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Yamaha PS-35

Discussion in 'Datasheets, Manuals and Component Identification' started by Dirty Contact, Nov 24, 2012.

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  1. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    My granddaughter has come up with one of these keyboards. It is so faint and some keys do not work. I have opened it up and wiped out the coffee! I thought it was battery leakage at first but it tastes OK! The volume control does nothing, the transposer switch seems to work on two positions, the headphones receive nothing, it does not work on batteries BUT it does play faintly and the orchestra and rythm keys all work. Ther "Fill In" doesn't do anything either. I suspect the incoming supply could be at fault and amplification circuits. Is it for the bin??? Or am I likely to be able to do anything? A circuit would be useful if anybody has one.
    The power supply is 12v at 1amp which is a bit low on power I guess.
     
    Last edited: Nov 24, 2012
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is that the correct power supply?
     
  3. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    It is not the Power Supply supplied with the machine but carries an adequate rating. Is it likely to cause a problem?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    As long as the power supply has an adequate rating (similar voltage, equal or greater current) then it is unlikely to be the issue.

    Is the output clean, or distorted? It may be the amplifier.
     
  5. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Not distorted but very faint. The lower octave is almost below hearing. I have suspected the amplifier from the start but I cannot identfy it on the boards and don't know how to test it.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Maybe some photos would be good right now...
     
  7. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Last edited: Jan 24, 2013
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, tell me where the speaker wires connect to the board. It's hard to tell because of that foam looking sheath they're in.

    Then tell me what is written on the three closest ICs to that.
     
  9. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Left Spkr (Yellow Blue & Grey) Rt. Speaker (Purple,Blk & White) Both into multiplug top RH end. I have lifted the main board to trace them into largish capacitors one 2200uF at 16v four others at 1000uf at 10v. These are at the top, very right hand end of the board. The nearest chip is M5323L 2704. There is a very well cooled 7805 244G three pin and under the cooling fins are two LA 4128 3AB all look to be involved in the speakers output. Interestingly enough I noted that the board has been repaired before, underneath, several of the smaller ceramic capacitors have been replaced at some time. The soldering looks ok but not vey pretty.
    Regards
    Bob
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's not going to be the 7805.

    Show us a sharp closeup of this region of the board, both sides.
     
  11. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Pics of PS-35

    View attachment 6424

    View attachment 6425

    Not too clear. I can do better if I arrange some better lighting. Flash just burns the picture out!
    You see that I have had to remove the two ICs heat sinks to get their numbers.
     
    Last edited: Jan 24, 2013
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, it's probably better with natural light. Flash (as you observe) isn't wonderful.

    I was wondering about the chips. They looked like they had heatsinks.

    That tells me that there are two amplifier chips, and I expect one to be the left channel and the other the right channel.

    It also pretty much eliminates them as it is unlikely that both would go faulty exactly the same way.

    The problem needs to be something common. It could be the power supply, or the signal generator.

    The capacitors on the underside are "fixes" applied to the board, almost 100% done at time of manufacture. Don't worry about them.

    Also on the underside, I see some "stuff" on the top right corner of the board and those solder joints are maybe a little suspicious. It may be worth cleaning up this area with some alcohol.

    It looks like each amplifier is a dual amplifier and I've got to confirm that there are 2 speakers and each has 2 wires going to it? If that's the case then these are bridged amplifiers and may even be running at a very low voltage.

    I'm trying to locate the power supply connections...

    OK, looking at the top of the board in the orientation you have it. the bottom of those 2 similar chips, and the row of pins toward the bottom of the image. Read the voltage between the bottom left-most pin, and the 5th pin along 1 _ 2 3 4 5 (so 1 and 5)

    Be careful not to short anything out, and don't try playing anything because the amplifiers have no heatsinks. I think I'm expecting to see 5V
     
  13. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Hi Steve, I can confirm the two speakers each with three wires connecting. I did give the colours on one of the posts I made. The voltage across the bottom chip pins 1and 5 is 4.4 volts accompanied by buzzing in the speaker whilst measuring. The similar chip gives 12.4 volts on pins 1and5. The power supply comes in just below the brown arrow shaped mark on the underside of the board and is further identified by one pin being white as it has caught the light on the pic.
    The speaker multi pin socket goes to the 5 pin connector at the top right of the underside pic. of the board.
     
    Last edited: Nov 27, 2012
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    3 wires connecting each speaker. That's weird Can you give me a close up image of a connection to a single speaker. If you can see, are there really three connections into the speaker coil itself?

    Other than old transformers with a field coil, I've never seen a three terminal speaker. I'm assuming it's a centre tap, but why not simply bridge the amplifiers.

    And It also looked to me that the power supplies tot he amplifiers were in parallel and should read exactly the same. I'll have to check I gave you the right pins...

    In any case, a difference between measurements on corresponding pins seems odd.

    Also I would have expected 5V, not 4.4, so maybe there is a problem in the power supply. I'll look again later.
     
  15. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    There are 3 leads to each speaker but the black is common earth on each.
    I mislead you in my last message.... voltage on pins 1 and 5 is 5.5volts on both chips. Not sure how the previous readings varied from this except that I mentioned a buzz in the speaker whilst taking readings and when the 'buzz' is on the reading drops to 4.4. It seems to happen when the probe is touching the body of the chip at the same time as the pin.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    5.5V is OK for a 5V regulator. I'm glad they're the same. You had me worried.

    Was the buzzing you heard on the speakers louder than the sounds from the keyboard?

    Does the volume from the keyboard alter with the volume setting (if it has one)?

    Oh, and does it have a headphone socket? If so, what is the level like there?
     
  17. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Buzzing Noise about same level as keyboard,very low. Vol Control does nothing and there is no output from head phone socket. The transposer switch has come to life tho'. It has 5 up and 5 down positions two of which make a note in each octave sound very "grumpy"!! Pitch control works OK. The plot thickens. I am not 'playing' with it pending instructions from you!
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, I'm wondering about the volume control.

    You clearly have a multimeter of some sort. Can you make a table of resistance values.

    The three rows should be Min vol, mid vol, and max volume (where you turn the pot all the way down, place it in the middle, and finally at full volume.

    There are typically three connections on a pot (stereo will have these repeated). They're almost always in a row, let's call them A, B, and C (for the moment it doesn't matter which way you label them, just be consistent)

    The three columns are the resistance between A-C, A-B, and B-C.

    If it's a stereo pot, repeat the table twice, once for each "gang" of the pot.

    These measurements should be taken with the power off, and leave the wires connected. The results won't be perfect, but they should be highly indicative.

    This is probably a long way of doing what I'd do in real life, but you understand that asking you to "measure the pot and get a feeling for whether or not it's operating" is perhaps a little vague :)
     
  19. KJ6EAD

    KJ6EAD

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    Last edited: Nov 30, 2012
  20. Dirty Contact

    Dirty Contact

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    Nov 24, 2012
    Thanks for your post. I have seen the owners manual which is not a lot of good for servicing as you know. The service book is available in Canada, not cheap and postage doubles the price so I need to establish which is best value. If I can sort it, with help, that's my best option at the moment.
     
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