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Old 20 January 2011, 09:13   #1
Dougal
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Amiga 500 slight keyboard issue

I recently bought an A500 at a carboot sale. I know i have loads of them, but i couldn't resist

Anyways, on the whole it works fine, has no problems at all booting up and runs software/games perfectly.

The only issues i have are with the keyboard.

For some reason the "0" (Zero) keys on both the main keyboard and also the keypad just simply refuse to work.

Also the CAPS light does not light up, but CAPS does work.

Now if it were one of the "0" keys not working i would have put it down to a dodgy key or something, but it is BOTH "0" keys not working whilst the rest of the keyboard works fine.

Someone on another site suggested that there might be a connection issue, but I dont really know where to start. Could there be something more specific that i can look at on the Keyboard ?
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Old 20 January 2011, 10:13   #2
chiark
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Dougal, the caps light not working will be down to the membrane deteriorating, probably on the right hand edge of the keyboard membrane IIRC. If you trace the circuit you'll see power for the LED comes from the very edge, and it's the first bit to get damaged.

Happened to one of my 4000 keyboards which has the same membrane as the A500 single keyboard membrane...

0 issue is probably a membrane issue too. Have a look on ebay for replacement membranes.
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Old 20 January 2011, 10:20   #3
Dougal
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Quote:
Originally Posted by chiark View Post
Dougal, the caps light not working will be down to the membrane deteriorating, probably on the right hand edge of the keyboard membrane IIRC. If you trace the circuit you'll see power for the LED comes from the very edge, and it's the first bit to get damaged.

Happened to one of my 4000 keyboards which has the same membrane as the A500 single keyboard membrane...

0 issue is probably a membrane issue too. Have a look on ebay for replacement membranes.
Hmmm, i'll take it apart and have a look later on. Thanks
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Old 20 January 2011, 11:50   #4
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You're welcome - good luck! I fixed mine with some conductive paint...
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Old 20 January 2011, 13:08   #5
Dougal
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I looked at the membrane and it looks "ok", as in the print is all there, but from the top i did notice one of the traces a little darker than the rest but other than that it looks in great shape.
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Old 20 January 2011, 13:49   #6
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Damn. Well, I think that just proves I don't know what I'm talking about

I think that the caps lock signal can be traced all the way back to the membrane connector - can you check continuity on that?
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Old 20 January 2011, 14:34   #7
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I agree that its usually the membrane.
however, another common problem is a piece of plastic under the little PCB.
in time it can get pierced with sharp pins and short-circuit with the RF shielding. so check that, too.
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Old 20 January 2011, 14:49   #8
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It is very rare to see a broken membrane in an A500 keyboard, unless the keyboard has suffered liquid damage which has corroded the traces, but this is usually very easy to see.

The most common faults with these Mitsumi keyboards are the black rubber contacts under the keystems, they get dusty and they become polished.

Wipe the membrane with a moist cloth, be sure to dry it meticulously afterwards.

Then take a piece of copier paper (out of your printer, an old envelope or bill that came in the mail, something), fold it a couple of times to get rid of the sharp edges and then just press the non-working key and wipe the rubber contact a couple of times with the paper until it is no longer shiny. (naturally you have dismantled the keyboard to do these procedures)
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Old 20 January 2011, 18:13   #9
Dougal
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I did dismantle the keyboard and i gave the membrane a quick clean as there was quite a bit of dust but no gunk or anything like that. Also i looked at the plastic cover that protects the keyboards small pcb from shorting with the rf shield and that looks 100% fine too.

I also unplugged the membrane from the pcb keyboard controller and refitted it.

Is there a possibility that the actual pcb controller has a problem? Could it be a chip in the Amiga or kickstart?
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Old 20 January 2011, 21:45   #10
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If you get any keypresses through at all, then the Amiga itself is fine.
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Old 23 January 2011, 08:00   #11
Dougal
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I noticed the "P" key and one of the "/" keys i think does not work either.

I think i have a spare A500 keyboard at my mums. I hope
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