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  1. hevans1944

    AC adapter not working, strong burning smell

    You are probably referring to the transformer steel laminations, around which the primary and secondary windings are placed (on plastic bobbins). You do NOT "open the box-like metal portion that you see in the photos." To troubleshoot this and determine if it is repairable, you should remove...
  2. hevans1944

    What's so special about mini-MELF 1N914s?

    Trump will make them an offer. They not refuse. OTOH, you can get a pretty good deal on surface mount 1N914 diodes if you aren't too picky about specs. See here.
  3. hevans1944

    Amplifier Potentiometer Replacement

    Below is a close-up image of the OUTPUT POWER controls. These are allegedly two 12-position detented controls, yet the markings on the panel only show eleven detent positions, namely: 1W, o, 5W, o, 25W, o, 50W, o, 90 W, o, and 120W. The detent positions with dots, intermediate between the...
  4. hevans1944

    Amplifier Potentiometer Replacement

    Did anyone notice that the (almost illegible) schematic shows two mechanically ganged pots on a common shaft? Well, that's how I interpret the dashed lines from one wiper to the the other wiper. Your mileage (or kilometers) may differ.
  5. hevans1944

    Negative Voltage

    Voltage is always measured between two points. Think of a common dry-cell where one end is positive and the other end is negative. A typical alkaline cell produces 1.5 volts between its terminals. Whether you consider that voltage to be positive or negative, depends on where you decide to...
  6. hevans1944

    DCC to Arduino adaptor board

    Space saving is the main reason. I recall, about the middle of the last century, opening up the case of a Japanese transistor radio and marveling how clever it was to mount axial-leaded components (resistors and capacitors, mostly) perpendicular to the circuit board. The practice never caught on...
  7. hevans1944

    Motion sensing mouse trap

    My wife discovered that putting a small quantity of used cooking oil, about a quarter-cup, in a small jar with a screw-on lid and setting it out for the mice to investigate worked really well. The mouse gets their front paws wet, falls into the jar, and can't get out. Sounds absurd, but try it...
  8. hevans1944

    CAMA-AFM31 USB Capacitive Fingerprint Module with FPC1020 pin configuration

    The control board is different from the one you show, but you might be able to use the information provided at this website. Or maybe you could call one of the support telephone numbers that can be found here. Note this is an OEM product, so some software is required for your specific application.
  9. hevans1944

    When and why would you use a capacitor?

    Capacitors are often used for temporary electrical energy storage. The common photo-flash is a good example. The energy-storage capabilitiy of a capacitor is relatively small, compared to other devices such an electro-chemical battery or a spinning fly-wheel, but it has the advantage of rapid...
  10. hevans1944

    Quiz buzzer system

    Not really. In the schematic shown in post #2, the two NAND gates form an RS latch as long as the dual 2-bit latches are in transparent, pass-through, mode... which they will be as long as the active-low Latch Enable inputs (pins 4 and 13) are high, i.e., NAND gate 2Y output is high. Pressing...
  11. hevans1944

    Quiz buzzer system

    I am confused. If the LE input is initially held low by R1, and none of the outputs is yet high, and all the inputs are pulled low by RN1, and none of the switches SW1 through SW8 are closed, how does closing any of SW1 through SW8 propagate a logic one output to LEDs D1 through D8 and hence...
  12. hevans1944

    74HC390 table of pin connections?

    Well, actually you can if you understand how the counters work. Review this Texas Instruments datasheet for this obsolete and no longer manufactured part. Then breadboard a trial circuit using a low-speed clock, typically a de-bounced push-button switch, and a logic probe to see what is going on.
  13. hevans1944

    Hello

    Welcome to EP, @Jim Trucks. Hop - AC8NS
  14. hevans1944

    Finding a good soldering iron....

    ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd with a little imagination translates to Fear the Antipodes! Good advice. Seems to be a rather inhospitable bit of kit.
  15. hevans1944

    Finding a good soldering iron....

    Yep, you have to fit the flux to the job. One of my uncles was a practicing (non-degree) chemist working for the US Steel coal mines in West (by God) Virginia during the 1940s and 1950s when his father (my grandfather) asked him to whip up a jar of soldering flux. I am almost certain it was a...
  16. hevans1944

    Finding a good soldering iron....

    Well, of course it is. That's why you want to make sure you wash the residual flux off the joint. If flux weren't corrosive, how could you expect it to remove non-conductive compounds that prevent soldering two metals together? I keep two spools of solder alloys handy: 60%Sn-40%Pb (common 60/40...
  17. hevans1944

    Where to buy EPROM window stickers?

    Not very. The EEPROM requires short-wave ultraviolet light to erase data. Even thin paper will absorb those wavelengths.
  18. hevans1944

    How does a multimeter's continuity function work?

    Most continuity functions on multimeters apply a fairly large "compliance voltage" in a constant-current "measuring mode" so they are really measuring resistance as a voltage drop between the two probes. As @davenn said, they usually produce a "beep" if the measured resistance is low enough to...
  19. hevans1944

    Basic Electronics

    Voltage is never measured AT a point. It is always measured BETWEEN two points. The voltage drop across a resistor is given by Ohm's Law to be the product of the current through the resistor and the resistance value: V = (I)(R), where V is measured in volts, I is measured in amperes, and R is...
  20. hevans1944

    am outta here

    Happy trails, Donkey! I am gonna miss ya.
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