We designed an FPU card for the Mac Classic II that offers a balanced performance. The card is designed to save space and avoid unnecessary bulk, while allowing users to choose useful components. This card has the capability to overclock the FPU. It has been observed that as the FPU is gradually overclocked, the CPU performance decreases in inverse proportion. Therefore, it is best to find an optimal balance. It has been confirmed that the FPU can be overclocked up to 40MHz, but based on personal experience, keeping it around 25MHz maintains better CPU performance.
 
FPU Overclocking Method
 
1. Desolder the solder pad of J3, which is pre-soldered for selling. Using a soldering iron of about 80W or higher should effectively separate the two pads. This will enable the J2 overclocking selector jumper pin. *3rd pic
   
2. Install a 1x3 jumper pin on J2. By moving the jumper pin, you can choose between using the CPU clock or the crystal oscillator on the card. As indicated on the back silkscreen, SYS is for the system clock (the same as the CPU clock), and OSC is for the crystal oscillator on the card. If you only use the crystal oscillator on the card, you may secure it with a suitable wire and solder it in place. *3rd pic
 
3. Install a crystal oscillator at location X1. The recommended frequency range is around to 33MHz. Use a 5V driven oscillator. Both 8-pin and 14-pin sizes can be used. Be sure to align the orientation correctly by not losing sight of the dot at pin 1. There is no physical interference with this, so if you don't mind a little height you can use a pin socket. *4th pic
 
Option:
Refurbished Motorola MC68882s are available for use with this card. They are randomly selected to be 33MHz or higher. The verified units are shipped attached to the card.