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 upgrade part I was interested in was a Texas Instruments TX486SXLC2-050-PJF. That processor runs a 50 MHz internal core from a 25 MHz external bus and comes 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.

Unfortunately, similar clocks and packaging do not automatically make a CPU a drop-in replacement. The 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!

Sources