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Repair R/C Car Reciever

Discussion in 'Electronic Repair' started by [email protected], Dec 18, 2006.

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  1. Guest

    Hello, I am totally new in this, but I am hoping someone here can give
    me some tips.

    I have a R/C car reciever (Kyosho Mini-z) which has become very poor
    range recently. I have checked battery both on the transmitter and at
    the car, crystal, and wiring, they all seems to be fine. The symptom
    is if I have both the transmitter and the car switched on, the car will
    twitch (the servo) badly, and the motor is start to running on its own
    without me pressing anything.

    All my electronic knowledge are only from my classes during college,
    but I don't have any troubleshooting experience at all. The only test
    tool I have is a multimeter, can only test resistance, diode, and AC/DC
    voltage. So, I am hoping if anyone can tell me how I can go about to
    find out what component has become culprit. And of course the next
    question, would be where to buy replacement.

    Many many many thanks!
  2. What happens if the transmitter is switched off?
  3. Guest

    The car will totally stop twitching. So, I thougt it could be
    transmitter that was bad, but I tried with 3 different transmitter and
    still the same... Looks as if the receiver has problem treating the
    incoming signal?
  4. Looks like it is having problems round the detector / decoder areas. You
    probably need more then a DMM to fix this.
  5. Guest

    How should I go about to start troubleshooting? And what kind of test
    tool I would need?
  6. Don Bowey

    Don Bowey Guest

    What type of receiver is it? Regen, single or dual conversion?

  7. Without a service manual, I would need an oscilloscope with an RF probe for
  8. Guest

    Hi Don, I wish I can answer your question. All I know is this is a 27
    Mhz AM receiver for R/C car. Do you think it will be too much for a
    beginer to fix? I mean the circuit looks pretty simple, so I figured I
    want to give it try.
  9. Don Bowey

    Don Bowey Guest

    If the receiver does NOT have a crystal, it is probably a regen receiver and
    you might be able to retune it to the transmitter. If there is no crystal,
    look over the receiver to see if it has small adjustable capacitors and/or
    coils that have a slug inside that can be adjusted. You will need plastic
    tools to make any adjustments. Let me know what you find.

    If the receiver has a crystal, be sure it is seated in its holder.

    If it is not a regen, then it needs tools such as a scope and signal
    generator in the hands of someone who can trouble shoot without having a

    Post the name of the city where you live and maybe someone will volunteer to

  10. Where are you located?

    I repair radio systems for a large hobby shop in the MidWest, just north
    of St. Louis, MO.

    Have been doing R/C repairs since the 1960's

    Will help if I can.

    Make and model of car and radio?

  11. Franc Zabkar

    Franc Zabkar Guest

    This makes no sense. AFAIK the transmitter should not transmit
    anything until you move the joystick, otherwise its 9V (?) battery
    would quickly go flat.

    - Franc Zabkar
  12. Guest

    Hugh, It is one of those ESC receiver combo for micro size R/C car.
    May I ask you how much it would be to fix?

    Franc, the transmitter for radio control car would start transmitting
    immediately after you turned on, that's why it is a MUST for hobbist to
    switch on transmitter before turning on the car.
  13. Franc Zabkar

    Franc Zabkar Guest

    I've repaired quite a few toy R/C cars and don't recall ever
    encountering one where the transmitter would transmit continuously
    without user action. In fact some remotes had no on/off switch. Maybe
    your hobbyist vehicles behave differently, but it still begs the
    question, what is it that the transmitter is transmitting? I can
    understand it signalling forward/reverse/left/right/turbo, but why
    would it signal a "do nothing" command?

    - Franc Zabkar
  14. Guest

    I would think the hobby grade transmitter are quite different than the
    toy grade RC. With the hobby grade transmitter, they are not only with
    4 signal, but are propportional. So, there are steer trim and throttle
    trim noob/button so that you adjust the car's alignment or throttle at
    its neutral position. So, it is also dangerous for nitro or high power
    electric car to switch on the power on the car first before the
    transmitter is on. I don't exactly know how things work, but I think
    the transmitter should be on to keep the car in neutral position before
    applying throttle or steering.

    But back to my very desperate question [I have no car to play for
    almost two weeks now :-( ], I have heard from other hobbyists
    mentioned when they have the powered on transmitter antenna
    accidentally touch the antenna would fry the car's receiver; and I have
    heard they fix the receiver by replace an inductor. I guess the
    inductor on the circuit board usually begin with "L"? Do you think I
    can check if the inductors are blown without investing with a probe or
    occiloscope by using just a DMM?
  15. Don Bowey

    Don Bowey Guest

    Are you certain the transmitter and receiver are on the same frequency?
  16. JW

    JW Guest

    From what I remember when I was a boy flying R/C planes (back in the late
    70's), switching on the transmitter first keeps the servos from getting
    "jammed" at the far end of their travel, possibly damaging the gears.
    Whether this was a myth or not, or whether the current crop of RC stuff is
    subject to this...?

    FWIW, I have seen them lurch suddenly in one direction when turning on the
    transmitter after the receiver. (I just HAD to try it :)
  17. Franc Zabkar

    Franc Zabkar Guest

    A simple DMM will only tell you if the inductor is open circuit. It
    cannot distinguish between a good inductor and one with shorted turns.

    - Franc Zabkar
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