Ohio Scientific

	CD-23 Disk System Repair Part 1 Bring-up, testing, and repair of an OSI CD-23 hard disk system with Shugart SA-4008 14 inch Winchester disk at the System Source July 2023 workshop.
	Ohio Scientific 400 Superboard Build This is actually the second original blank Ohio Scientific 400 Superboard I've had, but the first I've built. After scanning for reproduction, this 400 board was built up for testing some interesting processors a friend had. Parts choices were made to give a vintage look to this modern build.
	Repairing an OSI 470 Floppy Controller and Building a Second Challenger III This project started out as a repair job to get an OSI 470 floppy controller working, and resulted in putting together a second Challenger III system from parts! This particular floppy controller had some very weird problems.
	A Universal RAM Board for OSI, GW-OSI-RAM1 A common issue when restoring, repairing, or building up an Ohio Scientific system is a lack of dense, reliable RAM. OSI boards do exist that provide 64K of static RAM on a single low-power board, but these are rare. There are even fewer options if you want 12-bit support for the 560Z Processor Lab in PDP-8 mode. With two prototype RAM boards built, I decided to lay out a universal OSI RAM board to meet the needs of as many OSI systems as possible.
	The OSI 560Z Processor Lab The Ohio Scientific 560Z "Processor Lab" is an unusual coprocessor board for the OSI bus -- it allows interfacing a Z80 and IM-6100 PDP-8 on a chip and controlling them with the 6502 through a driver package. This package not only allows you to load and examine memory for the coprocessor(s), but also controls timing, single-stepping, slow stepping, and I/O emulation. It's a very rare board, with only one known functional board in existence, until now!
	Expanding to a 64K RAM Board The 32K RAM board project was built with expansion in mind. Here we expand it to 64K with another 32K x 8 static RAM using the same 4K segment selection as the 32K board. Provisions for memory management allow for expansion beyond 64K using Ohio Scientific's memory management strategy.
	Building a 32K RAM Board With a quantity of 495 prototype boards in hand, it was time to build up a RAM board for the Challenger III. My implementation uses a single 32K x 8 static RAM in DIP packaging, which is split up into eight 4K segments, each of which can be enabled or disabled individually. It's also expandable to 64K and beyond due to a few design decisions.
	Cloning the OSI 495 Prototype Board The Ohio Scientific bus is pretty easy to interface with, except prototype boards are hard to find! Chunks of perfboard large enough are expensive, the insertion/extraction force of the Molex KK-156 connectors required soldered connections, and Ohio Scientific's 495 protoboard is unobtainium. When I finally found an OSI 495 board, I decided to clone it.
	Cleaning up the Challenger III I've had a Challenger III for a few years and apparently never documented it! I pulled it out this week to work on an OSI related project only to find it was in bad need of a cleaning. I fixed a few problems along the way. It's now back up and running with a 510 triple CPU board and 48K of RAM.