Sun 4/330 revisited...

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. So, it looks like bit 6 of the bus is fine *except* when a serial port access is in progress (i.e. other things sharing that bus are being accessed fine) Three possibilities at the moment: 1) The big LSI Logic L1A3626 IC which appears to control the serial port bus is broken internally. 2) Something upstream of the LSI Logic chip is faulty. 3) Something else on the board is responsible for driving the bus during SCC ops, and there's a break in the bit 6 track to it somewhere, resulting in it always floating high during serial access. I can't do much about 1 and 2 without knowing the pinouts of the LSI chip or having full schematics of the board :-( Point 3 I can test by tracing one of the other data bus lines and seeing if it goes anywhere that line #6 doesn't. I had a look at our Sparc 1 and 2 machines, but they don't use the same chipset. They do however have a similar IC to the LSI chip in the 4/330 marked as "buffer" which of course increases suspicion that the LSI chip in the 4/330 - or something upstream of it - has broken. Chances are I'll be looking for a new board (yeah, right!) given the lack of schematics. Other alternative would be to find a framebuffer board for the machine and then use a graphical console - it might be easier to find a compatible framebuffer versus a whole new 4/330 board... Grumble! cheers Jules