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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: koaftder on June 08, 2008, 06:55:41 PM

Title: a3k keyboard problems
Post by: koaftder on June 08, 2008, 06:55:41 PM

I have an a3000d with a keyboard issue. I have the same results with a Lyra ps/2 adaptor and a commodore amiga branded keyboard with the large DIN style connector. With the system powered off for an hour or two I get keyboard input. Anywhere from 10 seconds to 10 minutes it starts sporadically dropping keys and repeating letters then stops working all together.

CTRL+AMIGA+AMIGA always resets the machine despite not being able to respond to keyboard events. I suspected the CIA could be a problem and since I have two on my system I swapped them, same problem. I have another pair of CIA chips which I tried and still get the same problem. With the keyboard disconnected the clk and dat lines to the CIA are pulled high as indicated in the schematic. With the keyboard connected the clk line to the CIA is 4.8v and the dat line is 1.2v.

My internal and external floppy interfaces are working properly.

So far I have confirmed the following:
1) My keyboards are in good working order
2) The CIA chips are in good working order
3) The pullups are in spec
4) No bad traces from the KB physical interface to the CIA

Any tips on where to proceed from here? Is there any specific documentation floating around about how the CIA works? Upon receiving a keyboard event, does INT2 fire off?

Title: Re: a3k keyboard problems
Post by: Zac67 on June 08, 2008, 07:17:04 PM

Have you checked voltage at the PSU plug, on the KB connector and/or inside the keyboard?

Title: Re: a3k keyboard problems
Post by: da9000 on June 08, 2008, 08:56:36 PM

Hey Koafter,

due to your explanations I'd be included to say it has to do with overheating or something. Could it be the PALs/GALs which are near the ChipRAM? Put a fan on them and see if you see any difference?

Good luck!

Title: Re: a3k keyboard problems
Post by: rkauer on June 08, 2008, 09:50:47 PM

 I bet on a PSU becomes to fault.

 Use an AT/ATX hack and re-set jumper J350 to EXT position (2-3) or build a "tick generator" (schematics on aminet).

 Also check for gunk on kb connector.

Title: Re: a3k keyboard problems
Post by: koaftder on June 08, 2008, 10:22:20 PM

Thanks for the tips guys. I have good power to the KB interface and no corrosion/gunk in the sockets. I have less than one ohm of resistance from the clk and dat lines on the kb interface to the CIA.

I'm using an ATX powersupply on the a3k and have it set for vsync on jp350.

Title: Re: a3k keyboard problems
Post by: koaftder on June 08, 2008, 10:26:05 PM

I have also chilled each chip on the mobo while fired up with a can of compressed air upside down and still no kb capability after running for a minute or so. ):

Title: Re: a3k keyboard problems
Post by: koaftder on June 08, 2008, 11:48:53 PM

my tic signal from vsync is 190us in width with ~16.5ms spacing in between upon startup. As the machine warms up it gets erratic and I loose kb functionality.

Title: Re: a3k keyboard problems
Post by: Zac67 on June 09, 2008, 07:28:50 AM

Very strange...

Try to reseat Agnus (careful with that socket) and check voltage level on its socket.