First I need a card frame to slot my Interak cards into, a backplane and a suitable PSU. I thought I'd found something usable in an eBay job-lot of surplus comms kit, but it wasn't quite as straightforward as I hoped...

My sub-rack came with nice dual redundant PSUs, which looked great but sadly only output +/- 14.5V. An Interak needs (mostly) +5V, and occasionally +/-12V too. I thought briefly about keeping the existing power supplies and regulating the voltage, but as only two rails were wired for redundancy (and I wanted three) there seemed little point. I junked the existing SMPS and fitted another of the same size but with correct voltages to one of the plug in PSU cards. I took the opportunity to fuse the individual supplies at the same time, as I'm planning to add crowbar protection later. Only fitting one PSU card has the bonus of leaving space for floppy drives at the other end of the card frame too.

I was fortunate to find an original Interak backplane on eBay. It looks to be in good condition, other than it needed a haircut on the track-side. Whoever mounted the edge connectors didn't put the most care into trimming the leads - no doubt fine when it was safely mounted in a rack, but 40 years of storage has bent the legs, some almost shorting together.

But how does the backplane mount? The 'new' backplanes on sale today are larger and drilled with fixing holes but mine has nothing like that. 

My first question to the Interak community soon yielded the answer - I need edge connector fixing brackets. The only problem there is they seem to be obsolete and unobtainable! By sheer luck I found three old edge connectors on eBay that still had them fitted, which has at least allowed me to trial fit the backplane. Beyond that I'll probably need to manufacture them.

Things are looking good. But do the cards fit? Erm, No! It seems this card frame wasn't made for the 4.5" x 8" International Size Cards that the Interak uses. 

The fix was to remove the top and bottom rails and then remove about a 1 mm of thickness from each. Success, the cards now fit the opening.

Things are looking good again, I just need to fit the guide rails and the case is all done. 

Wait a minute, is the card bowing out the case? Yes it is! With the guide rails fitted there's insufficient clearance again. That isn't going to work. Cards might fit (snugly) in the middle of the rack but the ends of the case are unusable. The easiest option would seem to be to re-profile the guide rails so they sit lower in the card frame.

That works. I'm just not looking forward to filing-down another 25! Maybe re-profiling a pair at a time as I progress to the next card will be ok though.

Now the card frame really is finished. Time to move on to the actual cards.