Xerox 820-II troubleshooting - need advice
ard at p850ug1.demon.co.uk
Mon Apr 27 13:15:28 CDT 2009
> Fortunately, it turns out to have been much simpler. The 820-II firmware
> apparently expects the FDC controller to be present during init. To keep
> things simple, I had the daughterboard unplugged.
> Once I smartened up and plugged the controller in, it started responding
> to the keyboard. I can only assume it resets the controller at power up
> and is waiting for some sort of state change or interrupt. Without the
> board present it was just waiting forever and never getting to the stage
> where it would acknowledge character input from the keyboard.
This reminds me in a way of a problem I had with a Whitechapel MG1 (A
32016-based workstation). It flashed the error LED at power-on, reporting
a multi-bit DRAM error.
TO gcut a very long story short, after battling throuhg the memory
arbitration logic, I discovered there was actually nothing wrong. The
mainboard has 512K of RAM on it, the boot ROM needs (and tests) 1.5M.
After plugging in the 2 RAM expansion boards I'd removed 'to keep things
simple' (:-)), it worked fine. This is not documented in any of the
manuals I have.
> Nice when things turn out this easy.
In my case it wasn't so simple. It took me a day to go through and check
all the logic. It's a complcated machine...
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