Motorcycle Radio

Discussion in 'The Projects Forum' started by tomw, Dec 15, 2008.

  1. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    Hello everyone.I'm probably the newest guy here having just registered on the site.My interest at the moment is with a radio or rather the amp to the radio on a 1983 Honda Goldwing.The radio works but has symptoms like increase/decrease in volume spontaneously,left right speaker works intermittent.I suspect the capacitors may be bad due to age.The replacement capacitors have been ordered from digikey.They will be here Thursday.
    Seaching online for some schematics I came across many 12v dc amps for auto applications and noticed that in some of the schematics the caps show the micro farads but not the voltage.Any idea why?
    If anyone has interest or experience in this area I'd love to hear from you.
    Thanks for putting this site together and allowing me to join.
    Tom
    P.S. Here is a pic of the amp board from the Goldwing.It is a Clarion 2 type radio system.No schematics available that I could find online.
    Component side too.
     
    Last edited: Dec 15, 2008
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Is the intermitting signal always or only when you are driving?
    I see a relays in the midrange of the PCB.
    Are the relays contacts clean?

    Greetings,
    Bertus
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Tom!

    When selecting capacitors, the "rule of thumb" for voltage is at least twice what the maximum expected voltage across the capacitor will be.

    The reason for that is because as the voltage across a capacitor increases, so does it's leakage current. This leakage current will cause the capacitor to heat up; in severe cases it will boil the electrolyte and rupture the case explosively.

    Automotive environments are pretty severe; motorcycles even more so. Your wiring may be suffering from metal fateague (like bending the tab on a pop can back and fourth a bunch of times until it breaks off). Your speaker cones may be shot. If the cone suspension loses it's resiliency, the coil may be contacting the magnet, which will make it sound terrible. The wires that connect the coil in the cone to the terminals are finely braided copper. Check them for corrosion and continuity.
     
  4. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    The signal is intermittant riding or parked,engine running or just power on.
    Forgot to say it has a real hard cracklling noise too.
    I'll check the speaker wires but any idea what the crackling is all about? Thats new.
    Relays contacts clean? you mean like cleaned off with alcohol? That simple?
     
  5. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    I think I just got what you mean by relay contacts clean.The relay has a plastic case over it.Tried to get it off but its really on there,man.Is it one piece? I did notice that the reed inside the relay sparks when I power up and power down.Mean anything?
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You could spend hours and money trying to fix the old amplifier and end up with the same problems or worse. Kiss it good-bye and bury it. A new one won't cost much.
     
  7. floomdoggle

    Senior Member

    Sep 1, 2008
    217
    2
    Tom,
    Usually a cracking sound is somewhere in the output stage, or the speakers. It is not unusual to have a loose wire from the amp to the speakers causing your problem. When that happens, if re-attaching the wires doesn't work, and you still have the cracking sound, start with replacing the speakers. If that doesn't work your amp is shot to the point it is cheaper to replace the system that repair.
    That said, does the cracking sound occur when the front knobs are moved?
    Dan
     
  8. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    I appreciate all the responses here and neither the amp nor I are on life support as far as this amp being made whole goes.
    HOWEVER if I can do something to make it work I'd like to.I'm not opposed to junking it either if it comes to that.
    The cracking sound is upon power up.
    Could I get an amp of lets say 20-30 watts for 12v dc for a car and wire it up? Cheaper is better here after all I'm not paying much attention to the radio at 80mph anyway.But I'm willing to try almost anything here.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Car radios are rated at 200 Whats. That is about 14 Watts into 4 ohms per channel at clipping.

    A TDA7240A amplifier IC for each channel costs only $4.10US today. The datasheet has the schematic and a pcb design.
     
  10. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    Audioguru thank you for that information.I googled the unit and put the schematic and datasheet in my favorites.
    One question please.I see on this unit as I have on others that the capacitors are marked such as .22 micro farads or 220 mircro farads but with no voltage noted per each capacitor.
    How can I know what the caps are rated at? If not noted in the schematic?
    Also if one was to build such a unit what PCB would be used? A prototype board?
    Thank you.
     
  11. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    New observations and questions:
    I have +-12v coming in to the board
    I have +-5v at the speaker out pod on the PCB
    Shouldn't the voltage on the speaker wire trace be the same all the way back through one leg of the capacitors?

    Note: Mostly the left speaker works fine when the system is working.
    Right speaker is not dead but struggling to play at all and when it does it plays
    very low.It fades in and out at will.
    Would this fading be controlled by a faulty capacitor opening and closing and thereby allowing voltage to ebb and flow at the speaker making the speaker volume rise and fall?
    I swapped out the old wires for new with the same results.Also swapped in a new speaker.So that seems to
    eliminate a speaker wire problem?
    Anyone?
     
    Last edited: Dec 16, 2008
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The amplifier operates from a 12V supply that goes up to 14.4V. So capacitor voltage ratings of 35V or more is fine.

    The amp can be made on perforated board (use stripboard) but the pins on the amplifier IC are too close together and will need short separate wires to connect to the board.
     
  13. tomw

    Thread Starter New Member

    Dec 15, 2008
    7
    0
    I FIXED IT GUYS! On the three pin connector on the backside of the PCB where the coaxial cable comes in from the "controller unit" the black wire had frayed insulation.I could only tape it up.But when I put power back on...man is sounds like new! Magnifying glass and flash light held on a bias and many hours of slow looking and I found it.
    Thanks for all the thoughts and help.
    I'll be back because now you got me going on making electronic things.
    I'll check in later.
     
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