Extender card coming to me thanks to a gift from the Datamuseum of Denmark

 EXTENDER CARD VALUE

The Documation readers house their logic in a metal card cage that has slots to hold up to six PCBs, although most machines are shipped with just four used. Each PCB has two sets of contacts. Each set is double sided, with 18 across the top and 18 just below them on the bottom side. 

The set of contacts on the right, when looking from the rear of the reader, share common signals that are routed up and down to all six card positions. The connectors are soldered onto a vertical PCB called a motherboard in the documentation. The left set of contacts have discrete wires that are specific to the function of each PCB. 

For example, the Control card has the twelve phototransistor signals wired to its left side connector, provides the latched card data to the external connection from that left side connector, and generates the OneDark and OneLight signals on the right (motherboard) connector. 

Each PCB has 36 chip positions although most boards have a few open positions. An average chip is 14 pins each of which may be of interest when troubleshooting the PCB. Because the four PCBs are close together in the card cage, it is very difficult to get a clip to stay on a pin and nearly impossible to reach in with problems while the boards are mounted and working.

An extender card has the two sets of 36 contacts on one and two 36 contact connectors on the other end. It plugs into the card cage and the PCB in turn plugs into the extender. Because of the length of the extender card, the entire PCB is sitting outside the card cage and can easily be probed or connected to. 

OFFER AND SHIPMENT FROM A FELLOW TECHNOLOGIST

I was contacted by a fellow vintage technologist who built extender cards while working on a Model 200 reader in the collection of the Datamuseum in Denmark. Because PCB fabs require a minimum order, they had extra boards, without components installed. They kindly offered to ship one to me, which I gratefully accepted. 

Because the cost was the same, my benefactor put two in an envelope and has mailed them to me. I look forward to receiving these boards, soldering on my spare connectors, then make use of my extender for any diagnostic work on the card readers.