Ohio Scientific

Model: Ohio Scientific Challenger 4P
Year: 1979
Processor: 6502 @ 2MHz
ROM: 8KB BASIC + OSI Monitor
Video: 64 characters, 32 lines monochrome ASCII w/ extended character set
Sound: Tone generator
OS: OSI BASIC V2 Rev 3.2?

  502 top 502 underside 540 detail 540 oblique 542 detail 542 top back panel left back panel right  

  backplane1 backplane2 backside improved c4p cleaned up keyboard mess of wires nopsu oldpsu  

  on screen overview primer psu improved running again runningbasic screen garbage side view improved  

  side view softwarehaul softwarepages1 tapes top view improved workbench  

My OSI Challenger 4P has had a few things replaced on it since I got it. A few of the 2114 SRAM chips were dead and needed to be swapped out to give it back a full 8K. The power supply was considerably hotter than it should have been, rendering the top of the machine untouchable in about 30 minutes of operation. The internal wiring harnesses were also incredibly messy and sketchy, relying on electrical tape for insulation. The keyboard also had a number of dead switches, which also needed replacement. I took care of the keyboard and RAM problem first, rendering the machine atleast usable. After a chance encounter at VCF West in 2019, I scored a box of OSI stuff, including an A15 backplane PCB. I removed the original wiring, along with the old backplane cover, and stand-alone dsub connectors, in favor of the A15 board and a chassis fan. Oh, and the power supply got replaced with a modern switchmode supply using an adapter plate to allow use of the original screw mounts. The result is much cleaner internally, runs at a reasonable temperature with a light breeze on your fingers as you type, and you don't risk your house catching on fire.

This page was last updated on 3-11-2023

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