IDing a mystery vintage digital card - Page 1
Forum section: electronics / general

author: D Straney
author_rank: Frequent Contributor
timestamp: November 10, 2023, 03:03:10 pm
content: Just wondering if anyone recognized the card from the attached images. Some points:UNIVAC and CDC systems seem to have connectors rather than using gold fingers on the board; I've seen photos of DEC and IBM cards with gold fingers but nothing yet that looks quite like thisNo search results for "CM305" written on the frontThe flatpack ICs are quad NAND gates, from Fairchild's µDTL family, with what looks like 1969 date codes.It's definitely nothing high-performance, as there was faster stuff than DTL by then, so I'd guess it's not from a mainframe or even the actual processing logic. It also doesn't look like anything aerospace/military (like my CP-901 card), which would justify the older tech but would have more considerations for conduction cooling. So, I haven't traced out the schematic yet, but from the way it combines discrete transistors/passives and ICs, I'm guessing it's meant to drive some kind of load, either core memory or as part of a peripheral device, or something like that.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 10, 2023, 03:22:08 pm
content: Looks a lot like this:https://rcsri.org/collection/honeywell-316/

author: D Straney
author_rank: Frequent Contributor
timestamp: November 10, 2023, 04:06:53 pm
content: Awesome, good find, yes that's almost definitely it! Industrial control makes sense as an application: doesn't need raw processing power, so non-bleeding-edge is fine, but just needs to be proven and reliable but without all the aerospace-level environmental robustness.Pretty sure this is a relay or other load driver. The circuitry is arranged as 8 Darlingtons, with a 100Ω resistor across the lower base-emitter, with the collectors broken out separately and the emitters tied to 2 common power grounds (one for each side). Each collector (/output) has a catch diode to another common point, which is probably the load power supply. The NAND gates are essentially used as inverters, with one input left floating (which is equivalent to a high input - see gate schematic attached). Darlington bases are directly driven by the gate outputs. Each output is driven by 2 NAND-gates-as-inverters with their outputs connected together (specifically recommended by the datasheet, and works because of the open-collector-and-pull-up config. of the outputs): one gate input goes to a unique pin (the control input), and the other gate input goes to a common pin.At first I thought this common input was a lamp-test input that would unconditionally enable all the outputs, but realized I was being thrown off by the datasheet's "wired-OR" description of connecting gate outputs together, when it's really more like a "wired-AND" - either gate can pull the shared output low and keep the Darlington off. So instead, this common input looks like a global enable that allows the individual outputs to be enabled separately.The yellow cap in the lower-left is for filtering on the logic power supply. The 4 blue caps are weird though: they connect to 4 individual pins on one side (and nothing else), and to the power grounds on the other side.

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 10, 2023, 04:16:09 pm
content: You can see a few CM305 boards in the pictures and according to the description they are part of the magnetic core control. Looks like the complete thing is what was later called a PLC.