Quadra 605 40 MHz upgrade

[Aoresteen]

My Quadra 605 is running at the factory speed of 25 MHz. I did put in a 33MHz 68040 but have never bumped up the speed.  I recently bought a 68040 40MHz cpu and I'm getting ready to bump up the speed.

IIRC the 605 doesn't handle 40MHz very well.  What's the fastest I can run it in a Q605 and have the system remain stable?

Thanks!

 

[BadGoldEagle]

Have you seen this?

https://drive.google.com/file/d/0B9rTgRm4OkZwT2FDRjhqS2YzMFk/view

Apparently it's stable as long as you don't use a Pivot PDS card...

33Mhz is easily achievable by moving around a couple capacitors. IIRC the Canadian version of the LC475 ran at 33Mhz natively.

Edit: I'd recommend installing a heat sink on that 40MHz 040. These things can get hot quite fast.

 

[MJ313]

33Mhz is easily achievable by moving around a couple resistors. 

FTFY

 

[BadGoldEagle]

33Mhz mod: Move R25 to R22 and R21 to R24

My bad, it's resistors not capacitors. In my defence they look the same  [] ]'>

 

[trag]

If one does the 40MHz upgrade, one may also need to upgrade the VRAM.  IIRC, some 80ns VRAM isn't fast enough to work properly once the Q605/P/LC475/6 is running at 40 MHz.   Or is it 100ns that's too slow and 80ns is good?  Can't remember.  Arr.   Whatever the two common VRAM speeds are the slower one may not work at 40 MHz.

 

[Trash80toHP_Mini]

Be mindful in your choice of heat sink form factor or be ready to trim it back at an angle to clear the tall, high capacity SIMM you'll likely want to use.

Are DRAM speeds also be an issue? I'm going by Q840AV specs for a possible procswap.

 

[BadGoldEagle]

IIRC, some 80ns VRAM isn't fast enough to work properly once the Q605/P/LC475/6 is running at 40 MHz.   Or is it 100ns that's too slow and 80ns is good?

According to everymac.com, the Q605 shipped with 80ns VRAM SIMMs (I am no LC expert so I can't verify that). Might be worth checking out even faster SIMMs though! I've always wondered how the system would react to 1.5 or 2Mb of VRAM... Maybe it could do 24 bit colour?

 

[Trash80toHP_Mini]

Check the DevNotes for the video controller (most likely integrated into an ASIC?) against other models. If you can find one that supports 24bit uisnt it then maybe. if you can't find a parallel 24bit implementation outside the 605/475 family it's likely a RAMDAC limited situation of a low end/mid-range ASIC. Might be able to bump 21" res to 16bit with a VRAM infusion though.

Either would be limited by the number of CAS and RAS lines available on VRAM slots or unimplemented lines present on the controller IC's legs for jumper cabling.

UGLY hack no matter which way it might be done.

 

[Aoresteen]

Thanks all!  I *think* my VRAM is 70 NS so it should work.  I have a 128MB RAM stick in it but I do not remember the speed.  I will take it to 33 MHZ first,.

I'm considering using a water cooling system.

BadGoldEagle, thanks for the link.  I've seen it in the past and will study it further. I was wondering if I could ove-clock  it to 50 MHz?  Heat will be an issue.

BadGoldEagle

 

[trag]

Are DRAM speeds also be an issue? I'm going by Q840AV specs for a possible procswap.

All the 64MB and 128MB SIMMs I've seen are 60ns or faster, so DRAM speed should not be an issue, unless one goes retro with a really old, slow, small SIMM.

 

[Aoresteen]

Thanks all.  I've been working non-stop since Saturday as a HAM radio guy with ARES due to Irma.  Spent all day yesterday in our local Georgia County EOC passing traffic to NWS.  We were very fortunate as Irma passed us by to the west and we had minimal damage and no fatalities.  I'll  have to put this project on hold for a bit (again ) as I catch up on the storm & other pressing projects.

 

[trag]

I am glad to read that you came through the hurricane okay.

 

[rsolberg]

Glad to hear you made it out the other side of Irma. Hats off to you for your public service. In this age of pervasive infrastructure-based communication, the public doesn't always realise the importance of point-to-point communication and HAM operators until an event or disaster disrupts or destroys said communications infrastructure.

As for RAM timing, don't forget the 4MiB of system RAM soldered to the logic board. 80ns should be okay at 33MHz, but at 40MHz, my rudimentary math with clock latency leads me to believe that the RAM needs to be 75ns or faster. I've successfully overclocked to 41MHz using 60ns RAM, but I haven't tried 70ns. If the soldered RAM is 80ns, this might preclude running the board at 40MHz reliably. The same probably applies to VRAM modules. I've had very poor luck with 80ns VRAM above 33MHz, but I've had luck with 70ns to 41MHz. Unfortunately, I've found the 70ns or faster VRAM is pretty scarce.