Fixing dead keys?


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Hi,

I just got an old Proteus MPS Plus Orchestral (it was made at the beginning of the 90's), but there are 2 dead keys (C4 and E4).

I'll probably open the case and see if I can fix it by myself (hoping I won't kill the whole synth in the process)...

Does anybody have some experience of this kind of repair?

Thanks
 
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Follow up:

I carefully disassembled the keyboard, removed the dust and the spider webs inside, cleaned the rubber strips below the keys...and the E key is now working! :)

Still no sound from the C key, though... :(

It's easy to disassemble and reassemble, I'll give it another try later.
 
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That is cool! I'd love to have a look inside mine, but everything works. And then there's that warranty thing.

Next time you crack it open, would you be willing to take some pictures for us to see?
 
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OK! I opened the synth only once, but I had taken some pictures (they could have been useful if I couldn't remember how the reassemble the unit...).

After removing a few screws beneath the keyboard, the three segments of the top cover can be removed. There are two printed circuit boards (PCB): the left one is where we connect the power cord, midi cables and amp cables. The other PCB is located below the buttons and LCD.

http://web.ncf.ca/ch865/keyboard/synth1.JPG

Here's a closeup of the left PCB. We also see dirt on the keys...

http://web.ncf.ca/ch865/keyboard/synth2.JPG

Next, I removed the keys.

http://web.ncf.ca/ch865/keyboard/synth3.JPG

There's 2 little PCBs below the keys, with several identical resistors neatly alligned: there seems to be 2 resistors for each key.

http://web.ncf.ca/ch865/keyboard/synth4.JPG

One of the little PCB has been removed, revealing grey rubber strips. One of these strips had some sticky substance in it, I cleaned it.

http://web.ncf.ca/ch865/keyboard/synth5.JPG

And here's the other side of the removed PCB: when we press a key, the dots on the rubber strips are pressed against the grey rectangles (each grey rectangle accomodates 4 keys). I guess these are some kind of pressure sensors (the keybard has aftertouch).

http://web.ncf.ca/ch865/keyboard/synth6.JPG

As I said before, one of the two defective keys is working again, but not the other. All I did is some cleaning, I didn't even disconnect any electrical connexion. In a few days, I'll borrow a voltmeter (or even an oscilloscope) to see if I can learn something more.

Yesterday, something interesting happened: the synth played a note by itself, while I was not playing: it was the note which should be played when I press the dead key!!!
 
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It works! I repaired my synth!

I had to open one of the "grey rectangles" (by lifting an adhesive tape): inside the rectangle, there are 2 electrical contacts for each note (I think the synth use the delay between them for velocity sensitivity). One of them was sticky and the note remained stuck, so all I had to do was cleaning it.
 
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Thanks a lot ypelletier!
I havejust followed the procedue you described so clearly and fxed my MPS (PROTEUS) keyboard.
A observation, the components you called resistors are actually diodes.
Anyways, very helpful. Thanks to you the keyboard is back. All it takes is removing that tape and cleaning with alcohol the inner part of the contacts of the bad keys.
 
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ypelletier,

Have you ever messed with the control buttons under the hood of your keyboards? I have an XP-50 whose control buutons need to be coaxed (pressed hard) in order to work. I think I'll take her apart this weekend and see what's there. I would really appreciate any recommendations for cleaning solutions or cautions that you could pass along.

Thanks, Pablo
 
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ypelletier,

Have you ever messed with the control buttons under the hood of your keyboards? I have an XP-50 whose control buutons need to be coaxed (pressed hard) in order to work. I think I'll take her apart this weekend and see what's there. I would really appreciate any recommendations for cleaning solutions or cautions that you could pass along.

Thanks, Pablo
Control buttons are just simple menu buttons right? I have taken apart many a video game controller with an eye to fixing them. On an old Nintendo, the plastic buttons generally pressed on a rubber pad which had some kind of electrical conduction on the bottom of it in a circular shape. The PCB would have a circular shaped contact with a split in the middle so when you press the button down the pad completes the circuit. The circuit board and plastic button are relatively invincible, but the rubbery part can get all kinds of problems (sticky if you spill stuff on it, worn out and less springy of it's old, the contact pad on the bottom gets dirty easily and so on). You might be able to clean or replace the pads... or even swap the ones for important buttons with lesson important buttons.
 

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