ISA Riser 8 bit for Olivetti PC1 and other XT computers

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Motivation and overview

This project is about an ISA riser card for the Prodest Olivetti PC1 personal computer but it may very well work with other old XT style computers with a regular 8 bit ISA slot!

They can be ordered online at dirtypcbs.com if you are interested in getting one.

 

Schematic

The circuit is 1:1 for every pin in the original ISA slot being expanded to the two slots on this card. The only components are four 100uF/16V electrolytic capacitors near the slots.

schematic

PCB

The following pictures show the top and bottom layers of the PCB.

top view  bottom view (mirrored)

 

It has been brought to my attention that I forgot to enlarge the tracks for B5, B7 and B9 (-5V, -12V and +12V) and that they are not thick enough to carry currents in excess of 100mA without starting to heat up. This can be a problem when connecting ISA cards that draw high current from those lines.

However we also need to remember that the PC1 does not provide power on B5 and B7 (-5V and -12V respectively) so this is only a problem if you use a card that requires +12V from B9 and internally regulates it to whatever voltages it needs. If you really need to draw a lot of current from B9 (+12V) you can solder a small wire from the pad to the pin of the socket as a last resort solution.

 

Software

N/A

Prototype

N/A

Pictures and Videos

bare riser pcbs to be assembled isa sockets pcb partially assembled

riser on pc1 closeup to riser and XT-CF board

 

Downloads

You can order this board yourself at dirtypcbs.com

 

References

  1. Old computers page here at www.enide.net
  2. The Olivetti Prodest PC1 page by John Elliott
  3. Olivetti Prodest PC1 facebook page
  4. TI-99 Italian User Club - Olivetti PC1 - The one page

 

Published on Tuesday 2016/11/08, last modified on Monday 2017/05/15