Yamaha Keyboard P-95 sound problem (speakers & headphones)

Discussion in 'Technical Repair' started by GermanCoca, Sep 20, 2017.

  1. GermanCoca

    Thread Starter New Member

    Sep 20, 2017
    4
    9
    Hello everyone,

    I have a Yamaha P-95 that after approximately one year of being stored, currently is not emmiting any sound from either speakers or headphone plugs.

    I checked the functionality of the Keyboard and the MIDI processing was ok. I tried all the quick solutions out there (enabling internal audio, check if something is blocking the headphone plugs, cleaned volume key), I figured it had to be the amp board so I decided to open it and see if there was a component with blackened leads, or some visual clue of the problem, but unluckily the problem wasn't so evident and there were no faulty components to be seen.

    Looking for schematics I came across a post in this forum that stated a similar problem:
    https://forum.allaboutcircuits.com/threads/speaker-relay-on-yamaha-r-90-receiver-not-closing.77234/
    In wich it states that the keyboard has a protection circuitry that closes the speaker feed relay if after a few seconds from turning on the output stage is found healthy. This is indeed the case as I can hear the relay closing, and even opening again each time I connect headphones on either plug.

    The strange part is that, trying to troubleshoot the situation, I unplugged the headphones board and after reconnecting it, the problem went away... unitl I turned the keyboard off and on.

    Sadly the service manual has no schematics of any board. It only shows the disassembly of the unit.

    Any thoughts on what may be the problem?

    Thanks for reading,
    German.
     
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  2. MrChips

    Moderator

    Oct 2, 2009
    16,445
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    We will try our best to fix your problem. It would really help if you can locate the schematics. Along with that, photos of the actual unit will give us some idea of the design and layout of all components. Post any links to the service manual. Post well focused photos of the insides of the unit.
     
  3. GermanCoca

    Thread Starter New Member

    Sep 20, 2017
    4
    9
    Hello again,
    Thanks for the quick response!

    I'm attaching the service manual for the P-95. Furthering my research a little I found that the AM board in this model is the same as the P-85, and that model's manual has a lot of information, including schematics. I'm attaching that manual too.

    Thank you!
     
    UrazC likes this.
  4. GermanCoca

    Thread Starter New Member

    Sep 20, 2017
    4
    9
    after a LOT of troubleshooting, it would seem that the problem was a faulty electrolytic capacitor (component C217 on the AM board schematics). I will get a replacement and confirm if it is a success.
     
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  5. MrChips

    Moderator

    Oct 2, 2009
    16,445
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    Glad you found something. I really didn't want to have to open my P-105 to compare it with yours.

    Do you mind saying briefly how you found the bad capacitor? This could be useful information for someone else later.
     
  6. GermanCoca

    Thread Starter New Member

    Sep 20, 2017
    4
    9
    Hello again,
    I finally replaced the electrolytic capacitor and the keyboard started working again!.
    Trying to figure if it was a problem with the headphones board, or a security meassure on the main CPU (which was unlikely, as the way that the CPU has handle this is to open the relay that controls the speaker input, and I could hear it closing each time I turned the keyboard on), and because unpluging the board actually triggers said meassure and opens the relay, I desolder these 2 capacitors to open the headphone circuit.

    This efectively made the speakers work again, and after resoldering the first capacitor and testing the unit, the right channel of the headphones started working, so I figured that it had to be the other capacitor. Replaced it and both channels worked properly.
     
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  7. UrazC

    New Member

    Feb 13, 2018
    1
    2
    Hello GermanCoca,

    Thank you SOOOOOOOOOOOO much. I had the same problem and solved it with a single shot, thanks to your experience.

    I would like to add a small contribution. To test whether the problem is on the headphone path, it is easier just to disconnect the HP board completely and connect HPSW node to GND on AM board, instead of desoldering C217 and C216. If the problem is the same, the speakers should start working.

    I am curious if this is just a coincidence that among all other capacitors, the same were problematic in both cases. Here is the only misuse I can think of: I recently bought a sennheiser hd558 headphone whose cable can be detached from its speaker. When I was using my piano I used 3m cable and when listening to music, I switched to 1.2 m cable while leaving the 3m cable on piano, with its other end open. I touched that open end many times when I switched from playing on the piano and listening to the music. Do you guys have any idea if this could cause the harm mentioned above?

    Thanks again GermanCoca!
     
