Quadra (700, 900, 950) & Upgrades

[johnklos]

trag: ArmorAlley's Quadra 605 isn't overclocked - the motherboard runs at the stock 25 MHz and only the CPU runs at 50 MHz by way of the Quadra Overdrive, so there wouldn't be any issues with VRAM.

I've overclocked many Quadra 605s to 40 MHz, but because I typically don't have monitors, 832x624 at black and white is fine. Some of the issues I've seen are resolutions not working at all, the picture getting cut off 40 or 50 pixels from the right side, higher color depths causing loss of sync and so on. It can be quite interesting!

 

[trag]

trag: ArmorAlley's Quadra 605 isn't overclocked - the motherboard runs at the stock 25 MHz and only the CPU runs at 50 MHz by way of the Quadra Overdrive, so there wouldn't be any issues with VRAM.

I've overclocked many Quadra 605s to 40 MHz, but because I typically don't have monitors, 832x624 at black and white is fine. Some of the issues I've seen are resolutions not working at all, the picture getting cut off 40 or 50 pixels from the right side, higher color depths causing loss of sync and so on. It can be quite interesting!

Thank you for the clarification John.   Any idea what speed VRAM is needed to guarantee proper operation at 40 MHz?  I think I read that 80ns would do the trick, but my memory is hazy.

 

[ArmorAlley]

Hi Trag + Johnklos,

It's funny that you mention the VRAM. The one bother I do have with my upgraded system is with video. I can only get 640x480 now. I have two 512K Apple VRAM SIMMS in there. It doesn't bother me much, because its function is for games (like Marathon) and to act as server. I had to replace the 1600x1200 monitor it was driving with a 1024x768 one. I had suspected the cables and VGA adapter until this.

 

[johnklos]

trag: There are a few ways to get to 40 MHz. The simplest, which is to add a 20 MHz crystal oscillator, seems to work best regardless of VRAM, plus I've seen instances where even faster VRAM doesn't make a difference. Sometimes it's just something on the motherboard which doesn't want to run faster.

For reference, this is how I've done most of them:

http://mail-index.netbsd.org/port-mac68k/2002/05/31/0006.html

And here's the site that had the original information (from archive.org):

https://web.archive.org/web/20040715065245/http://gabezing.sytes.net/LC475-40Mhz-E.html

I've also tried the non-oscillator speedup, but have had more variations in measured speed and more video issues. Here it is for reference:

http://www.applefool.com/clockchipping/q605_40.html

ArmorAlley: Yes, it's most likely your VGA adapter. Try a different one. I can get 1152x870 at 256 colors with generic adapters and 512K VRAM SIMMs.

 

[trag]

trag: There are a few ways to get to 40 MHz. The simplest, which is to add a 20 MHz crystal oscillator, seems to work best regardless of VRAM, plus I've seen instances where even faster VRAM doesn't make a difference. Sometimes it's just something on the motherboard which doesn't want to run faster.

For reference, this is how I've done most of them:

http://mail-index.netbsd.org/port-mac68k/2002/05/31/0006.html

Thank you, John.  I'll have to remember this thread for when I have time to look at the Q605s again.   There were two or three 40MHz speed ups posted on Marc Schrier's site at one time or another.  I don't remember which one I used any more, except  that I did  install the faster clock buffer chip, (MC88916?).  

I've done the 33MHz before without issues.  I have some 20MHz oscillators kicking around somewhere.  I'll have to give that method a try.