An on-board FPU for LC II
visitors since Dec. 28, 1998
Japanese version of this page.
Background
Macintosh LC II appeared as the successor of the first Lowcost Color Macintosh LC. It had a 16MHz 68030 CPU in contrast to LC's 16MHz 68020 which didn't have MMU inside. It had 4MB of memory on the logic board and two SIMM slots for 30 pin SIMM. Although they accept 4MB SIMM's, the total memory size is limited to 10MB. As for the video output, it had a SIMM slot for VRAM of maximum 512kB. It also had an expansion slot called LCPDS. There are no FPU sockets on the logic board. Generally speaking, it seems completely out of date for contemporary application softwares.
However, another usage for old 68030/040 Macintoshes is a Unix server with NetBSD. It requires a 68882 FPU to run NetBSD steadily. To install 68882 FPU on the LC II, you must install 68882 expansion card on the expansion slot. In this case you can run NetBSD. However you cannot connect to Ethernet, since Ethernet card needs another expansion slot. So you cannot get FPU and Ethernet at the same time. When I closely looked at the logic board, I found a series of holes for an LSI at the side of the CPU. They looked like the holes for FPU socket. I guess LC II was designed to have an FPU on the logic board as an option, but even a socket was eliminated to cut off the price.
Caution: If you perform this modification, you will lose the warranty from Apple. Do it yourself with your own risk.
Method
tools required
- soldering iron for IC's. (1mm chip)
- solder absorber
I used an FPU and an FPU socket removed from an FPU expansion card made by Interware Co. Ltd.
Modification procedures
- Removal of an FPU socket
At first, 68882 was removed from the socket.
After warming a pin of socket with a soldering iron, solder was aborbed with an absorber. It was really complicated work to do. ;-(
- Logic board preparation
There are a series of holes for an FPU socket on the logic board. However, the holes are filled with solder. So you cannot install socket without removing the solder from the holes.
Top view of LC II logic board. A red square indicates the location of FPU.
First, a logic board was placed perpendicularly. You point a hole with a soldering iron from the top side of the logic board and absorb the solder from the bottom side. The same procedure should be repeated at least twice.
At last, the holes are grinded gently with a small awl.
- Socket installation
The FPU socket should be inserted with the guide of white dotted line on the logic board.
You must solder with maximum caution.
- Start up and testing
At first, you start up the LC II without installing the FPU to make sure that you performed nothing wrong on the logic board.
After you shut down the LC II, install the FPU and turn on the switch.
Results
Confirm whether the FPU is running correctly with a diagnostic tools such as TechTool.
Now you can get the FPU and Ethernet expansion card at the same time.