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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Brian on March 06, 2005, 10:37:14 PM
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One of my A4000 have a 040 card and although it's quite fast I'd rather have more compability, especialy with older demos, games and such.
So I've been toying with the idea of trowing in an 3630 card in it instead just for kicks. BUT 030/25 is so not gonna cut it so I was thinking if it was possible to overclock these cards some? I see a place for a crystal but dont know if it's for FPU, CPU or both. If for CPU or both can I just drop in a faster crystal and set the motherboard jumper to external clock or do I need to do more? If not for CPU is there a way to hack in a fast crystal easily by cutting a few lines and whire it in?
I'm thinking OC to 33Mhz or perhaps 40Mhz should be ok with some extra cooling, wish there was a socket for the CPU so one could replace it easily but no there's not. Doesnt look to be much else on the board that could bog out cause of too fast a clock so I'm thinking OC can go as far as the CPU can go, am I correct in this assumtion?
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I would say you can do 33MHz easily. Any higher would be bad. Not sure if it will work but give it a try. I would install a socket for the oscillator. It you get into WB and it runs stable you are good to go. If it doesn't then revert back to 25MHz.
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Since some cards contained a 50Mhz 030, this might not be out
of the question. It depends on the quality of the processor
I suppose.
C Snyder
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The A3630 get`s it`s clock from the mobo, the crystalsocket on it is for the FPU. You could overclock the whole machine by replaceing the 25MHz crystal on the A4000 board by an 33 MHz one. Could lead to problems with older zorrocards, but in general it works.
For some real speedinprovements while holding compatibility better go for a Blizzard 4030, it runs at 50MHz by default.
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Overclocking the A3630 :
The A3630 is the standard 68030 CPU card supplied for A4000 Amigas. It takes it's clock from the A4000 motherboard, although a space is provided for a socket enabling the 68882 FPU (if fitted) to be clocked separately if desired. Overclocking involves removing the 50MHz oscillator on the motherboard and replacing it with one of a higher frequency. The motherboard divides the signal by 2, so to get 33MHz, you will need to fit a 66MHz oscillator. 33Mhz is the highest speed I could get reliably by simply changing the oscillator. This limitation is partly caused by the use of a delay line on the motherboard to generate a second system clock, delayed by 90 degrees. This delay is fixed, so that if the frequency is changed, there is no longer the correct amount of delay to provide a 90 deg clock.
The delay line chip provides several tappings to provide different amounts of delay. Selecting a tapping that provides a shorter delay will help provide the correct 90 deg delay when a higher clock signal is used, increasing reliability and allowing even more overclocking. With the delay line tap changed, I was able to get to 35MHz, using a 70MHz oscillator. Unreliable operation was available to 37.5MHz, using a 75Mhz oscillator. Note that as we are changing some motherboard timing so you may get better - or worse results than me. These variations could be caused by different Zorro III cards and different SIMMs etc. In other words, your mileage may vary. I recommend changing the delay line tap if you intend to overclock at 33MHz or over. Below 33Mhz, the standard delay tapping is still the most appropriate.
The 030 chip used on the A3630 is of a later version, and it still runs quite cool, even at 35Mhz, so a heatsink should not be required.
Thanks to "Dave's Amiga Hardware Page" :-)
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Ok... so the crystal place is for the FPU that's noneprecent on my board. Not so good then. What about hacking the board to support an external clock for the CPU, thinking cutting traces and whire a crystal to that somehow, is it possible?
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Why not just replace the crystal on the motherboard by a 66 Mhz one ???
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Why not just replace the crystal on the motherboard by a 66 Mhz one ???
Because it doesn't work !!!
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I'm not gonna risk a motherboard for this, the 3630 card is a spare so that one I can risk blowing.
But is there no info out there on how to whire up a faster crystal to the CPU on the 3630?