20MHz Daystar Turbo 040i Speedup
The Daystar Turbo 040i 20MHz card in a Mac IIsi can be clock chipped to roughly 40MHz with virtually no loss in stability. A few pointers from Brad Wilson (bwilson@deltanet.com) are included below with regards to the modification.
Background
- The original crystal oscillator on the card is a 10MHz full size metal can which gives a 20MHz card.
- This is the board without the FPU, but it probably makes no difference.
- Initially the Mac IIsi itself was not clock chipped.
- Later the Mac IIsi was clock chipped, and there was a speedup in the video.
Modification
- Replacing the oscillator with a 4 pin IC socket enabled an easy testing platform where different oscillators could be tested. Be careful when removing the original crystal oscillator as the card is a multi-layer PCB and Daystar did a great job in soldering the crystal onto the board. An industrial-grade desoldering station with vacuum pump can be very handy.
- Install a heatsink on the 68LC040.
- If you have extra heatsinks you may want to install them on some of the other smaller components on the board; they get pretty warm.
Results/Performance
- With a 12MHz oscillator (24MHz) the machine was rock solid.
- With a 14MHz oscillator (28MHz) the machine was rock solid.
- With a 20MHz oscillator (40MHz) the machine was rock solid.
- This is as fast as he tried.
The latest version of the Turbo 040 software is QuadControl Cdev v2.3
If you have any questions feel free to contact Brad Wilson (bwilson@deltanet.com)