There are three boards (not including the motherboard) that are required to have a functioning Digital Group system: the CPU board, the TV/Cassette Board, and the I/O board.  A memory board is not required as there is already 2K of memory on the CPU card.

Being that the I/O card’s job is to move things around between the other cards, not having one means no system.  Luckily as mentioned in the previous post, the seller realized their mistake in leaving mine out and were willing to send the replacement without fuss.  Phew.  Here’s a pic of it after getting it running:

I was of course hopeful that the system would just magically work when I plugged it in.  Nope.  Instead I got the dreaded Screen ‘O Blocks.  Now what?

One thing I’ve learned to do with vintage computers is Read The Freaking Manual.  At least, when a manual is available.  Thanks to Bryan’s awesome Byte Collector site, I was able to figure out that the card had one of its 74100N ICs in the wrong port.. over on the right rather than left.  When I put that in, suddenly I had a different screen:

Hey.. it’s a result.  I bet that’s the first time this thing has coughed up recognizable characters in eons!