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  1. Alec_t

    LG Hifi System - LM-K3960

    Looks like the Vcc of IC901 is too high. The Vcc of both ICs should be about 14V, given that both are regulated by the same spec 14V zener diode, a 338. I'd be replacing ZD911 and C909.
  2. Alec_t

    Problems with iPhone 5V car power supply

    Use 8k2 instead of 8k?
  3. Alec_t

    EEG CIRCUIT!!!

    If it were me I'd take the output from the left side of R15, via a 2:1 voltage divider comprising two 4k7 resistors. Incidentally, the sound card usage is questionable, given that some (most?) soundcards have a frequency response which drops off rapidly below 20Hz.
  4. Alec_t

    Current passing for regulator IC's

    Be aware that the contact strips in most breadboards aren't designed to carry heavy currents.
  5. Alec_t

    Can you make my 12v LED light up?

    If the circuit is as per post #9 there is no way Q2 should get hot. The only way it could draw excessive current would be if there were a short circuit between the Q2 collector and ground. I hope you haven't interpreted the blue box shown around R6/D1 as a wire connection :eek:. Can you confirm...
  6. Alec_t

    Circuit to switch off a DC motor

    You could start by fitting limit switches to the gate. Why do you want to wait a couple of seconds before turning the motor off? Wouldn't it be better to turn it off as soon as the gate reaches one of its limit positions?
  7. Alec_t

    Can you make my 12v LED light up?

    If the PWM input is left floating that's not surprising. Connecting the PWM input to ground should turn the green LED off. Credit to your US supplier for helping to resolve things.
  8. Alec_t

    Cassette Tapes that won't play

    Welcome to EP! Muffled sound could be loss of treble due to misaligned heads. Recordings made on one machine will not play well on another unless the head gaps are accurately parallel. 'Print through' from one tape layer to the next is another possible cause when tapes have been stored unused...
  9. Alec_t

    Ultrasonic sonar

    I suspect the mechanical resonance frequency will be modified somewhat depending on the acoustic impedance that the transducer has to drive. You may, therefore, need some dynamic tuning arrangement. Are commercial transmitter circuits self-tuned by feedback?
  10. Alec_t

    AC motor speed control

    I doubt a sewing machine motor would be powerful enough for your application.
  11. Alec_t

    LG Hifi System - LM-K3960

    The circuit seems to have several circuit commons. It's not clear which one is 'ground' in this context. Please use the component designators on the schematic when referring to test points and components. Can you measure (EXTREMELY CAREFULLY, hands free,in view of the LETHAL voltages present in...
  12. Alec_t

    Peak detector to A/D of PIC

    Unlikely, unless the A/D input is duff. How are you 'seeing' the signal?
  13. Alec_t

    Ultrasonic sonar

    Since the wanted echo signal is likely to have an amplitude at least three orders of magnitude lower than the transmitted pulse you will need multiple amplification stages in the receiver section. What is the purpose of R2?
  14. Alec_t

    LG Hifi System - LM-K3960

    Which one? I can see at leat 3 on the schematic.
  15. Alec_t

    Unable to read frequency of a tone signal with a frequency meter.

    Glad you got it sorted.
  16. Alec_t

    Unable to read frequency of a tone signal with a frequency meter.

    Your frequency meter ought to respond to signal A (at pin 11) correctly, providing the meter input impedance is at least a few kΩ and the circuit/meter grounds are commoned.
  17. Alec_t

    Is it possible for a MOSFET to work intermittently?

    Mis-firing due to corrosion in the coil pack?
  18. Alec_t

    Ultrasonic sonar

    Not if the op-amp has a dual-polarity supply. What is the purpose of R4?
  19. Alec_t

    elastomeric Zebra connectors

    Methinks that would result in not all stripes being connected.
  20. Alec_t

    Ultrasonic sonar

    Its non-inverting input has no DC path to the negative rail for the input bias current.
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