80Mhz crystal and 040@40mhz in an A3640...

[Jose]

Hi. Hi have an 80mhz crystal lying around and also an 040 wich runs at 40mhz native speed. I also have an A3640 board wich is running an 040 at 25mhz.

My question is simple, do you think I risk ruinning the board if I try an 80mhz crystal, is it prepared for it?
I won't have any problems trying the 040@40mhz as the current 040@25mhz in the board is socketed:-)
By the way, do you think the value of such a modified board is worth the risk?

[Tumo007]

I don't think it will works for a long time... the 50mhz cristal on the A3640 also provide the system clock for the A3/4K mobo... At one point I managed 33mhz on such setup but I had to add a heatsink/fan on the Ramsey chip... it was pretty fast if you keep in mind that the 040 had to access the fastram on the MoBo @ about 12meg/sec. But since I have a CV64/3D the write to the card were also speeded up whitch is "a good thing"tm

If you are brave enough to try it out you'll have to make a small modification to the A3640; Look for "Dave's Amiga overclocking page"

CU

[adz]

Tumo007 wrote:
I don't think it will works for a long time... the 50mhz cristal on the A3640 also provide the system clock for the A3/4K mobo... At one point I managed 33mhz on such setup but I had to add a heatsink/fan on the Ramsey chip... it was pretty fast if you keep in mind that the 040 had to access the fastram on the MoBo @ about 12meg/sec. But since I have a CV64/3D the write to the card were also speeded up whitch is "a good thing"tm

If you are brave enough to try it out you'll have to make a small modification to the A3640; Look for "Dave's Amiga overclocking page"

CU

CU as in CU_AMiGA???

[Jeff]

This has been tried.  I remember years ago it was decided that the logic onboard the A3640 is not reliable at any speed much beyond 33mhz even if a faster CPU is used. I doubt you will hurt anything by trying, but it almost certainly won't work for any period of time.

Jeff

[Jose]

"If you are brave enough to try it out you'll have to make a small modification to the A3640; Look for "Dave's Amiga overclocking page".

I wouldn't mind risking the card a bit, but since it also provides the system clock to the A3/4K motherboard I don't know if I want to risk the A4000 itself. At the moment I'm waiting for a CyberstormPPC233 060@66 to arrive at any minute you know  :-D

[Crusher]

Jose, is it an OC 50MHz? What cooler is it then?

[Jose]

@Crusher
Currently it's not an OC, I got no cooler in it. Running the A4000's mobo through an 80mhz crystal with this card wouldn't probably be a good idea though..

[Effy]

I have read that overclocking the 3640/25 to 30 Mhz doesn´t give any problems at all, but a fan might be nice to play it safe  :lol:
I´ve got a 3640/25 myself and I´m gonna have it overclocked too to 30 Mhz, much cheaper than buying a 40 Mhz turboboard  :-)

[SpeedGeek]

A3640 @40Mhz. Been there. Done that!
http://eab.abime.net/showthread.php?t=49057

[AndyLandy]

The A4000 motherboard isn't clocked off the CPU card. If you have an A3630 card, that's clocked off the motherboard, so you can't overclock it without overclocking the whole system. This isn't true of the A3640, that's independently clocked. The problem with overclocking the A3640 is that you are also overclocking the glue logic on the card. You'd have to be very lucky to get a card that will tolerate a 40MHz clock.

[mechy]

I managed 34mhz on a A3640 rev 3.2 with the delay line hack and a 33mhz 040 chip.
at the time i hadnt pushed it any farther(no faster osc's within reason),but it was rock stable and quite a diff. over the stock 25mhz.I used 60ns ram on the motherboard although this may not of mattered but its a safe bet.sold the 4000 to a toaster user years ago who really liked it.
I used a good fan and also heatsinked the hotter running pal's on the board just in case.

[SpeedGeek]

The A4000 motherboard isn't clocked off the CPU card. If you have an A3630 card, that's clocked off the motherboard, so you can't overclock it without overclocking the whole system. This isn't true of the A3640, that's independently clocked. The problem with overclocking the A3640 is that you are also overclocking the glue logic on the card. You'd have to be very lucky to get a card that will tolerate a 40MHz clock.

The slowest device on the A3640 (except for the 040 Cpu) is a 15 ns Pal or Gal chip (most A3640's have 10 ns or faster) and these are rated by their manufacturers to run at 50 Mhz or above. However, the Amiga custom chips on an A3000 or A4000 motherboard were designed to run at a mere 28 Mhz! So you're lucky if you can overclock your motherboard at 33-35 Mhz. Also, Ramsey is highly dependant on the speed of the installed Fast memory. Also, The A4000 must receive it's Cpu clock and Clock 90 from the Cpu card in order to support the A3640.

[AndyLandy]

The slowest device on the A3640 (except for the 040 Cpu) is a 15 ns Pal or Gal chip (most A3640's have 10 ns or faster) and these are rated by their manufacturers to run at 50 Mhz or above. However, the Amiga custom chips on an A3000 or A4000 motherboard were designed to run at a mere 28 Mhz! So you're lucky if you can overclock your motherboard at 33-35 Mhz. Also, Ramsey is highly dependant on the speed of the installed Fast memory. Also, The A4000 must receive it's Cpu clock and Clock 90 from the Cpu card in order to support the A3640.

I thought the whole point of the A3640 is that you don't overclock the chipset, the card is independently clocked from the motherboard. I understand that's why you can't overclock the A3630, since it's synchronously clocked with the motherboard, but the A3640 isn't. So what am I missing here?

[SpeedGeek]

I thought the whole point of the A3640 is that you don't overclock the chipset, the card is independently clocked from the motherboard. I understand that's why you can't overclock the A3630, since it's synchronously clocked with the motherboard, but the A3640 isn't. So what am I missing here?

What you are missing is an understanding that the A3640 is a synchronous accelerator which was designed to run at the same clock speed as the motherboard. The clocking difference between the A3640 and A3630 is the motherboard receives the clock from the A3640 and the A3630 receives the clock from the motherboard. If the A3640 had been an asynchronous design then the 40Mhz barrier would have been broken a long time ago.

[AndyLandy]

What you are missing is an understanding that the A3640 is a synchronous accelerator which was designed to run at the same clock speed as the motherboard. The clocking difference between the A3640 and A3630 is the motherboard receives the clock from the A3640 and the A3630 receives the clock from the motherboard. If the A3640 had been an asynchronous design then the 40Mhz barrier would have been broken a long time ago.

aah *realisation dawns*

That makes sense now. Quite why the big C= felt the need to do this differently between the '030 and '040 card is beyond me, but so are many of their decisions. Thanks for the info. :-)