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Old 26 November 2009, 11:09   #1
protek
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A3640 overclocking/upgrading

You who have overclocked your A3640, have you just changed the crystal and made modifications to the timing lines, if necessary or have you also changed the actual CPU? Do you still need to apply the timing fixes even if you change the CPU with the crystal?
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Old 26 November 2009, 11:33   #2
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@Protek

the A3640 is a fickle beast and depending on the pcb revision, components onboard, age and cpu your milage will vary... but lets say the following.

1. you have a Rev 3.1 (quite common) A3640 Masked Board

2. Its advised that you replace the capcitors as they have been soldered the wrong way round, the PCB silk is actually printed incorrectly

3. You use a 33mhz capable 040 or faster.

4. you provide active cooling (that heatsink AND fan)

5. desolder the exsiting crystal and install a 14 pin dill socket.

--

recently I modified an A3640 with the timing fix, that allows for a faster crystal, also I installed a 40mhz CPU on the card. alas although it worked at 25 mhz, I never got to test it further than that as I had no crystals.

I then sold this to my friend MagerValp on AmiBay, he then took it up a bit more with a switch for the delay line, also change the capacitors too.

In the end he managed 33mhz stable from the card, wich is 7mhz Overclock... in perspective terms thats just under 33% frequency overclock and about a 30% performance increase.

Without trying to sound condescending, I was both please and proud of MagerValp's efforts on the A3640 =D

Now the thing is, this its not a garantee, some may overclock to 40mhz, (thats an 80mhz crystal) however some few dont even break 29mhz ( 58mhz) so if you do this, please be aware that it MAY NOT provide much of an increase.

Its all about how quick the "glue" & CPLD logic is at sampling (latching) the signals from the motherboard.

Now bare with me, I will get you pics and diagrams for your use =D
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Old 26 November 2009, 11:42   #3
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Modifed A3640@25 MHz (Click for larger images)



In this pic you see the upgraded heatsink and Fan combination, under this is a FULL CORE (MMU & FPU) 040 rated for 40mhz



The unit has had the Timing Line modification (in Commodore Blue 30 Awg)



Also soldered Turned (gold plated) socket pins for changing of the Oscilator (crystal)





In great working condition



now getting the Cap replacement list and Delay Line mod instructions
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Old 26 November 2009, 11:49   #4
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@ Zetr0:
Thanks for the insight to the anatomy of the 3640. Mine's a rev 3.0 with cap change done.
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Old 26 November 2009, 11:49   #5
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You really need to find a MC68040RCxx which has the L88M or K63H mask sets as they run almost cold at 40MHz even without a heatsink & fan.
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Old 26 November 2009, 12:00   #6
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heres the Delay Line Fix

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Old 26 November 2009, 12:05   #7
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Zetr0 guru hardware
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Old 26 November 2009, 12:10   #8
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Quote:
Originally Posted by Anemos View Post
Zetr0 guru hardware
I concur.
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Old 26 November 2009, 12:23   #9
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Nice clarification, with much clearer pictures of a pre-existing mod

http://members.iinet.net.au/~davem2/...ock/a3640.html
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Old 26 November 2009, 13:59   #10
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Quote:
Originally Posted by Anemos View Post
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Quote:
Originally Posted by protek View Post
I concur.

truely... I am humbled.... its a good thing the wifes not here or she would see me blushing like a girl....

to be fair there are many way better than I, I just bring good looks to the party

Quote:
Originally Posted by alexh View Post
Nice clarification, with much clearer pictures of a pre-existing mod

http://members.iinet.net.au/~davem2/overclock/a3640.html
LOL., i was frantically searching for this in my links... I couldn't find it, hence I posted up the AmiBay Pics!!!

thanks for the Link Alexh the thread is all nice and round now =)
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Old 26 November 2009, 14:53   #11
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It should be noted that overclocking the A3640 also means overclocking the motherboard SIMMs. It's likely that the SIMMs will become unstable before the 040 does. The upshot is that you get a sorely needed boost in RAM performance.
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Old 26 November 2009, 16:01   #12
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@MagerVap

Its doesn't *overclock* perse' it just hammers the rams a bit harder (30% in the case of a 66mhz Osc on the A3640), the frequency is still the same as this is governed by the motherboard clock.

