Home Forums General Chat Technics SX-PX 74M Repair Help Needed

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  • #8787

    mschenkelberg
    Participant
    Post count: 4

    Hi there,

     

    im owner of a Technics SX-PX 74M E-Piano wich has issues with the keystroke dynamic.

    The notes D, fis and ais are allways played on maximum volume. This occures on all octaves.

    Playing the Piano from an external MIDI Keyboard and Demo Tracks are fine.

    All affected keys share the same ROW Lines in the Keyboard Matrix.

     

    It may be a issue with the soldering or with the main ciruit on the keyboard pcb.

     

    Can anyone help me to find a spare semiconductor called  M7U042-016 for this Keyboard?

     

    Thank you

     

     

Viewing 6 replies - 1 through 6 (of 6 total)
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  • Admin
    Keymaster
    Post count: 68

    hi @mschenkelberg

    I’m not going to be able to help you directly because I don’t have the engineering skills.

    Here is a link to a post by Dave Tutt which isn’t directly relevant but may be of interest. I remember Dave being involved in a thread discussing a similar issue to yours but I haven’t been able to find it quickly.

    http://technicskn7000.com/kn7000-forums/technics-keyboards-repairs/note-sometimes-registers-louder-than-pressed-digital-ensemble-sx-pr305/

    To read all of Dave’s posts you can access them via his profile. To do that you need a Free or VIP Plan (get one from the downloads menu) and you need to enable your Legacy Connection (which you can do on the front page of this website when you have a Plan).

    You might also be able to get hold of Dave directly, we haven’t been in touch recently. His website is:

    http://www.tutt-technology.co.uk/

    Best wishes,
    Mike

    If architecture is frozen music then music must be liquid architecture. Quincy Jones

    mschenkelberg
    Participant
    Post count: 4

    Hi Mike, thank yo for your response.

     

    I followed your advice an read all posts from Dave Tutt. Today i did a complete disassembly of my key assy. I cleaned the whole mechanics without finding anything which looks not ok.

    After this i did check the circuit board of the keyboard matrix.

    All wires are ok, no bad soldering, All diodes are ok, the rubber switches are all working the only thing i did find is that the resistance one some rubber switches ist higher than others.

    On most Switches i measure about 60 OHMS.  Some switches are at about 100 OHMS.

    Im afraid that my problem ist coming from defective rubber contacts.

     

    Does anyone her know where i can get replacements for this part? Or ist there a way to fix the rubber parts?

     

    Thanks for your help

     

    Martin

     

    Admin
    Keymaster
    Post count: 68

    Hi Martin,

    This is a very common issue that I’ve encountered many times and ‘fixed’ myself. When I first encountered it I bought contacts from Technics (cost a fortune). Later on, Technics couldn’t supply them so I used a technique of swapping the contacts from keys I didn’t use very much. Finally, I have resorted to buying broken-down keyboards just to get the contacts (you can usually sell some other parts and get your money back).

    Here are some posts discussing it:

    https://technicskeyboards.com/technics-keyboards/technics-kn901-keyboard/

    https://technicskn7000.com/kn7000-forums/technics-organs-forum/ga3-problem/

    https://technicskeyboards.com/technics-keyboards-forum/technics-pr40-some-notes-louder-others/

    https://technicskeyboards.com/technics-keyboards-forum/remove-cover-kn2000/

    I remember our John Dawson (jd5live if you are searching) came up with a way of cleaning and renovating them that he described in the forums. I haven’t been able to find that one. However, John is recovering from a stroke at the moment so can’t help. I’ve tried renovating contacts myself and utterly failed, I don’t have John’s patience or abilities for that (you should see the incredible models he makes).

    And here is a shop where you might be able to get new contacts. I have no idea whether they are any good.

    https://www.synth-parts.com/en/

    Let us know how you go!

    Good luck!
    Mike

    If architecture is frozen music then music must be liquid architecture. Quincy Jones

    mschenkelberg
    Participant
    Post count: 4

    Thanks for all the links,

     

    this weekend i  tried to fix my rubber contacts with a repair fluid for remote control rubber switches. Sadly this did not have a good effect. Some keys are doing better now, some keys are doing nothing anymore. This is a realy frustrating problem.

    After that i did use a soft pencil on the pads on the circuit board which helped to get some of the dead keys to work again.

    Everything else is fine with my old Piano but about the halve of all keys are having problems.

     

    Does anyone know a source for those technics tubber contacts?   (Model  sx-px 74)

    Thanks

     

     

     

     

    Admin
    Keymaster
    Post count: 68

    I’m fairly sure that there aren’t many different types of these contacts so sets from a different model should fit yours.

    The shop I linked you to in the previous message might know (looks expensive though).

    If you aren’t able to contact Dave (he might have spares), do a Google search for Mike Barden who can probably supply them.

    What I would do in your place is to find the model number of the contact strips (should be in the Service Manual) and then look at other Service Manuals to see which instruments have the same contacts. You could then look out for a cheap instrument on Ebay to get those contacts from, or one that isn’t working. The contacts last fairly well usually. While I had problems with contacts before as I mentioned, I was probably playing the instrument 8 hours a day in semi-outdoor environments, and fairly heavy-handed.

    If architecture is frozen music then music must be liquid architecture. Quincy Jones

    mschenkelberg
    Participant
    Post count: 4

    Hi, thanks for your support.

     

    For the moment i disabled the dynamic completly by disabling the second contact on the electronics board so my son can use ist to learn christmas songs 😉

    The Shop was not able to help me and you are right it is expensive to replace all rubber contacts.

    We will try to get a new Piano for Christmas.

     

    Thank you

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