Date   : Sat, 11 Feb 2006 22:00:49 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: B+ 64k won't respond to keyboard, Econet fitted

"neil f" <faz@...> wrote:

>> Therefore the system 6522 is functioning.  Do you have sound
>> - does Ctrl-Break give a beep?  If yes, does Ctrl-G give a beep?
>
> Ctrl/Break doesn't beep. Ctrl/G doesn't beep. The machine beeps at
> switch-on but only the lower tone, not the higher of the two tones
> (this is with no secondary ROMs installed, to ensure Econet is not a
> factor). Interestingly, after it has been on for about an hour or so,
> the machine beeps once. Does it every time it's left on.

It all points to what I suggested earlier, a failure of the system 6522 VIA 
to cause interrupts in the CPU. (The 6522 generates the 100-per-second timer 
interrupts.) If this failed then the beeps would not work, and keypresses 
will not get entered into the keyboard buffer. (The first part of the 
two-tone switch-on sound is just the default noise issued by the sound chip 
before the reset sequence sets up the chip properly. The second part is a 
"proper" beep, the same as VDU7, under timer interrupt control.)

A dry joint or a broken motherboard track (perhaps affecting pin 21 of the 
6522 - the IRQ line) looks the most likely cause to me. If you can find the 
break you could try bridging it.

David Harper