Date   : Tue, 12 May 2009 16:12:00 +0100
From   : mike@... (Mike Tomlinson)
Subject: BBC B+ Econet weirdness

In article <89056F0D6B620444BE8677A5802EE49F081B9D5F@...
1.systemhost.net>, michael.firth@... writes

>Having had a look at the B+ service manual, there is a 4.5s timeout on
>attempting to send a packet, so I think if it doesn't error out before
>this then the hardware will lock up.
>I've certainly left it 60s+ and it doesn't return. Escape doesn't work
>either, Break is needed to release the lockup.

Possibly suggests an interrupt problem or slow/dicky RST- line. As
you've said you have replaced the 68B54, if there's a circuit on the B+
taking INT- from the 68B54 through to the 6502 (I seem to remember it's
not straightforward), I'd be looking at that.

You are sure the Econet spine is in good order and has good termination?
Does the machine still hang if you unplug the net and press Break a few
times?

>As I said elsewhere in the message, until yesterday the machine had been
>running fine on Econet for several weeks, which I think would rule out any
>incorrect fitting problems (but not a component going faulty)

Agreed.

>The machine in question is a B+, not a B.

Sorry, didn't read your original post properly! Hadn't had enough
coffee...

> The B+ has space on the
>PCB for collision detection, but, quoting the service manual "the
>collision detect circuitry is not fitted because the software protocols
>should prevent any collision"

I'd definitely fit it.

> (I say 'user machines', because I think the
>Filestores had clock generation)

They do.

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