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Casio Keyboard: no power

Discussion in 'Troubleshooting and Repair' started by starcott, Oct 8, 2011.

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  1. starcott

    starcott

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    0
    Oct 8, 2011
    The power 'on' switch on my Casio Keyboard no longer turns it on.

    How do I find out if it is a faulty switch? It is a DPDT slide switch with 6 soldered terminals into the circuit board. There is also a red LED which should light up when the power is on. If the LED had failed, would this prevent the power being turned on?

    If the switch terminals are numbered 1,2 and 3 on the left, and 4,5 and 6 on the right, ( 2 and 5 being middle terminals), I can get continuity as follows:

    Switch 'ON' 2 to 3 and 5 and 6
    3 to left terminal of LED
    2 to left terminal of LED

    Switch 'OFF' 1 to 2 and 4 to 5
    3 to left terminal of LED

    Any help would be much appreciated.

    John
     
  2. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Casio key board

    Hi starcott.
    You need to use a tester or multi meter on the switch to determine whats the on / of contacts configuration, and with no power in the key board is it the switch.

    The continuity tester usually a buzzer lets you now if continuity exists or an open circuit.

    What power do you use, battery's or a mains adapter, or just a power mains lead ?. This is where to start, is power going beyond the switch, or is this fine.

    Use a multi meter on AC or DC volts to determine how far the power is going. Select a range on the meter above the working voltage of what you plan on testing, if its mains voltage bare this in mind, its all to easy to forget and get a high voltage shock, so if mains voltage take care.

    But before you call the switch a write off, test how far power is going, a common fault on key boards is the power jack socket solder joints, that's why i asked about the key boards power requirements, if its a mains voltage supply straight to the key board it could be a primary fuse.

    Switches a fairly hardy components, and take a lot of on and off's, although they do fail some times.

    But i would start on the power route first.
    Dave. :)
     
    Last edited: Oct 8, 2011
  3. starcott

    starcott

    6
    0
    Oct 8, 2011
    Casio Keyboard

    Thank you, Dave, for your response.

    I have only been using a mains adapter on 9 volts. The power is certainly getting to the soldered terminals of the jack socket on the PCB, but I don't know how to trace how far the power is travelling along the PCB.

    Should I expect 9 volts going into the switch regardless of the switch position, and 9 volts coming out when the switch is 'on'?

    John
     
  4. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Ok yes 9 volts to the switch, when on is there power the circuit side of the switch, if no then your original suspicion could be correct, the switch.
    Dave. :)
    PS, beyond that we would need some pictures.
     
  5. starcott

    starcott

    6
    0
    Oct 8, 2011
    Connecting pins 2 and 5 to the negative terminal of the mains adapter give readings of 0.68 volts.
    With the switch 'on', pin 3 to negative terminal gives 0.68 volts, pin 6 to negative terminal gives 0.34 volts
     
  6. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Casio key board

    If your only getting 0.68 volts on the input its could be the adaptor, but i guess you selected say 20 volts dc range and tested that ? if yes and you have + 9 volts its the switch or further on. Pic's really do help, of the switch and power board.
    Dave.
     
  7. starcott

    starcott

    6
    0
    Oct 8, 2011
    Casio keyboard No power

    [​IMG]
    [​IMG]

    Very difficult to get photo of switch as 2 pcbs are involved with short leads between them.
    I did use 20 v DC range with a reading of 9v on the adapter terminals but only .68v at the switch.

    The top photo shows the 2 battery connections near top right with the 2 soldered pins of the adapter.
    Halfway down the right hand side there is a 3 core cable which connected to the lower PCB which contains the switch (the second photo). The 3 core cable comes in at the bottom left, the switch on the left further back.

    All connections appear to be good. Would it help if I were able to send any further photos?
     
  8. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Casio key board

    Have you tried a continuity test on the switch, with no power in the key board ? not that this is the problem, but there looks like pcb chemical residue, or it could just be flux, if the adapter works ok and you say it does, then power is getting to the switch, DPDT you need to work out what pins are closed and open circuit when the switch is thrown, again continuity.

    If continuity is fine, then its time to look at the switches solder joints, follow the tracks from the switch, how far can you follow the power to, if there is still nothing on the circuit side of the switch then its probably the switch contacts, or its solder joints, try solvent switch cleaner first, then if still nothing remove the switch with an iron and desolder pump to remove the switch and test its continuity off the pcb, if its not got good continuity replace it, if it has got good continuity clean the pcb pads where the switch was, then resolder, remember orientation of the switch, or whats printed on the display panel will be apposite, ie on will be off, and off will be on.
    Dave. :)
    PS. Try your adapter on some thing else to power up, a bulb or some thing, on occasions regulated adapters fail, the regulator will allow voltage through until its put under load conditions, then it detects a fault and shuts the voltage and current down, some thing else to check, put a load on the adapter, use your meter in series to measure the DC current, few bits of wire is all you need and a bulb resistor or other known load.
     
    Last edited: Oct 9, 2011
  9. starcott

    starcott

    6
    0
    Oct 8, 2011
    When the switch is 'on', I get continuity between pins 2 and 3, and between 5 and 6.

    If I set my meter to 20 volts DC, and put one probe on the negative terminal of the adapter and the other probe on pin 2, the reading is 0.68 volts. I get the same reading with pins 5 and 3, but 0.34 volts on pin 6.

    Does this prove that I am not getting 9 volts to the switch?
     
  10. starcott

    starcott

    6
    0
    Oct 8, 2011
    On the second photo, the 2 pins on the middle left are for the red LED 'power on' indicator.

    It looks as if 2 wires of the 3 core cable from the upper PCB go directly to the LED. If the LED was faulty, would that prevent the power reaching the switch?
     
  11. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
    Your getting nothing really to the switch, test the adapter on another known load as i said in the earlier post, check the jack socket, i know you said you did, but dry or cracked solder joints can be hard to fault find, if it was me i would try what i said already, not just keep testing the switch pins DPDT means what it says it switches two poles on and off, test the adapter as well, a 9 + volt reading is not enough you need to know it works on a load, bulb, resister etc.
    PS,
    Its a process of elimination, you have to go through ALL the motions if the faults not apparent.
    Dave. :)

    Dry solder joints can be re whetted with an iron and a small amount of new solder.
     
  12. Joseph Leblanc

    Joseph Leblanc

    1
    0
    Feb 25, 2016
    Just curious as If it was the on/off switch? I have very same issue with my Casio keyboard.
     
  13. davenn

    davenn Moderator

    13,264
    1,749
    Sep 5, 2009
    since the thread is 5 years old and the OP never came back ... who knows ???
     
  14. davenn

    davenn Moderator

    13,264
    1,749
    Sep 5, 2009
    this is a VERY old thread

    the OP never returned


    thread closed
     
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