Digital Piano repair help.

Discussion in 'General Electronics Chat' started by SteveHow, Jul 2, 2012.

  1. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
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    Hello,


    I was wondering if someone could help look over a schematic for me. This Yamaha CVP-50 is not playing any sounds from its keyboard, nor is there any power to the display. I tested the power supply and all seems ok. Can you guys recommend someone who has patients, skill and time to help me out.

    The Amplifier is working.

    This is out of my skill level and I don't know where to look next. I am hoping its not a failed Main IC, but having no 2 x 7 segment LED display, its seem it must be still a power issue.


    Thanks
    Steve

    Australia.
     
    Last edited: Aug 3, 2012
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC

    Do you have a schematic?
     
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  3. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2

    Yes, I the full official Service Manual I purchased from Yamaha (PDF).


    Thanks Bill, can I send it or upload it ?

    I am greatfull for any help, and I don't expect to repair this over night.


    Do I have to upload externally ?
     
    Last edited: Jul 2, 2012
  4. crutschow

    Expert

    Mar 14, 2008
    12,969
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    You can post it from this forum thread. Just go to Attachments icon (the paper clip) and select the PDF as the Chose File to Upload. Then go back to the paper clip to attach it to your thread.
     
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  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I'm not a doctor, but have you checked the connection on the jack? Is it good and snug? These barrel-type (I'm assuming that's what it is) connector jacks have a habit of "stretching out" inside so the connector no longer connects well.
     
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  6. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    I learned to hate these DC jacks when after about 1/2 year the wall adapter plug on my SEGA master system started to cause problems. Finally even the 7805 inside burned out. I don't know how many times I turned and twisted the plug because of bad connections.

    I have my third thermo label printer now which I only run on batteries- the previous one's failed only because of these crazy DC jacks, and abnormal voltage requirement (7V). Also a LCD photo frame was ruined instantly one day, simply having 20 wall adapters around, and I connected one with 12V, very similar in size/shape.
     
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  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    A guy brought me a laptop with a bad jack and wanted me to fix it. I found a part on newark that I thought was a "likely" replacement but he didn't want to pay for it. so I removed the jack, cut the barrell off his power cord and soldered it straight to the board where the jack was. He was happy with that.
     
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  8. PackratKing

    Well-Known Member

    Jul 13, 2008
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    One possible snafu with a liquid crystal display, is the silicon-carbon connector block which sits clamped between the pcb and the glass sandwich comprising the lcd. These are dang near impossible to repair, considering that the traces it must contact to on the lcd glass, are horrendously fragile.
    Best I can say, is observe how it is assembled, remove the connector block flush the surfaces gently with a little ethanol - preferably 200 proof everclear, air dry, handle parts after this with any suitable cleaned tool except fingers, and you may get lucky
     
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  9. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
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    Hello, thank you all for your comments. I have been working on this and I am about to write up my findings. I will also post the schematic externally, as its over this forums size limit.

    I have been doing some testing and I wanted to wait till I have a real question. At this stage I am pretty lost where to look next. This is a complex unit, the schematics take time to get ones head around. (Well it is for me) At least now I can write up my findings in the hope that someone can point me where to look next.

    Thanks Steve


    Note, I will be writing up my notes and uploading within the next hour.

    I am almost 100% sure its not a power issue now. Its IC level. :( (IMHO)
     
    Last edited: Jul 16, 2012
  10. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2
    Hi, and thanks for helping me out.


    Symptoms.
    When powered ON, PS relay switches on, which I consider normal. Red LED lights for a moment on FDD as it spins. (Assuming its spins)
    Amplifier is working (see below).
    No keyboard sounds at all.

    No other LED or LED display lights. Now I am thinking is there a POWER ON LED, I haven't checked that, but if there is, it will be no doubt OFF. (UPDate, I checked, there is NO POWER ON LED)

    (Note that there are many LEDs and a Dedicated LED Numeric display, on the front panel, and none light. The control panel is "seemingly" completely dead.)

    Power supply checked, +5V, +12V, -12V all good. (There is a B+ on the schematic, no idea what it is or how to test it) Note, the PS is an internal Transformer driven unit, not a Switch MODE.

    Amp is working. I can hear the AMP working/hissing and the Volume control does effect its level. This also confirms, IMHO that the Power supply is working, namely the Pos/Neg 12V lines.

    Finally I have tested power (+5) is getting to the 2 CPUs, namely IC20 and IC5. Why did I check these? Because I believe that somewhere in the circuit something is not telling the unit to turn on. My thinking is that these 2 main CPUs are at the heart of the system and need to run their code which then give green lights to other ICs.

    I can't think of anything else to add.

