New LC475 user - Questions on PowerPC upgrades

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maikol

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Sep 15, 2025
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Hello everyone, I recently got into retro Mac machines after coming from the retro PC side of things. As a beginner, I picked up a basic LC 475 and have done two upgrades so far. I recapped the power supply (it wasn’t even powering on) and upgraded the VRAM. My next step is to recap the motherboard, since I’ve read that’s often the next thing to fail.

I’ve also read about upgrading to a PowerPC processor via a DayStar card (saw a post here from kai.robinson)

For those who have done this upgrade, how does it feel in day-to-day use? Is the machine noticeably snappier or more responsive? I know it’s subjective, but I’d love a general sense of what people typically experience and whether it’s worth it. For me, it’s partly about “completeness”, following through on the upgrades that were available for this machine.

Cheers
 
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ClassicHasClass

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Aug 30, 2022
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I've generally found PowerPC upgrades for 68K Macs of questionable value these days. Back in the day they made sense to run software you couldn't run on your otherwise expensive hardware, but nowadays they simply make them into a poor low-end system. I have an Apple 601 card for my Q800 and I barely use it - there are many better Power Macs here to run stuff on.

Are they faster? Yes, and measurably so, but they are necessarily held back by the bus and other considerations, so they will never exceed or arguably even approach a real Power Mac. They're also not at all cheap and some have compatibility issues.

That said, collector's value always counts in this hobby, and they certainly do have that.
 
Trash80toG4

Trash80toG4

Active Tinkerer
Apr 1, 2022
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Concur, the somewhat less sexy of the Q605/LC475 twins would be one of the primo examples of the 68040 generation. If you've a need to run PPC code you're better off with even the lowest rung of the lineage leading up to the P6360/6300.

A full '040 would make a much better upgrade IMO.
 
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phipli

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Sep 23, 2021
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maikol said:
Hello everyone, I recently got into retro Mac machines after coming from the retro PC side of things. As a beginner, I picked up a basic LC 475 and have done two upgrades so far. I recapped the power supply (it wasn’t even powering on) and upgraded the VRAM. My next step is to recap the motherboard, since I’ve read that’s often the next thing to fail.

I’ve also read about upgrading to a PowerPC processor via a DayStar card (saw a post here from kai.robinson)

For those who have done this upgrade, how does it feel in day-to-day use? Is the machine noticeably snappier or more responsive? I know it’s subjective, but I’d love a general sense of what people typically experience and whether it’s worth it. For me, it’s partly about “completeness”, following through on the upgrades that were available for this machine.

Cheers
Click to expand...
You might want to try this : https://macintoshgarden.org/apps/control-strip-475-overclock

To get it reliable at 40MHz, you'll want to swap the 0 ohm resistor from R96 to R95. For 40MHz you shouldn't need to do anything else, but if you want to go faster you'll need to swap the chip (swap in the chip shown as MC88916DW80 in my photo) from the 88920 or 88916DW50 or whatever is already fitted.

1766492395995.png


The PPC upgrades are unaffordable. I should have bought one years ago but didn't. Absolutely not worth it now. Just buy a newer mac. (I'm not going to pay $500+ for a card that gives me the performance of a $50 computer).
 
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maikol

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Sep 15, 2025
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Thank you all very much for the responses and sharing your experiences and perspectives.

@ClassicHasClass
Your perspective makes sense and is a pragmatic approach. Beyond the collector aspects, one would have to "be there" to experience the speed up, particularly if this was part of the daily computing routine. Now might not make as much sense considering the financials.

@Trash80toG4
A full '040 would make a much better upgrade IMO."
Click to expand...
You mean an upgrade towards the 33mhz or 40mhz or one with an FPU?

@phipli
Thank you for the perspective and the link. Your sentiment of spending $500 for a $50 computer makes sense.
I have tried the version you are hosting on your website. I should try this one as well.
Question, overall, would it still make sense, if one acquires a 33Mhz part to overclock to 40Mhz? Or just wait.
 
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phipli

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Sep 23, 2021
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maikol said:
I have tried the version you are hosting on your website. I should try this one as well.
Click to expand...
The same version should be available in both places, but I'm more likely to forget to update my website than Macintosh Garden.

maikol said:
Question, overall, would it still make sense, if one acquires a 33Mhz part to overclock to 40Mhz? Or just wait.
Click to expand...
I would start by putting a 40x40mm self adhesive heatsink (something like these : https://www.aliexpress.com/item/1005004497885109.html or these : https://www.aliexpress.com/item/1005010143282437.html ) on your XC68LC040RC25 - some of my 25MHz parts happily run at 50MHz and they'll certainly work happily at 33MHz for now, and probably at 40MHz.

I think it is still worth getting a 33MHz part for piece of mind, especially if you don't care about having an FPU (only really used by professional 3D and audio software, and scientific research software - never games or home software that I know of) because you can buy the cheaper 68LC040RC33.

(Just in case you're not aware as some people don't realise, if you fit a 33MHz CPU, the computer will still by default, run at 25MHz - the speed is set by the board, not the CPU)
 
M

maikol

New Tinkerer
Sep 15, 2025
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Thank you. Good points and suggestions. I have one of those heatsinks lying around and I will put one on before and try the overclock. Hopefully it is not too tall and will fit in the case. Thanks for the tip, I will have it in mind that still a hardware change is needed even if the CPU is rated higher.
 
Trash80toG4

Trash80toG4

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Apr 1, 2022
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maikol said:
@Trash80toG4
You mean an upgrade towards the 33mhz or 40mhz or one with an FPU?
Click to expand...
Either one, not one for overclocking here, so sticking with 25Mhz would be fine, it's the FPU that counts. Q605 was first gen Quadra magazine covergirl, reviews noted that its 25Mhz 68LC040 outperformed IIfx 68030/FPU floating point performance, but full 68040/25 with FPU would be wickedlier faster.;)

I've kept my Q605/LC475 herd stock, concentrating on maxing out VRAM and upgrading memory. Baseline, first release QuadraCool does it for me. One thing I will say is that the jaunty angled LC475 support base for my Portrait Display is much better than the flat topped Q605.
 
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phipli

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Sep 23, 2021
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Trash80toG4 said:
Either one, not one for overclocking here, so sticking with 25Mhz would be fine, it's the FPU that counts. Q605 was first gen Quadra magazine covergirl, reviews noted that its 25Mhz 68LC040 outperformed IIfx 68030/FPU floating point performance, but full 68040/25 with FPU would be wickedlier faster.;)

I've kept my Q605/LC475 herd stock, concentrating on maxing out VRAM and upgrading memory. Baseline, first release QuadraCool does it for me. One thing I will say is that the jaunty angled LC475 support base for my Portrait Display is much better than the flat topped Q605.
Click to expand...
I suspect it isn't what you're thinking, but interestingly @Trash80toG4, only the CPU and PLL aren't rated for 40MHz on the LC 475. I've replaced both of them with 40MHz rated parts on mine, so my 475 is effectively upgraded to a 40MHz machine rather than Overclocked. Memory (RAM, ROM, VRAM) are all timed so that they're within specification at 40MHz, and the chipset is spec'd to 40MHz.
 
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phipli

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Sep 23, 2021
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Trash80toG4 said:
Interesting, so they used the same ASICs et al as on the 840AV? That was the only 68040/40 machine released. Where did your 475 component spec originate?
Click to expand...
The 475 and 575 use a chipset derived from the 650 / 800 chipset. They're all technically spec'd up to 40MHz.

There are datasheets floating around.

1766524299757.png
 
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