slomacuser
Well-known member
I replaced the processor of Quadra 700 (68040/25) with the more powerfull processor from Quadra 840 (68040/40) and the clock speed remains same 25 mhz?? What should I do to anable the full speed of 40 MHz?
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Quadra CPU upgrade
- Thread starter slomacuser
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ChristTrekker
Well-known member
The rating on the chip only signifies the speed the chip is rated for achieving safely. There is a small crystal on the motherboard that vibrates at a frequency that serves to drive the processor at the given frequency. To make use of the extra speed the replacement CPU is capable of, you need to replace that oscillator with a faster one.
equill
Well-known member
Dropping in a faster processor speeds up a Mac only if the Mac has been designed so that the processor (or the daughter-card that carries the processor) controls the system bus speed, directly or as a multiple of bus speed. That isn't so in the Q700. Your faster processor is confronting the original 25MHz oscillator, and loses the battle. Even if you replace the oscillator successfully, there is no guarantee that auxiliary chips on the logic board can cope with a higher system bus speed. If you search the literature you will find out what others have achieved in trying to 'overclock' the Q700.
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Franklinstein
Well-known member
Sonnet made an upgrade for '040s that used a carrier device that harbored a 40MHz '040 and plugged into the original processor socket. The carrier doubled the clock input of the system bus, thus the processor ran at the full frequency.
Since it's only a 40MHz chip, I've only seen one machine that had a 20MHz processor to replace, and that was the Quadra/Centris 610. I've tried using the upgrade in a 25MHz bus machine (which overclocked the processor to 50MHz), but it usually overheated, so all I could ever use it in was the 610. If you can find one of these upgrades on eBay, you can always try it yourself.
As far as other methods, only replacing the clock crystal like equill said would get you a faster processor. However, it would probably be flaky at best as other chips on the board may not be able to handle the higher frequencies.
Since it's only a 40MHz chip, I've only seen one machine that had a 20MHz processor to replace, and that was the Quadra/Centris 610. I've tried using the upgrade in a 25MHz bus machine (which overclocked the processor to 50MHz), but it usually overheated, so all I could ever use it in was the 610. If you can find one of these upgrades on eBay, you can always try it yourself.
As far as other methods, only replacing the clock crystal like equill said would get you a faster processor. However, it would probably be flaky at best as other chips on the board may not be able to handle the higher frequencies.
slomacuser
Well-known member
thx for answers .... anybody intersted for Q700? or 68040/40 processor
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