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  1. KrisBlueNZ

    How to modify switch to always be on.

    If the board is rectifying the mains first, and feeding the heating pad from that, that may have been done to simplify the circuitry - no need for an optoisolator for the switching device. If the heating pad is just standard resistive wire, it shouldn't care whether it receives...
  2. KrisBlueNZ

    seeking explanation on basic led flashing circuit

    Oh dear :-( Bring back the Colin who seemed to understand the circuit. I was beginning to like him.
  3. KrisBlueNZ

    Non Micro-Controller LED Array Control?

    Well, microcontrollers aren't $30 (unless you want some ultra-fast high-tech device out of a gigabit Ethernet product). Small PIC microcontrollers start around USD 0.50 in 1-up quantities and around USD 0.35 in tube quantities, and those are retail prices. So they're actually cheaper than two or...
  4. KrisBlueNZ

    seeking explanation on basic led flashing circuit

    Hey Colin! That's a pretty good description! I just have a few comments. It's not really a matter of "energy in" CT being "passed to" Q1B. The important characteristic about a capacitor is that the voltage across it can only change when current flows through it, or vice versa, kind of like a...
  5. KrisBlueNZ

    Help With Lock Circuit - Transistors

    That's very cool, Hop. I had trouble understanding the description until I realised that the numbers that were lighting up weren't actually on the keys; they were on a completely separate display that you had to put your head up to. Then you pressed the unmarked keys in the positions...
  6. KrisBlueNZ

    Help With Lock Circuit - Transistors

    Hi Reuben and welcome to Electronics Point :-) Your designs seem to show some understanding of circuit design but there are many errors. I'll start with the obvious ones. First of all, you should start by redrawing the circuit with the positive supply rail along the top, and the negative (0V)...
  7. KrisBlueNZ

    seeking explanation on basic led flashing circuit

    I assume you're talking about the simple design in post #10? Yes, after the initial sharp spike on Q1B, both transistors remain saturated. Q1 remains saturated because of its charge storage time, and Q2 remains saturated because Q1 is saturated. No, I don't think so. Have a look at the first...
  8. KrisBlueNZ

    Giving an acoustic piano electric capabilites

    OK, good luck with that!
  9. KrisBlueNZ

    Stage Line 500W amp repair project

    Also, can you measure three more voltages, all around Q7. Leave the link wire in place.
  10. KrisBlueNZ

    Stage Line 500W amp repair project

    Sorry, my mistake. The "N.F." marking on the schematic means "not fitted", so they're not supposed to be there. But could you look into Q7 please.
  11. KrisBlueNZ

    Stage Line 500W amp repair project

    Aha! That's better. Those voltages across R30 and R32 show that current is flowing in the output stage. That's good! And the -1.8 mV measurement on the output is good - the DC voltage at the output should be close to zero. Is the transistor indicated in the picture Q7? If not, can you find...
  12. KrisBlueNZ

    SMD Capacitor identification

    Colin is a man of few words, many of them wrong!
  13. KrisBlueNZ

    Sony Receiver STR - DA555ES Displays "protection fan" when turned on.

    OK, so the short is downstream of the regulators. Unfortunately it's not a direct short so it may not show up with your multimeter. It's quickest to test by reconnecting those three points, one by one, and seeing when the fuse blows. I hope you have some spare fuses! Try reconnecting the...
  14. KrisBlueNZ

    Sony Receiver STR - DA555ES Displays "protection fan" when turned on.

    Yes, you can desolder the whole 5-pin connector if you want.
  15. KrisBlueNZ

    Giving an acoustic piano electric capabilites

    You might be able to use piezo "benders" - see http://www.digikey.com/product-detail/en/7BB-12-9/490-7709-ND/4358149 at about USD 0.30 each. These will generate a short high-voltage pulse when whacked by the hammer, but they may not be very consistent and they might get damaged. Also they're...
  16. KrisBlueNZ

    Giving an acoustic piano electric capabilites

    Hi there and welcome to Electronics Point :-) That's an interesting idea but I really doubt you could do it for less than the cost of a velocity-sensitive MIDI keyboard. Probably not for less than two or three times the cost. The cheapest way to detect velocity is by having two contacts, one...
  17. KrisBlueNZ

    Stage Line 500W amp repair project

    D'oh! I know what's going on. The amplifier is being disabled by the protection circuit. That's why there's no current flowing in any of the stages! You'll need to temporarily bridge Q2's collector and emitter together. That will bypass the protection circuit, but the amplifier will still be...
  18. KrisBlueNZ

    How to modify switch to always be on.

    Good advice on this thread Gryd3 :-) (And Dave.)
  19. KrisBlueNZ

    Need Some Help Figuring Out How to Use the PDSP2112

    Bummer :-( Check your breadboard wiring carefully. It's not hard to bump a wire and pull it out of its hole.
  20. KrisBlueNZ

    Frequency Generator?

    Your fundamental (excuse the pun) problem is the basic accuracy of the frequency source, whatever it is. You can use frequency dividers and highly stable PLLs (phase-locked loops) to scale frequencies up and down, but the difference between the source frequency and its nominal value, expressed...
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