Overclock LC475/P475/Q605 without soldering or spicy-o-clock

[killvore]

I took apart a Quadra 950 (PSU dead, RIP) and salvaged the 33MHz 040. Runs great at 40MHz in my LC475 - awesome work! Only thing is I couldn't get it to work in System 7.1 so I'm on 7.5.3, might take another run at it since 7.1 on a 40MHz 040 would just be blazing fast

 

[killvore]

I took apart a Quadra 950 (PSU dead, RIP) and salvaged the 33MHz 040. Runs great at 40MHz in my LC475 - awesome work! Only thing is I couldn't get it to work in System 7.1 so I'm on 7.5.3, might take another run at it since 7.1 on a 40MHz 040 would just be blazing fast

Got it working now! No idea why it didn't work earlier, just seemed like the setting wouldn't stick but it's happily cranking away at 40MHz under System 7.1 now (with appropriate System Enabler ofc)

 

[Callan]

Wrong post sorry

 

[Joopmac]

Hello all
Did some testing, did all the mods on a couple of freshly capped boards (swap the scsi resistor + the MC88916/20)
Result:
My diimo-less 475 runs at max 43mhz
my 'maxed' 475 with diimo can only reach 37mhz.

both boards have 60ns on-board RAM and 64MB of 60ns in the socket
the diimo-475 has 60ns VRAM and the 43mhz-one 70ns.

and now.. the speedometer 4.02 bench shows the 43mhz way faster than the 37 with cache... will posts the result later on

 

[Mustermann]

When you exceed 37/43MHz does the computer crash or show grafik artefacts or just does not run faster?

 

[Joopmac]

the normal one:
at >43 it crashes in finder or opening menus
at >44 at the normal 475 it crashes on loading the extension.

the bolle diimo-one:
at >38mhz with the cache card it crashes on loading the extension
at >37mhz it crashes with a bus error 10/bomb on loading the DIIMO extension

also another 475 with 68LC040 and original 88920, when you set higher then 40Mhz it just doesn't go higher indeed

 

[Mustermann]

One of my 475 devices is stable up to 50MHz (assume serial is not working), and crashes at 52MHz.
Configuration:
68040RC40
MC88916DW80
70ns internal RAM
60ns RAM module
60ns VRAM
55ns programmable ROM module

So you are lucky with 60ns internal RAM.
If you are able to compile the extension by yourself, you may try to change ROM wait state from 4 to 5 or more (to check if ROM is the limiting factor).

 

[Joopmac]

yes that's what i thought, but was surprised to see the maximum =)
i indeed also have the programmable ROM but it doesn't make a difference in crashing

unfortunaly i don't have the compiling skills =)

 

[feeef]

I just discovered this post and decided to give it a try on my LC 475. It was a success so far!

I just moved the resistor to R95 (didn't replace the MC88920 chip) and with a full 25MHz 68040, it was pretty stable at 40MHz. I joined my home network, browsed the Internet, downloaded, decompressed and copied some files, ran some benchmarks along with modelling and rendering with KPT Bryce for around two hours with no major issues.

I just had a few issues when changing the frequency on the fly. I first experienced a freeze of the system and a crash of the Finder another time when shutting off the Mac. However, when rebooting to the same frequency without changing it at any point, it seems to make everything pretty stable. I will see how it goes with time.

Not sure if I should invest in a proper 40MHz CPU? Such a bump in frequency may be a bit tough for my 25MHz chip?

Amazing discover and amazing job anyway! Thank you so much for the awesome work! My dream of having a 68040 machine @ 40MHz has come true!

 

[eharmon]

I just discovered this post and decided to give it a try on my LC 475. It was a success so far!

I just moved the resistor to R95 (didn't replace the MC88920 chip) and with a full 25MHz 68040, it was pretty stable at 40MHz. I joined my home network, browsed the Internet, downloaded, decompressed and copied some files, ran some benchmarks along with modelling and rendering with KPT Bryce for around two hours with no major issues.

I just had a few issues when changing the frequency on the fly. I first experienced a freeze of the system and a crash of the Finder another time when shutting off the Mac. However, when rebooting to the same frequency without changing it at any point, it seems to make everything pretty stable. I will see how it goes with time.

Not sure if I should invest in a proper 40MHz CPU? Such a bump in frequency may be a bit tough for my 25MHz chip?

Amazing discover and amazing job anyway! Thank you so much for the awesome work! My dream of having a 68040 machine @ 40MHz has come true!

