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Macintosh Performa 475 project

k24a1

Well-known member
Hello 68kMLA!
I have a Macintosh Performa 475 lying around that I recapped (a little poorly, got better since 2020) and it needs some love.
It's got a Motorola 68040 without a heatsink running at 25MHz, I think 10/12MB of RAM, 512K VRAM, a 1.44MB floppy drive, and no hard drive. My plan is to overclock its CPU to 33MHz (or 40 if I can deal with video issues?), find a good way to cool it, put a BlueSCSI in with a 4/8GB SD card, upgrade the VRAM to 1MB, potentially add L2 cache, and possibly even try tracking down one of those upgrade cards to use a PowerPC 601 if given the chance.
I have also heard you can get one of these to identify as a Quadra 605, but I am not sure what the benefits of that will be and I have heard there are performance issues.
I am not exactly keen on the power supply, so are there good replacements for these available?

Thank you for any help given!
-Nick
 

joshc

Well-known member
and possibly even try tracking down one of those upgrade cards to use a PowerPC 601 if given the chance.
Those cards go for around $500-600 and the slow 601 runs 68k code slower than an 040 does, just FYI ;-)

The resistor swap/mod you can do will get you from 25MHz to 33MHz which will be stable.


This also changes the gestalt of the Mac, so it no longer identifies as as 475.

Identifying as 605 does nothing other than it give the machine the gestalt ID of a 605.

Hope that helps, wish you the best of luck with it - the 475 is a great machine.
 

k24a1

Well-known member
Alright, so no PPC on that computer then. I have also heard there are ways to get L2 cache on one of these?
 

joshc

Well-known member
According to everymac, "This model had the option of a 256k cache on a riser card that plugged into the CPU socket. This cache card was socketed to hold the processor."

I've never seen one of these cards, probably just as hard to come by as the 601 card.
 

jajan547

Well-known member
Hello 68kMLA!
I have a Macintosh Performa 475 lying around that I recapped (a little poorly, got better since 2020) and it needs some love.
It's got a Motorola 68040 without a heatsink running at 25MHz, I think 10/12MB of RAM, 512K VRAM, a 1.44MB floppy drive, and no hard drive. My plan is to overclock its CPU to 33MHz (or 40 if I can deal with video issues?), find a good way to cool it, put a BlueSCSI in with a 4/8GB SD card, upgrade the VRAM to 1MB, potentially add L2 cache, and possibly even try tracking down one of those upgrade cards to use a PowerPC 601 if given the chance.
I have also heard you can get one of these to identify as a Quadra 605, but I am not sure what the benefits of that will be and I have heard there are performance issues.
I am not exactly keen on the power supply, so are there good replacements for these available?

Thank you for any help given!
-Nick
I've been looking for such a card to put in my LC475 (same macine)
 

Powerbase

Well-known member
The jump to 33MHz is a excellent idea. I've done it and the results are noticeable as almost everything speeds up, benchmark wise.

I've been wanting one of those L2 upgrades to for my 475. I believe the Sonnet Quaddoublers had a L2 cache on them, as well. I've only ever seen one for sale once though. I wish there were more as I believe the L2 cache did have a noticeable speedup.

I second skipping the PowerPC upgrades. You just end up with a really slow PowerPC.
 

jajan547

Well-known member
The jump to 33MHz is a excellent idea. I've done it and the results are noticeable as almost everything speeds up, benchmark wise.

I've been wanting one of those L2 upgrades to for my 475. I believe the Sonnet Quaddoublers had a L2 cache on them, as well. I've only ever seen one for sale once though. I wish there were more as I believe the L2 cache did have a noticeable speedup.

I second skipping the PowerPC upgrades. You just end up with a really slow PowerPC.
have you tried this? Also the chips needed are here supposedly you can get 50MHz.
 

MacKilRoy

Well-known member
if someone has a spare board I will buy it and do the 50MHz and post the results
There’s a product called the Spicy O Clock made by Kay Koba that has an adjustable oscillator. But to drive the display you need faster, 60ns VRAM. Otherwise you get garbled or black screen.

Kay Koba has overclocked his LC 475 to over 51mhz.
 

Powerbase

Well-known member
Id have to check to see the speed on my vram, probably bog standard 80ns though. Curses to you for mentioning someones running at 50MHz. My 33Mhz 475 seems so middling now.
 
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