It's definitely a joy to bring this installment of PS/2 Unplugged online. I had heard of Jim Shorney's mods for the 8573 P70/P75 portable machines, but until you see his mastery of solder it's hard to appreciate the advanced level of of this upgrade. This is likely to be one of the most challenging PS/2 modification you'll run across, but is well worth the effort as it opens up many processor upgrade opportunities for the P75 portable that would otherwise be non-existent.
IBM designed the 8573 P75 series "portables" to use processor cards, similar in concept to some of the other PS/2s that use processor complexes. However, there was never an upgrade card to improve on the performance of P75 machines. What's worse, the stock 486DX-33 processor card was implemented without a processor socket. What this means is that the CPU was shipped soldered directly to the processor card itself.
Here's a close-up look at the stock 486DX-33 CPU mounted on the processor card:
Take special note of how the pins from the processor go straight into the PCB board itself and is soldered in place. The following picture of the back side of the processor card reveal the grid of soldered CPU pins.
Well, a soldered-in CPU obviously does not allow for much in improving the processing power, so Jim took the situation into his own hands with the help of a Pace vacuum-powered desoldering station. With steady nerves and a lot of patience, Jim actually removes the soldered-in processor! With the processor off the complex, there is a grid of 168 holes where the processor once sat. So, the final process in modifying the processor card requires that a PGA socket be soldered in to replace the CPU, to which Jim says "your hand gets awful damn tired" when you're done. The end result can almost be thought of as a masterpiece.
Here's how the processor card looks once Jim has replaced the CPU with a socket:
And here's the backside... Jim's meticulous soldering makes the complex look as factory as *before* the socket mod:
Just to get a really good idea of how clean of a job Jim does on the desoldering, look at the resultant holes left by where the processor pins used to be.
The conversion of the processor card to use a socket for the CPU allows for some nifty upgrades. Jim has used both the Intel DX4-100 Overdrive as well as the AMD 133 MHz processor on his previous upgrades. Here's a picture of the completed mod mounted with CPU back into the P75 portable:
Of course, with a PGA socket in place, there's always the possibility of installing the popular Kingston Turbochip as well:
My personal opinion on this mod is "Wow..." (jaws dropped) and kudos to Jim for exploring this territory. If you've ever wondered whether upgrading the P75's processor card could be done, Jim has definitively laid that question to rest.