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  1. KrisBlueNZ

    PC power supply

    OK, good. In the first picture, look in the area at the top left, with the two input electrolytics. I can see a couple of vertically mounted resistors peeking out from below the heatsink at the top, near the corner of the board. What value are they? So you've followed the path from the AC input...
  2. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    It's not too difficult to cut a strip between two adjacent holes. Use a sharp blade like a scalpel and cut a V-shaped channel, about 0.25~0.5 mm wide at the top, in the board across the width of the strip.
  3. KrisBlueNZ

    Op-amps and transistors for audio

    The TBA820M is a fairly old device. Its output power at 3.5V into 4 ohms is typically 0.25W. One of the ones I suggested would be a lot louder. The TI TPA6211A produces typically 0.9W into 4 ohms at 3.3V. Re your graphs for log and reverse log potentiometers, you're probably right; it's hard to...
  4. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    Erm... with solder? Here are two options available from Farnell: BI Technologies P140: http://uk.farnell.com/bi-technologies-tt-electronics/p140kv1-f25br10k/pot-rotary-10kohm-20-50mw/dp/1417134 This is the cheapest option. It has six pins in a line, spaced at 2 mm pitch. This doesn't fit...
  5. KrisBlueNZ

    How to take photos of circuit boards

    KrisBlueNZ submitted a new resource: How to take photos of circuit boards - Hints and tips on how to take optimal photos of your circuit boards Read more about this resource...
  6. KrisBlueNZ

    PC power supply

    The resistor (sometimes there are two of them) are standard cylindrical resistors with colour bands, a bit larger than the small resistors. I don't think they're ever SMT. They're normally in the range 100~470 kilohms. Electrically, they're located between the main input electrolytic(s) and the...
  7. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    Cost doesn't just mean expense. But really, it's your project; you do it however you want.
  8. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    I wouldn't do it that way. You don't gain much over using a silicon PNP emitter follower. One less transistor, splitting the heat in two, but at the cost of a dual-gang potentiometer. I wouldn't be too obsessed about the heat issue. I only mentioned it to point out one way that a simulator...
  9. KrisBlueNZ

    Flyback power supply repair help

    Congratulations and good work!
  10. KrisBlueNZ

    PIC guidance needed

    It's a Flash reprogrammable device. You can erase/reprogram it many times using a device programmer. You can't return it to the store or the manufacturer though.
  11. KrisBlueNZ

    Flyback power supply repair help

    OK, well, the optocoupler isn't being energised. The voltage on its anode is low, but that's because all the output voltage rails are low. So now we need to find out whether the controller is being told that the output voltage is high. Cut the track to either the collector or the emitter...
  12. KrisBlueNZ

    Flyback power supply repair help

    Yes, that's a good thing to check too. Measure the voltage between the Adjust pin (the one that's fed from the voltage divider from the output rail) and the anode (0V on the output side). In other words, the voltage across R11. If it's less than the threshold voltage of 2.5V, the TL431 shouldn't...
  13. KrisBlueNZ

    Flyback power supply repair help

    Well, you've made a really good start! You've done your due Google diligence and saved us a lot of time. So the thing is working, but all of the outputs are running at about half voltage? One easy check is R1 in the above diagram. According to the data sheet, a 2M resistor from the M...
  14. KrisBlueNZ

    Speaker Re-Wire

    Hello and welcome to Electronics Point. First, yes, the speaker will be very quiet. That's because the laptop's audio output is only designed to drive headphones. You DO need an amplifier if you want to get good volume from a speaker with a headphone-level signal. Second, the jack plug has...
  15. KrisBlueNZ

    PC power supply

    Hello John and welcome to the Electronics Point forums :-) Problems in PC power supplies are often caused by dry joints, power surges, or electrolytics. The usual result is that the switching device(s) (transistors or MOSFETs) have their voltage or current ratings exceeded, and the magic smoke...
  16. KrisBlueNZ

    basic transistor ckts can produce audio?

    Well, a Class A power amplifier is actually the same configuration as a small-signal amplifier. You can use a voltage divider for the base, and/or collector feedback, self-bias (JFET or toob), and emitter degeneration. But to drive a speaker (typically 8 ohms), you need a pretty low output...
  17. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    Kind of. A regulator contains an op-amp. But they're not really interchangeable.
  18. KrisBlueNZ

    mosfet circuit?

    I'm not sure you understood what I wrote. No doubt the card has a crystal on it, but that doesn't mean that the cycle time of the servo control signal is fixed, and changing the crystal will affect everything that the micro on that card does, not just the pulse width. You can use your...
  19. KrisBlueNZ

    AVR sound sensor Circuit diagram required

    You could start by looking at this complete AVR-based sound detector project: http://tinkerlog.com/2007/05/20/cheap-sound-sensor-for-avr/ I found it with this amazing new search engine. It's called Google. I just went to http://www.google.com and typed in sound detector AVR, and that was the...
  20. KrisBlueNZ

    Eye Movement Desensitization Rehabilitation device

    Not easily, not that I know of. The closest option is a negative LDO regulator.
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