Keyboard keybed, few dead notes

Discussion in 'The Projects Forum' started by solderboy, Dec 7, 2015.

  1. solderboy

    Thread Starter New Member

    Nov 12, 2014
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    I have an alesis q25 midi keyboard, whose middle c-note first went dead, then upon opening up the unit to clean the rubber contact underneath, and then putting it back together, 2 more notes are dead. I then took it apart again and cleaned the whole rubber strip with rubbing alcohol, and then used a dust blower, as well as cleaned the surface underneath the rubber strip with 91% isopropyl, but the same 3 notes remain dead.

    I can't for the life of me see why a key went dead merely by opening the unit, or the first key for that matter. If a wire was damaged then I think more or all keys would've went dead, I didn't spill anything on it either. I've tried poking the key's contact area with a tool, and pressing the rubber contact with my finger, but there's just nothing, the signal's dead. 3 keys are dead, i see nothing under them such as individual wires or leads, perhaps it's something underneath the rubber strip's surface, but didn't want to go there in case there's nothing, as usually cleaning the rubber contact does the trick.

    If I knew what underlied the key's signal generation all the way to the pcb on the side perhaps I could track it down? Keys dying like flies, for no apparent reason.

    Below are pictures of the inside of the keyboard, of the side of the rubber strip. The first key in view is working btw, the mess on the black key is from sticky tape. Let's see if there's some genius.
     
  2. GopherT

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    Nov 23, 2012
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    With these types of switches, the copper oxidizes a bit or the conductors imbedded in the rubber oxidize or the rubber crumbles a bit and interferes with the contact. Cleaning the rubber with alcohol is ok as long as you don't soak/saturate the rubber with alcohol.

    Any acidic skin oil or other contaminants, even alcohol, can cause some oxidation of the bright copper.

    To get back the clean, bright copper, you can use a decent quality white or pink pencil eraser to polish the copper in the PCB. It doesn't take long with a good eraser. If your eraser isn't doing much, try another brand/style. Bright copper should appear after a few strokes.

    Repeat on the rubber - you may need a small section from an actually pencil to get it all clean. Now, you will not see any progress on the rubber part but you know how much work you needed for the copper, use that experience (number of strokes and pressure) to estimate how much is needed for the rubber.

    Use a vacuum cleaner to remove all traces of the eraser particles.

    Put it back together and play your keyboard.
     
  3. solderboy

    Thread Starter New Member

    Nov 12, 2014
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    Well, that sounds good. Remember, I tried poking the contacts manually, that's how I knew they were dead/dead.

    Shoulda maybe gotten a picture of the surface contact under the rubber, maybe'll do that next, thanks.
     
  4. Kermit2

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    I have seen these type of switches and they sometimes use a graphite/carbon material on the bottom of the rubber portion. Alcohol will destroy this material pretty quick.
    If you cannot short the switch contacts and hear it play a note then look for broken solder joints on the interconnect headers. A thin dark circle or ring in the shiny solder surface is indicative of a broken connection. Reheating the joint will fix it
     
  5. solderboy

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    Nov 12, 2014
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    I'm going to try your advice, then come back if it doesn't work.
     
  6. solderboy

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    Nov 12, 2014
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    Alright, so I followed the eraser advice, but now 4 keys are dead, and I can't tell at all that it was because of this method, or something else.
    It did indeed look like the contact pads (copper?) under the rubber strip did look shinier after rubbing them, so I had hopes there, but trying the keyboard noticed 4 keys, including the same ones as b4 are dead.

    As for interconnect headers, not sure what you meant. I see only ribbon cables, and it's very hard to detect anything with them as the connector pins are so small, and not even sure all of them come lose. But I'd think if twas a ribbon cable, more than 4 random notes would've died.

    It seems alesis dropped the ball on this one. Other keyboards typically only require cleaning out the rubber contacts when keys fail, this thing is beyond, seems more keys fail each time I try to fix it.
     
  7. SLK001

    Well-Known Member

    Nov 29, 2011
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    I believe that the contacts should be GOLD plated. Using an abrasive to clean the contacts will REMOVE the gold, leaving bare copper. Each time you try to fix it, you probably fatigue more wire connections to failure.

