33MHz Daystar Turbo 040i Speedup

Background

• This is the board without the FPU, but it also works with the regular 68040.
• The original crystal oscillator on the card is a 16.5MHz full size metal can which gives a 33MHz card.
• Unfortunately, attempts to disable the onboard oscillator by grounding pin one and feeding in a new signal failed.

Modification

• Replacing the oscillator with a 14 pin IC socket (with the inner 10 pins removed) 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.
• A CPU fan was fitted on top of the original heatsink.

Results/Performance

• With a 20MHz oscillator (40MHz) the machine was rock solid.
• With a 21.835MHz oscillator (43.67MHz) the machine was similarly stable, and crashed only twice within a one month period. It is not clear if the crashes were caused by the clock upgrade or new software extensions. This speed seems just right.
• With a 24MHz oscillator (48MHz) the machine crashes on startup. After 30 minutes of warming it stabilizes, but this is not stable enough for day-to-day use.
• At 43.67MHz, the machine rates faster than a Quadra 840av. A side benefit of this speedup is that the built-in video now runs faster than the Apple 8¥24 NuBus video card. Plenty of disk cache also helps.
• Using a digital thermometer, the internal temperature varied between 33 and 35°C after an hour of use.
• Quadcontrol actually recognizes the card as a 40MHz Turbo 040.
• More recently, others have accelerated these boards up to 48MHz with a 24MHz oscillator.

If you have any questions feel free to contact Tan Tywee (tantywee@singnet.com.sg)