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  8. MisterBill2

    Active Member

    Jan 23, 2018
    893
    163
    According to some sources aluminum electrolytic capacitors have a finite lifetime that is not that many hours, and according to one Sony repair tech that I knew, Rubycon brand capacitors routinely failed for no apparent reason. In your keyboard, while replacing the capacitors I would resolder the connections of the other parts as well. Sometimes soldered connections fail, if they were done at an excessive temperature..
     
  9. elektron10

    New Member

    Jul 3, 2014
    1
    1
    Hi. Since the cable was connected to an OUTPUT, most likely this would not cause the problem. Outputs are usually the lower impedance end of things, and they are accustomed to wiggling copper wire coils around in a strong magnetic field, so they HAVE to be robust and protected from back EMF, etc. Usually, something like this would happen to a high-impedance INPUT such as where there would be some kind of MOS device without adequate protection. I worked on a lot of Yamaha equipment many years ago, and although in some cases, it seems that the one-sided phenolic PCB's they used to use were a bit flimsy for my taste, they seemed to have truly robust designs with clamp diodes and/or transient voltage suppression set to a voltage only slightly above the expected input voltages. The Japanese are truly skilled at cost/risk analysis because they design everything in such a way that minimizes cost without compromising quality. If I was one of their engineers, I would probably insist on FR4 glass-epoxy boards because they don't cost all that much more than the phenolic and it is a bit more rugged. Nice job of fixing your problem. The best way is NEVER re-invent the wheel. If someone else has a similar problem, by all means, try their solution.

    As an aside, there was one Yamaha keyboard that had me flummoxed at one point. It just refused to function. There was power everywhere, but the processor clock seemed to be halted. It was a brand new one brought back to the music store where I had my shop. There were no obvious shorts that I could find, and other than a halted clock, outputs from chips were correct for the inputs. While powered up, I bounced the ends on the bench, and suddenly it was "fixed." All functionality returned. I knew it had to be something silly, because I know that as big as Yamaha is, they would QC test their products like crazy and they all have to work before they package them for shipping. So I know they to vibrational testing as well. I unplugged the unit and started jostling it again, and there it was. On this particular keyboard, it was an all through-hole design, single-sided phenolic. To make the connections on the top of the board, they use bare wire jumpers. And there it was. A piece of trimmed bare-wire jumper without its bends and it would roll under two or three others. Removed it and back home it went! It just goes to show that in a lot of cases, the problem is usually something silly like that. And kudos to GermanCoca for excellent troubleshooting!
     
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  10. poixninja

    New Member

    Jun 4, 2018
    1
    0

    I know this is pretty old, however i had a customer come in for a repair of this keyboard with the same issue. This worked flawlessly and would like to thank you because she uses her keyboard to help cope with her depression, and being able to get it back to her quickly was very important to me. Thank you again!!
     
  11. MrChips

    Moderator

    Oct 2, 2009
    16,445
    5,052
    Welcome to AAC!

    Glad that you were able to resolve your problem promptly with help from AAC!
     
  12. MisterBill2

    Active Member

    Jan 23, 2018
    893
    163
    I have discovered that this "group" has quite a few folks who are very expert in their areas, as well as a number of beginners whose need to be given a lot of help is impressive. That is why I keep revisiting!
     
  13. hedegaardmatthesen

    New Member

    Aug 6, 2018
    3
    0
    My girlfriend has this keyboard with the exact same issue. We want to replace the electrolytic capacitors but I am wondering if you can tell me which side is ground when soldering the capacitors in place? If I remember correct the long pin on the capacitor is + and the shorter is -
     
  14. MrChips

    Moderator

    Oct 2, 2009
    16,445
    5,052
    Electrolytic capacitors have markings on the body to indicate polarity. The negative polarity is usually indicated with minus symbol. The negative lead is connected to a point lower in voltage than the positive lead. No lead is ground.

    [​IMG]
     
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  15. hedegaardmatthesen

    New Member

    Aug 6, 2018
    3
    0
    Thank you for the reply! Now I should be able to do the job :)

    I acturally meant where on the PCB the negative and positive terminals should be connected to. I didn't know that the blue band indicates the negative terminal. I'll just place the new capacitors with the band in the same position as the old ones.
     
  16. hedegaardmatthesen

    New Member

    Aug 6, 2018
    3
    0
    Update: After replacing the two capacitors everything works! Super easy and cheap repair except for all the screws holding the keyboard together :O
     
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