    I would be much appreciative if someone could pinpoint what might be the problem. The size of this project is over my head. I have electronics training, but this is way out of my league. BTW, I have an Oscilloscope, if someone needs me to check anything.

    Schematic Service Manual.
    (See Pages 48-49 for Circuit diagrams)
    http://www.sendspace.com/file/9xy7u1
    Note the download link is currently dead, if someone needs to take a look at this schematic let me know.

    Thanks
    Steve.


    Would the next step be to check the Crystals on the CPUs ? (Just a thought) As you can see I need major help.
    I personally think one of the ICs has fallen over. But how do I narrow down the hunt?
    Also, I was going to check if the was any MIDI activity, but have not at this stage. ???
     
    Last edited: Aug 15, 2012
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Hi, sorry, I follow the link for the file and I get one of those file sharing sites with way too many deceptive "download now" buttons. I tried 3 and all of them were bogus executable files, not a schematic. I'm not installing them. Is there really a link to an actual schematic there?

    EDIT: never mind, it's the smallest link on the page "download from sendspace"
     
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  12. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
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    NOTE (TO DOWNLOAD PDF Service Manual, got to site mentioned. and scroll down to "Click here to start download from sendspace" in the BLUE box with the BLUE ARROW. (Other download links are deceiving)

    Please DON"T click on "Click here to start downloading.."

    I was unable to edit my post to add this update. Some file sharing site can be a mine field to navigate. :(
    I probably could have found a better file sharing site, apologies for the confusion.
     
    Last edited: Jul 16, 2012
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  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Sorry SteveHow. That thing would be a bear for me troubleshoot even if I had it in front of me. I won't be much help, but there's plenty of experts around who might be able to help...
     
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  14. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2

    Thanks you for having a look, much appreciated. I would rather, as you have, people give it to me straight, rather than make out they know more that they do. Waists everyones time.

    I understand this is a huge project and ask of peoples time.

    Kind Regards
    Steve


    EDIT: I have the patience and don't expect anyone to run around for me, I am looking for expert knowledge. I am willing to do all the leg work needed, i.e hunt for IC Data Sheets if needed. All I need is some pointers, to get me started.
     
    Last edited: Jul 16, 2012
  15. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
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    HD64180 CPU Data Sheet
     
  16. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Most of what you've done so far seems reasonable. You mentioned that there were several LEDs. If any of them are board level, not displayed to the exterior of the housing, they merit some attention as they're there to indicate the status of the various subsystems for diagnostic purposes.

    You might use your oscilloscope to check for excess ripple on your power supply rails and look for and test any subsidiary supplies developed on the boards.

    If that all checks out, the next thing would be to use your scope to look for a good clock signal.

    This is all generic advice since I haven't, and probably won't bother to look at the schematics. It's quite tedious with a smart phone you know. :(
     
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  17. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2

    Thank you, this is encouraging and gives me some things to look at. I am getting a little disheartened but I must stay patient and positive and look at this as a challenge. Its not life of death stuff, but where its sitting is in the way and it weighs a ton.

    How do I check the each clock/crystal, can I put my CRO directly across them. For example IC20 CPU has a 16MHz Crystal connected across PINS Labeled, XTAL and EXTAL. Can I just connect my CRO across these 2 PINS, to measure the frequency. I have never checked a Crystal before. IC5 (SUB CPU) also has Pins PINS Labeled, XTAL and EXTAL, but with a 12 MHz Crystal hanging off it. What waveform would I expect so see, Square/Sine Pulse ?

    And Yes, I will check subsidiary Supplies, and check for excess ripple. (I can do that).


    Regards
    Steve.

    P.S There is no way you could look at that schematic on a phone, its hard enough on a PC. :)


    EDIT: There are no board level diagnostic LEDs. However there is a diagnostic test as outlined in the service manual, but the Triple 7 Segment LED display needs to be functional.

    And of course there is the possibility that there is more than one fault, I don't know the history of the unit or who has been goofin with it. I am still assuming only one fault at this stage.
     
    Last edited: Jul 16, 2012
  18. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I would just probe for the clock signal on the clock input of the IC(s).

    By the way, are there any fuses hiding anywhere. Pico fuses and micro fuses can easily be overlooked if you haven't seen them before.
     
  19. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2

    Good question, I will have to examine further for the Pico/micro fuses. And correct, I am not totally familiar with what they look like. I will look through the Service Manual and see if any are noted.

    Thanks again.
     
  20. SteveHow

    Thread Starter Member

    Jul 2, 2012
    78
    2
    Assuming one fault that has taken out 2 functions, the Keyboard/sound and the Control Panel. There must be a common factor ?
     
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