Xerox 820-II troubleshooting - need advice

Steven Hirsch snhirsch at
Fri Apr 24 16:56:48 CDT 2009

I purchased an 820-II from eBay, but the seller did a horrible packing job 
and it arrived with the case completely smashed.

Incredibly enough, the CRT was not shattered and once I diassembled it and 
spread things out, it nominally fires up.  I get the monitor sign-on and a 
beep, but no keyboard response at all.

I've already tried reseating everything on the system board and fixed a 
bad solder joint on the crystal for the keyboard MPU.  No luck.

I have some schematics from the web, but they are extremely fuzzy and hard 
to read.  Can anyone help with theory of operation for an 820 keyboard? 
I gather that it's a parallel data interface, but past that I'm a bit in 
the dark.

I should mention that I'm running without a disk drive.  The seller "lost" 
it and I have the carcass of another on the way from a kind cctech group 
member.  Still, I would think there'd be some response to keyboard input 
without the drive on line.



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