Working on ways to manufacture SLT card sockets and SLT board receptacles

IBM SLT SYSTEM USES .125" PITCH PIN SEPARATION IN A GRID ON THE BOARD

The board is divided vertically and horizontally in 1/8" steps, with a hole drilled in the intersection of each horizontal and vertical step On the board (IBM's name for a backplane) a gold plated pin is inserted through the hole at specific locations to form the pattern of 2 rows of 12 pins each where an SLT card can be inserted. 

Black dots are pins

The SLT board is organized with each card slot consisting of 14 vertical steps 1-14 and five horizontal steps A-E. An SLT card has pins that fit into rows 2 to 13, in columns B and D. Thus the spacing is .125" between pins in a row and .25" between rows. I haven't found an IBM published diameter for the pin, so I will have to measure one at my workshop. 

On the card, springy contacts are soldered onto the PCB and are pushed toward the board by the pins of the SLT board as the card is inserted. There is a molded black plastic housing around the contacts at the end of the SLT card. 


I can 3D print the contact housings. I can have PCBs manufactured with the .125" spacing holes to form a receptacle. A small challenge is to find a source of suitable pins I can solder into the board. I would use a junk SLT card as an aligner for the pins while I soldered them from the back of my PCB. 

The bigger challenge is getting the springy contact just right - too much pressure and it could damage the SLT board pins, too little pressure and a reliable contact is not made. I have used RF shielding contacts for similar tasks. Harwin RFI Shield Fingers, part S7091-42R, surface mount parts that solder onto a PCB pad. 

They stand .106 inch above the PCB and a normal PCB is .063" thick. That puts the two ends at .275" while the SLT board pins are .25" apart. These are .0985" wide and the spacing between pins in a row is just .125" I would have to carefully solder them to avoid shorts. 

Connor Krukosky had discovered an Amphenol ModU receptacle that has the correct pin spacing in both rows and columns. There are a variety of contacts to insert in the header for different wire sizes and surface treatments. 

ORDERED PARTS TO EXPERIMENT WITH THE CONTACTS AND AMPHENOL HEADERS

I ordered a couple of the ModU headers with the contacts designed for .012" diameter pins, gold plated and appropriate for my 30 gauge wire wrap leads. I would need a different size wire for cabling.  

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