    If SHORTING the contacts do NOT play a note, then the KEYS are NOT the problem. You'll have to start troubleshooting elsewhere.
     
  8. mcgyvr

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    Oct 15, 2009
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    More than likely thats exactly the problem.. and its VERY common..
    Your suggestion to short the contacts is exactly what the OP should do to verify that missing conductive material on the rubber pad surface is the issue..
    Then there are products to repair/replace that conductive surface.
    http://www.amazon.com/Chemtronics-Circuit-CW2605-Rubber-Keypad/dp/B002BZK06G

    You can get "crafty" with some photo spray/gold flake too..
     
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  9. Kermit2

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    Oooh, Ahhhh! A good solution to this problem has eluded me my whole life. THIS is why I like the place.

    Consider your idea appropriated, and very much appreciated Sir.
    My thanks to you for solving an old problem for me. :)
     
  10. GopherT

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    Have you tried this? What range of resistance is expected from this?

    Thanks
     
  11. Kermit2

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    Gold on gold or gold on brass would indicate a milliohm resistance range with the normal amount of contact pressure. The carbon type are higher but almost always less than 100 ohms
     
  12. mcgyvr

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    I meant gold foil..
    That super thin gold crap squares that gaudy crafters brush on to a lamp table or picture frame,etc... :D

    It works.. for a while anyways..

    Conductive paint works too.. Aluminum foil,etc...
    The fact is the rubber no longer has enough carbon to be conductive anymore so anything conductive that you can use at the end of that rubber bumper to replace that works..

    Heck I've even superglued a cut off resistor wire over the pad.. anything to bridge the PCB's contact pads
     
  13. solderboy

    Thread Starter New Member

    Nov 12, 2014
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    Thanks for the tips.


    If someone still cares to care, I might upload a pic of the rubber contact surfaces, just in case.

    Just to remind, the keyboard is midi only, so the keys press down the rubber contacts on the contact surface, and generates midi signals only. and I assumed that the pressure itself triggered the signal, but now hear of carbon in the rubber. I may upload a pic of the rubber along with the surface.
     
  14. solderboy

    Thread Starter New Member

    Nov 12, 2014
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    So for completeness here's the rubber contacts and the surface contact/pads, after alcohol and eraser treatments.
    I believe one of the surface pads, perhaps the left most, is one of the dead signals, I for one can't detect anything wrong by looking at it.

    So just in case if anything looks obvious, otherwise I wonder how an electrician would diagnose this.


    The keyboard was less than $50, and doesn't warrant bringing in, but don't want to get a new one if i can fix it. And just need to be sure before investing in any repair item, or if can't be sure, then so be it.
     
    Last edited: Dec 15, 2015
  15. Kermit2

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    Try shorting the contacts with a gold ring or other precious metal jewelry. It seems both sets of contacts are of carbon impregnated rubber, and there is no true metal contact surfaces. Is this the case?
     
  16. mcgyvr

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    You assumed wrong..
    Those are carbon contacts for sure
     
  17. solderboy

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    Nov 12, 2014
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    To me the contacts could be either metal, something that looks like metal, or coated metal, but someone in the thread mentioned copper, and they're copper colored.


    Btw, how do I short the contacts like you mention? Is it done by simply touching them with a piece of jewelry one by one?



    Thanks, other than that, I'll look into adding new conductive as per mcgvr's advice.
     
    Last edited: Dec 17, 2015
  18. mcgyvr

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    You just need to bridge (connect) the 2 oval circuit board pads with something conductive.. paperclip/wire,etc...
     
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  19. solderboy

    Thread Starter New Member

    Nov 12, 2014
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    Update, I tried sticking small thin pieces of aluminum foil onto the dead contacts, then tried it, but it didn't seem to work at all. Not sure if it's because the aluminum pieces didn't stick as well as necessary, or if it's because that wasn't the problem, as suggested above in the thread. (see previously uploaded pics if necessary)

    Might try again, tried using a gentle glue, as opposed to hard super glue.
    Haven't tried shorting the contacts yet, mainly because I'm not sure how to go about. My idea is taking a conductive metal wire and bridge the contacts of the same pad, and repeat for each dead note's pad?
     
  20. GopherT

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    Nov 23, 2012
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    That is the idea. Good luck.
     
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