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Old 15 February 2020, 01:51   #1
RincewindUK
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Ctrl key not working on A500

Hi,

I’ve just picked up an A500 Rev 6 and a few of the keys weren’t working. I’ve cleaned up the membrane and everything’s working find now except for the Ctrl key (a pretty important one!)

I’ve checked and there doesn’t appear to be any breaks in the membrane paths, and both pads have continuity to pin 32 on the keyboard controller chip so I’m very confused. I get nothing in Keir’s keyboard test if I short the pads manually.

Any ideas? I’d hate to have to buy a new membrane for one key!

Thanks,
Mike
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Old 15 February 2020, 04:38   #2
RincewindUK
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Ok, progress of a sort. After some fiddling all keys now work but Ctrl+A+A doesn’t work to cause a reset. In Keif’s self test, if I press Ctrl and left Amiga, as soon as I press right Amiga the Ctrl key goes off. And in Workbench or anything it’s not triggering a reset. Is the keyboard goosed?
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Old 17 February 2020, 13:31   #3
solarmon
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There is a 555 reset circuit on the keyboard that may be failing - there are a couple of caps of there that could be replaced.

There are two situations where the keyboard sends a reset signal to the Amiga 500:

1. On keyboard power up.
2. On the detection of CTRL-Amiga-Amiga key combo.

You can do the following trick to see if the reset circuit is working. Without the keyboard connected, power on the Amiga 500 to the kickstart screen. Now plug in the keyboard. This should initiate a reset (as per option 1 above) signal and the Amiga 500 should reset/reboot itself.
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Old 18 February 2020, 01:53   #4
RincewindUK
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Thanks for the suggestion.

I feel like such a n00b - it turns out the membrane connector just needed reseating! I was wracking my brain trying to fix it, testing continuity on the membrane and even shorting pins on Gary to make sure the system would reset. Then in a moment of clarity I just pulled down the membrane connector, reseated the connector and tried it and it all suddenly sprang to life!

There's a lesson here that sometime the simplest solution is the right one! At least it all working now...

Thanks,
Mike
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Old 18 February 2020, 05:15   #5
aeberbach
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Sounds right - most of the "special" keys have a dedicated circuit unlike the rows and column arrangement of the regular keys. That one key's circuit wasn't connected right.
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