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.
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