What mask is the chip? https://eharmon.net/retro/macintosh/motorola-processors/#68040rc

 

[feeef]

@eharmon, my chip number is XC6840HRC25M so I guess the mask is either 2E31F or OE31F. Not sure what the difference is when comparing both lines.

 

[eharmon]

@eharmon, my chip number is XC6840HRC25M so I guess the mask is either 2E31F or OE31F. Not sure what the difference is when comparing both lines.

It still might be a D mask. The code is on the chip under the heatsink.

At any rate, the E masks will generally run fine at 40 if you’ve got the chunky heatsink on.

The 25 rated D masks can get quite hot and may crash, even if they boot.

 

[feeef]

Actually, @eharmon , it is not a HRC, it is a XC68040RC25M. Next to that it says 02E31F. Not sure how you determine if it's a E or a D mask from that?

So far it has been running pretty stable at 40MHz. I had a single crash when it was @33MHz but I am not sure if it was the software that didn't like me changing the CPU speed on the fly.

 

[eharmon]

Actually, @eharmon , it is not a HRC, it is a XC68040RC25M. Next to that it says 02E31F. Not sure how you determine if it's a E or a D mask from that?

So far it has been running pretty stable at 40MHz. I had a single crash when it was @33MHz but I am not sure if it was the software that didn't like me changing the CPU speed on the fly.

02E31F; the E masks all have the smaller geometry, which usually runs cooler, all other things being equal. That'll probably run fine at 40, then. But you'll want to let it run for awhile to see if it overheats or if you need active cooling, if you want to keep it at 40 long term.

 

[feeef]

Thank you very much for the tips @eharmon ! I will keep testing. It's joy using that computer. So much I can do with that machine!

I am a graphics designer and I sometimes still do some work on my PM 9500. This makes me want to try a few things on the LC 475 as well. Especially animations with basic 3D and Director for 2D. I also have to try some retro style video editing and compositing on a 40MHz 040!

 

[zigzagjoe]

If you want 40mhz in 24 bit mode, here you go. This will work in either 24 bit or 32 bit mode correctly; it wraps the register pokes in SwapMMUMode as I previously described in this thread. Otherwise it is functionally the same, it switches to 40mhz as early as possible in the boot process.

I was going to try to be nice and add checking gestalt so that it'd not cause bus errors on other systems (that the extension is not for) but THINK C is being a wiener and I don't feel like figuring out why.

 

[MacinJosh]

Those of you running 48MHz+ (especially 50MHz+), using the extension, are you doing that with a network connection? Aka, are you loading the Open Transport "Shared Library Manager" that loads up the Open Transport Libraries?

In my experience with an LC475 and Mystic Color Classic, the system will hang right after loading the Shared Library Manager, which happens immediately after loading the Soft 475 Overclock extension, making it seem like it's the overclocking extension that's locking up.

On my LC475, the fastest system I can configure based on benchmarks is 39MHz with min & max at "1" + DiiMO 040 Cache enabled. It's rock steady and super fast.

However, if I load Shared Library Manager, it will hang. In fact, the only speed it will not hang in with min & mac at "1" is 34Mhz.

As a compromise, I am now running 45Mhz with min & max at "2" without DiiMO 040 cache as it won't work with frequencies over 40Mhz. It's close to the 39Mhz above but not quite.

My Mystic will actually run at 47Mhz with min & max at "1" without Shared Library Manager which is super fast. I am still trying to find the highest speed that Shared Library Manager will load with min & max at "1".

So far the Mystic will load Shared Library Manager at 47Mhz with min & max at "2", which is pretty nice.

For those wondering, the CS overclocking, even at 50MHz (which both systems run fine with networking), is not even close in terms of graphics and disk performance to 39MHz + DiiMO with min and max set to "1", and barely edges out in CPU and FPU performance.

 

[Joopmac]

That is interesting as I benched the 43mhz non-diimo as faster then 38mhz with diimo

 

[MacinJosh]

That is interesting as I benched the 43mhz non-diimo as faster then 38mhz with diimo

You haven't mentioned whether you use Custom or Advanced. If you're using Custom, then yes, 38MHz with DiiMO should be around the same speed as 43MHz without DiiMO (DiiNo ) simply because by default 38MHz has a Min of "2" and Max of "3" while 43MHz has Min & Max both at "3". But if you go down to Min & Max "1" at 38Mhz... well, see for yourself.

 

[Joopmac]

Oh that is interesting
No, I never touched advanced
Will try and post results