'm done. The professor reads her work and beams a huge smile and marks an A on the work. It was but one sentence which read as follows. Oh my God, I am pregnant, and I don't know who the father is! She had the three elements, it was spare, creative and left the reader engaged and wondering.
When we trouble shoot a problem quite often it is a simple issue that is not so obvious. You can make contacts with a one transistor Michigan Mighty Mite and get signal reports just like from a FLEX 6700. Fixing a M^3 can be less onerous than popping the lid on that FLEX box.
The IRF510 Final!
For the one or two nitpicker blog readers who are always looking for errors, one of the resistors is not marked -- it is in yellow so that will make your task easier to find the nit. Its value is not the problem. So, this circuit was built, using all new parts including some surface mount parts.
When fired up the output was almost nil. I rechecked the wiring, insured the bias was hot and set for about 3.5VDC. There was 12VDC on the Drain. I looked for solder splash or whisker shorts and all solder connections seemed solid.
I had about 5 volts of RF at the input side yet hardly any output. So, what is wrong? Oh, the thumb on the IRF510 was cool to the touch.
Fault tree analysis kicked in to overdrive. While there was RF into the stage, there was hardly any output following the 10nF input cap. This cap was an 805 SMD rated at 25 volts. The issue was I applied too much heat in the soldering process, and it was "open". I replaced it with a ceramic unit and boom full output. Troubleshooting took more than 5 minutes, but the open cap was not so obvious at the outset but revealed as a part of going through the usual suspects list.
When we troubleshoot a problem, it helps to noodle through a list of the usual suspects such as bad parts, improper wiring or wrong value parts. Is there power to all parts of the circuit and how about shorts or as in this case open circuits. This is a fault tree analysis.
TYGNYBNT. Don't eat your pets.
73's
Pete N6QW
