Sun 4/330 revisited...

[Tony Duell]

> 
> 
> Right. It's *not* the 8530 SCC chip that's faulty, but it's *not* the
> data bus either - there's plenty of bus activity so bit 6 isn't
> permanently jammed high.
> 
> After checking the bus, I replaced the SCC chip with a socket and tried
> my spare SCC chip from home (remarkably easy job as it turned out) -
> gave exactly the same results on the console.


First thought : There's some other device -- maybe soemthing like an 
interrupt vector source buffer -- that's being enabled along with the 
Z8530. Of course this might be inside that LSI chip you mention.

> I can't do much about 1 and 2 without knowing the pinouts of the LSI
> chip or having full schematics of the board :-(

Well, there's a winter-evening project for you -- draw out the 
schematics. 

-tony