I will have to check but I do beleive its 28mhz.

However you are most correct in saying my friend that the memory is likely to give out (in the sense of keeping up and not in the sense of blowing up or damaging) before the A3640 lol!

@thread

A thought would be that you could change the RAM to 60 or 50ns, this might give you a little extra milage, although I do believe the real culprit of limit will be the latching logic that decodes / address the rams themselfs.

still worth it though =D
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Old 26 November 2009, 20:07   #13
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Quote:
Originally Posted by Zetr0 View Post
Its doesn't *overclock* perse' it just hammers the rams a bit harder (30% in the case of a 66mhz Osc on the A3640), the frequency is still the same as this is governed by the motherboard clock.
Sure, since regular DRAM isn't clocked, it simply has a certain access latency, but the effect is the same.

Quote:
A thought would be that you could change the RAM to 60 or 50ns, this might give you a little extra milage, although I do believe the real culprit of limit will be the latching logic that decodes / address the rams themselfs.
I tried unplugging everything but the chip ram SIMM, but still couldn't get it to boot at 40 MHz. Unfortunately I don't have any fast SIMMs lying around, and no oscillators for testing 35 and 37.5 MHz, but 33 MHz is likely not the limit.
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Old 16 July 2010, 08:58   #14
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thread necromancy

I now own the A3640 from Post 3 my question is How is the heat sink held on ?? is it gum, glue or wishful thinking hehehehehe

I want to replace the fan/heatsink as the one in the picture did`t last long, bloody thin wires and no surround for the fan..
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Old 16 July 2010, 20:58   #15
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You can glue the heatsink using a thermal pad, or even better: some artic silver paste in the middle of the CPU and then two little drops of superglue on two non-adjacent corners.
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Old 17 July 2010, 05:18   #16
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@cosmi

my friend the heat-sink is infact 4 smaller sinks with thermal glue based grip-pads - thanks to our friends at 3M =)

Basically the hotter the CPU gets the more the glue-pads bond and the better the heat effciency. You should be able to pry them off the CPU it might be a little difficult though.

The Fan that is on there sucks down so there is no need for a shroud, infact the shoud will probably buffet air and have a mild loss in performance - at the moment it creates a wide vortex - you could make your own with some small pastic strips or even plasticard =)
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Old 19 July 2010, 17:13   #17
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I have had fairly good luck with my a3640 overclocking attempts. My rev 3.0 runs stable at 36mhz, but will not even post at 40mhz. I am using a 40mhz 040 and 60ns ram that can run in "Ramsey skip mode" at 25mhz - 36mhz requires normal memory timings. The delay line made all the difference since without it, I was not so stable at 30mhz.
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Old 19 July 2010, 18:15   #18
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the biggest limmitation on the A3640 is the speed of the GAL's CPLD's on the board

Its bascially their latching and propagation time that goverens the end result - if one could find faster GAL's there exists the possibility of a safe 40mhz

I will say that its not just a case of finding a faster (in propagation and latching) 5v pin compatible CPLD - you will need to do some math in timings to make sure you dont out-latch the CPU or the Bus.
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Old 19 July 2010, 22:16   #19
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great I`ll attempt to pry away the heatsinks

the fan has long gone it had an argument with the ide lead and lost hehehhehe
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Old 12 August 2010, 11:49   #20
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>the biggest limmitation on the A3640 is the speed of the GAL's CPLD's on the board

All GAL22V10 are 5ns on my A3640 now
All GAL16V8 are 7ns now

But still 30.5 Mhz... No boot at 32 Mhz...


Some 74 need to be updated by faster ones ?
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