A420/1 Character repeat issue

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
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carcher
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A420/1 Character repeat issue

Post by carcher » Wed Aug 14, 2019 9:37 pm

Hi,
I am trying to get my A420/1 running and it has a problem with the keyboard input, but I don't think it is a fault with the keyboard. I have replaced the battery holder. It has 4Mb of RAM, an Econet module, ARM2 and RiscOS 3.1.
Have done a DELETE power on and I get the red border and is has reset the CMOS (so the machine can detect the keypress at boot time). It boots fine into RiscOS 3.1. F12 on the keyboard does not work - I am unable to type anything. The Num lock light comes on at boot but after boot I cannot change caps lock or num lock.

When I run !Edit and open a new text window, the machine is continually typing the "/" character as if the key is held down. If I then unplug the keyboard the /////////////////////////////// keeps going, so I think it must be a fault on the main board.
When I power on the machine with out the keyboard - it detects the missing keyboard.
I have searched the 32bit hardware board and read through the fault finding list but I cannot see anything similar.
Has anyone encountered this fault before - or something similar?

Thanks,
Chris

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IanS
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Re: A420/1 Character repeat issue

Post by IanS » Wed Aug 14, 2019 9:46 pm

I can't think of anything that could cause this other than a keyboard fault.

If I hold "/" and NumLock down on my keyboard and power on my A440, I get exactly the behaviour you describe. F12 doesn't work, ////// apears in an edit window and continues if the keyboard is unplugged.

Edit: The Arc keyboard is a serial connection. Most (all?) serial keyboards work on the basis of sending change events, so key down, key up etc. So the machine has seen a key down event for one or more keys at power-on, It never sees a key up event even with the keyboard disconnected.
Last edited by IanS on Wed Aug 14, 2019 11:09 pm, edited 1 time in total.

cmj6502
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Re: A420/1 Character repeat issue

Post by cmj6502 » Thu Aug 15, 2019 9:13 am

It sounds like a keyboard fault. IIRC the A-series keyboards are a membrane type thing which connects to the keyboard controller. Could there be something shorting out to make it think the key is always pressed?

I am not sure if disconnecting the keyboard membrane would help isolate the problem. i think if you do that the computer will still 'see' the keyboard but the keyboard controller will never see any keys pressed. If the problem persisted I would guess a fault in the keyboard controller itself.

I'll leave someone more knowledgeable to say if that's a sensible course of action or not :)

carcher
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Re: A420/1 Character repeat issue

Post by carcher » Thu Aug 15, 2019 10:42 am

Ok thanks - I will dismantle the keyboard and check. I thought it might not be the keyboard as I expected a stuck key fault to stop when I unlpugged the keyboard.

carcher
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Re: A420/1 Character repeat issue

Post by carcher » Sat Aug 17, 2019 9:29 pm

Thank-you - absolutely correct! I dismantled the keyboard and unclipped the black back plastic cover to reveal the membrane circuit. No obvious spills or dirt other than some fluff. I blew away the fluff and gave it a wipe down with IPA on kitchen roll. Reassembled and all working fine.

Many thanks for the help. Now onto that dead Kalok 20Mb HDD!

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IanS
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Re: A420/1 Character repeat issue

Post by IanS » Sat Aug 17, 2019 9:35 pm

carcher wrote:
Sat Aug 17, 2019 9:29 pm
Many thanks for the help. Now onto that dead Kalok 20Mb HDD!
Removing the fluff and a wipe down with IPA is unlikely to help with that :wink:

I can do you a modern(ish) replacement - viewtopic.php?f=8&t=16877

Paul
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Re: A420/1 Character repeat issue

Post by Paul » Sun Aug 18, 2019 8:17 am

I'm happy to thoroughly recommend Ian's IDE boards! :)
Paul.

cmj6502
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Re: A420/1 Character repeat issue

Post by cmj6502 » Wed Aug 28, 2019 12:56 pm

carcher wrote:
Sat Aug 17, 2019 9:29 pm
Thank-you - absolutely correct! I dismantled the keyboard and unclipped the black back plastic cover to reveal the membrane circuit. No obvious spills or dirt other than some fluff. I blew away the fluff and gave it a wipe down with IPA on kitchen roll. Reassembled and all working fine.

Many thanks for the help. Now onto that dead Kalok 20Mb HDD!
Not recommended at all, but I once managed to get a non-spinning ST506 type disc to spin by taking the cover off and spinning it by hand (touching the spindle not the disc) which was enough to get it going then the motor could manage to keep it spinning.

I (very) quickly copied everything off!

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