iMac G3 slotloader PRAM battery and overclocking

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GRudolf94
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iMac G3 slotloader PRAM battery and overclocking

Unread postby GRudolf94 » Fri Dec 22, 2017 12:33 am

Today I finally got around to opening my 400MHz G3 once again. I had decided to replace the leakage-prone and expensive 1/2AA for a CR2032, so I scavenged a holder from a dead PS3. You can see the result here:
FB_IMG_1513919240254.jpg
G3 mainboard


As it was already open, I figured, why the hell not overclock it?
Here's a close-up of the PLL multiplier select resistors, marked as PPC H/L, close to the VGA connector:
IMG_20171221_234012.jpg
PLL resistors


Pull-up resistors have 103 (10KOhm) marked on them, pull-downs are 102 (1K). I ended up getting a spare resistor from the modem (which I'll turn into a serial card, but that's another post)

Here's the settings table in case anyone else is feeling adventurous:
IMG_20171222_030638.jpg
PLL settings


And finally, the result:
received_1553731871328899.jpeg
About this Mac


A 400MHz G3 is almost guaranteed to make it to 500MHz, I wouldn't bet much on anything past that, especially considering they're passively cooled and already run a bit hot.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

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Irinikus
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Irinikus » Fri Dec 22, 2017 12:43 am

Very nice, it would be interesting to see if we could not modify our G4 CPU cards in the same way to get an overclock instead of having to go out and buy expensive SONNET ENCORE upgrades for the machines. (it would probably require a heatsink mod also in the case of the G4)
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GRudolf94
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby GRudolf94 » Fri Dec 22, 2017 12:46 am

Quick research shows it to be doable on G4's too. Requires a bit of a steady hand to solder 0603 case resistors, but doable anyway.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

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Irinikus
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Irinikus » Fri Dec 22, 2017 12:47 am

GRudolf94 wrote:Quick research shows it to be doable on G4's too. Requires a bit of a steady hand to solder 0603 case resistors, but doable anyway.


It sounds like a very cool future project! :D
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itsvince725
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby itsvince725 » Fri Dec 22, 2017 6:13 pm

I've got a 700MHz iMac G3 logic board, wonder how high that can go...there were iBook G3s that hit 900MHz.
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Raion-Fox » Fri Dec 22, 2017 10:05 pm

Regarding G4 over clock I have over clocked an MDD G4 to as high as 1.5 GHz but it isn't worth it. G4s are notorious for not only running hot but having cache miss errors as the speed increases so you trade cache efficiency for raw speed, and anyone can tell you that isn't a good trade.
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Irinikus » Fri Dec 22, 2017 11:39 pm

Did SONNET upgrade the cache on their CPU cards in order to reach higher clocks, without introducing the problem of cache misses?

I haven't played around with Apple at all (my machines are stock standard), but this could actually be a really nice learning experience, as the CPU modules for these machines are rather abundant and cheap as a result, unlike those found in SGI's.

If you were to increase the clock speed of a G4 CPU module, what would the optimum speed be? (Did Apple clock them optimally?)
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby GRudolf94 » Sat Dec 23, 2017 5:37 am

SONNET upgrades use chips spec'd higher. When overclocking, going one or two steps up is usually safe. When manufacturing chips, they are binned according to their reliability at a given speed, and then sometimes placed one bin below for a safety margin.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby GRudolf94 » Sat Dec 23, 2017 5:38 am

Also, Raion-Fox, did you try raising voltage on you MDD's CPU? Cache flakiness may be solved with a 0.05 or 0.1V increase (but I'd improve cooling while doing that)
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3

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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Raion-Fox » Sat Dec 23, 2017 8:58 am

Irikinus, yes, but not only that. The faster chips are laptop cores overvolted and stuck onto Powermac-compatible CPU cards. Performance wise they suffer from lower instruction density.

And GRudolf I do not advise overvolting a G4. It severely shortens their life even with sufficient cooling. The MDD G4s are already running close to the theoretical ceiling of the mainstream G4 CPUs.
:O3x02L: R16000 700MHz 8GB RAM kanna
:Octane: R12000 300MHz SI 896MB RAM yuuka
:Octane2: R12000A 400MHz V6 2.5GB RAM
:Tezro: Quad R16000 700MHz V12 8GB RAM murasaki
:Indy: (Acclaim) R4600 133MHz XL Graphics 32MB RAM
:Indy: (Challenge S) R4600 133MHz (MIPS III Build Server)

I am probably posting from yangxiaolong, HP Z230 with Xeon E3-1230v3, 16GB RAM, GeForce 750ti, and running NetBSD and Windows 8.1 Embedded.
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Irinikus » Sat Dec 23, 2017 10:05 am

Raion-Fox wrote:Irikinus, yes, but not only that. The faster chips are laptop cores overvolted and stuck onto Powermac-compatible CPU cards. Performance wise they suffer from lower instruction density.

And GRudolf I do not advise overvolting a G4. It severely shortens their life even with sufficient cooling. The MDD G4s are already running close to the theoretical ceiling of the mainstream G4 CPUs.


So at some point, I when I can get around to it, should I source the highest spec standard CPU modules offered by Apple for my machines? (not a huge priority though)
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby Raion-Fox » Sat Dec 23, 2017 11:40 am

The highest standard G4 is the dual 1.42 for the powermac G4. The fastest is the Powerlogix 1.42 due to faster and more cache.
:O3x02L: R16000 700MHz 8GB RAM kanna
:Octane: R12000 300MHz SI 896MB RAM yuuka
:Octane2: R12000A 400MHz V6 2.5GB RAM
:Tezro: Quad R16000 700MHz V12 8GB RAM murasaki
:Indy: (Acclaim) R4600 133MHz XL Graphics 32MB RAM
:Indy: (Challenge S) R4600 133MHz (MIPS III Build Server)

I am probably posting from yangxiaolong, HP Z230 with Xeon E3-1230v3, 16GB RAM, GeForce 750ti, and running NetBSD and Windows 8.1 Embedded.
Owner and operator of http://irix.pw

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GRudolf94
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Re: iMac G3 slotloader PRAM battery and overclocking

Unread postby GRudolf94 » Sat Dec 23, 2017 6:26 pm

IIRC the MDD runs the CPUs at 1.55V, and the MPC7455 datasheet addendum shows them as being able to go up to 1.85. I may be mistaken, though.

Anyway, a bit of overvolting might work, however I'd only risk it if I had a spare CPU module.
:Indy: R5000@180MHz, 256MB, XL-24, IndyCam
:Indigo2: R10K@195MHz in broken teal case with broken purple bottom, XZ Graphics, missing: RAM, drives/sleds, case bits, PSU; awaiting completion [ATX PSU CONVERSION IN THE WORKS!]
misc: Some Sun stuff, lots of x86 crap, one MSX and a MSX2+, a ZX Spectrum clone, slotloader 400MHz overclocked to 500MHz! iMac G3


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