The time has come. We wish you a safe journey, AMD 386SX CPU. You have served us well. Armed with a heat gun and flux, work begins on my attempt to create a 50 MHz Amstrad Mega PC.

That 50 MHz target needs a little explanation. The original Am386SX does not run its core at the full CLK2 input frequency. A 50 MHz CLK2 signal corresponds to a 25 MHz 386SX core. The replacement chip shown in the later repair photographs is marked TI486SXLC2-G50-PQ. It belongs to TI’s clock-doubled SXLC2-G family, designed for a 50 MHz internal core from a 25 MHz external bus in a 100-pin QFP package. So the idea was not to force the entire Mega PC motherboard to run at a 50 MHz external bus speed.

Looking back, similar clocks and packaging do not automatically make a CPU a drop-in replacement. The SXLC2-G needs a 3.3 V core supply, despite having 5 V-tolerant I/O. The supply voltages, motherboard chipset, BIOS, cache-control signals, pin compatibility and surrounding circuitry all have to cooperate as well.

This was very much an experiment.

I was also using a general-purpose heat gun for the removal. Having now spent more time doing this sort of work, controlled hot-air rework equipment with proper temperature and airflow control is a much better tool for removing a soldered QFP CPU from a vintage multilayer board.

Edit: Everything is on fire! What have I done! Flames everywhere!

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