30117Get a board Xerox 820-II working fine
- Mar 24, 2013Hello everyone,
I got a board Xerox 820-II without any other components and without disk controller.
After changing the video sync and created a composite video on video i have the correct prompt.
I made a keyboard interface to convert a PS2 keyboard in parallel with the same schematic that works well with my Ferguson Bigboard I and the other card Xerox 820-I.
I saw that on the xerox 820-II board there are almost 2 ICs with the name Signetics 3341PC (U102 and U101) that are between the U65 (system and Keyboard PIO) and the 72LS74 (U96 and U97) that come to connect to the keyboard input (see sheet 7 of thsi schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf).
I come to requests:
1) The keyboard does not write. I read on a post that I can not find anymore that without the inclusion of the disk controller card into its slot the keyboard would not write.
Perhaps because there is not anymore the continuity of the chain interrupt (see at the bottom of sheet 8 close to U65 into this schematic http://bitsavers.trailing-edge.com/pdf/xerox/820-II/Xerox820-II_Schematics.pdf )?
2) If i not find the disk controller card I was thinking about to self-build it on a bareboard hoping that the diagram at the bottom of the last pages at http://bitsavers.trailing-edge.com/pdf/xerox/820/Xerox820_ServiceMan.pdf is accurate. Where can I find a card edge connector male 72-pin 2.54mm pitch?
3) You also have some suggestions for me?
Thanks so much
Enrico Pisa (Italy)
PS: This board not have 2 ICs just on the central http://cgi.ebay.it/ws/eBayISAPI.dll?VISuperSize&item=290885192545
This one has 2 ICs U101 and U102 in the same postions http://www.ebay.com/itm/Xerox-820-II-Motherboard-Z80A-CPU-/150617117645?ViewItem=&item=150617117645&lgeo=1&vectorid=229466&nma=true&si=7VCHVvqGfhDvXOhHABsDRVUKnNY%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557 no info on ist schematic about this differenze of ist release
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