Fujitsu FM Towns CPU Upgrade Log

[JAMMArob]

Hey guys!

I thought I would share my experience upgrading the CPU in my FM Towns model CX-20.



For those of you not familiar with the Fujitsu FM Towns, these were a line of PCs sold in Japan during the early 90s. While the early units use a 386-16 (DX or SX depending on the model), they are not Windows compatible PCs. I see it as more of a game system. Here is a brief video I put together about the machine:
http://www.youtube.com/watch?v=Th4c7fTMETI

Most games run pretty well on it's mediocre 16 MHz 386, but there are some that run like a drunken turtle. While Fujitsu released newer models that featured 486 processors, they lacked the styling of the original models. This lead me to attempt a CPU upgrade!

Unlike most IBM compatible PCs running similar CPUs, the CPU in the FM Towns is a PGA 132 ceramic package that is soldered directly to the board. No easy upgrades here.


Fortunately, there is a gentleman local to me that is a master at soldering. He was able to desolder this CPU, and solder in a 132 pin machine socket. He also installed a socket that allows me to swap the crystals that control the CPU speed! The first CPU I tested was the AMD Am386DX-40. The fastest 386 you can find.

The results? No boot at 40 MHz. No boot at 33 MHz, and the games would not load at 25 MHz. Unfortunately due to the 386's 1:1 CPU to bus ratio, cranking up the CPU speed also affects the speed of the memory which is not cut out to run above 20 MHz. So that is where it has stayed.

I swapped out the 386DX-40 for a TX486DLC and gained a marginal speed boost, but I need more power!

My next test will be the Cx486DRx2, if I can find one. Hopefully the Towns won't mind a little clock doubling!

[ComputerHoarder]

neat looking towers i like

[mwdmeyer]

Wow very cool. Cd rom but no hdd is odd!

[Neology]

Nice Game Machine

[gshv]

I noticed that the processor on the picture has TWN abbreviation after S-Spec number, which is unusual for 80386 processors. Another Intel processor with TWN abbreviation was SX098, which is also 16 MHz chip. My wild guess is TWN chips were produced for Fujitsu FM Towns computers, unless TWN stands for something else, like Taiwan I found this thread with more pictures, some of them were probably posted by JAMMArob:

http://nfggames.com/forum2/index.php?topic=2130

One of the pictures shows AMD 80386 processor with DS39473A part number. DSxxx is an AMD custom part number, so it seems they were also made just for Fujitsu.

Gennadiy

[i440bx]

TWN stands for Fujitsu FM ToWN.

[JAMMArob]

Yep, that was me!

I still have the original CPU. The CPU is safe and was professionally desoldered.