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6100/G3: cranking up the system clock, is 80MHz possible?

greystash

Well-known member
I have a Power Mac 6100/60 with a G3 upgrade upgrade card and have been trying to figure out how to increase the Bus speed after an interesting comment from @Trash80toHP_Mini. In the past I believe this was achieved by either replacing an oscillator with a higher frequency replacement, or by using something like a RocketSocket.
All information that I've come across states that you can achieve a CPU increase to 80/82MHz with a 40/41MHz oscillator and increased bus speed.
I have a basic knowledge of electronic components but I haven't been able to Identify the oscillator in question on my machine. I've done some searching but I haven't found any images of how the upgrade is performed, it's only been described. There doesn't seem to be much information left about the RocketSocket!

Is anyone able to point me in the right direction/show me the oscillator that should be replaced.
 

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greystash

Well-known member
A better quality image of what looks like a 30MHz SMT TTL Crystal Oscillator. If this is the correct oscillator, would the second image be a suitable replacement?
 

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Phipli

Well-known member
Yup, the 30MHz clock (yes, that is an SMD Clock) looks like it is the bus clock for your 60MHz 6100.

Are you comfortable replacing it? Alternatively you could use a clip kit - these disable the built in clock and inject their own by just attaching to the top of the clock.

The majority of 6100s will do 80MHz, but not all. If you want hot weather reliability when you boot from the 601 you might consider going with something around a 38MHz clock? I have multiple partitions on my 6100 - some with and some without the Sonnet extension. Without the extension the computer just boots as a 601. The same can be achieved with extensions manager (make sure it loads before the sonnet extension and hold space during boot.

Have you removed the logic board cache?
 

Phipli

Well-known member
You haven't shown enough of your proposed replacement to tell if it is the right package. There are multiple similar parts in different size cases.
 

greystash

Well-known member
Yup, the 30MHz clock (yes, that is an SMD Clock) looks like it is the bus clock for your 60MHz 6100.

Are you comfortable replacing it? Alternatively you could use a clip kit - these disable the built in clock and inject their own by just attaching to the top of the clock.

The majority of 6100s will do 80MHz, but not all. If you want hot weather reliability when you boot from the 601 you might consider going with something around a 38MHz clock? I have multiple partitions on my 6100 - some with and some without the Sonnet extension. Without the extension the computer just boots as a 601. The same can be achieved with extensions manager (make sure it loads before the sonnet extension and hold space during boot.

Have you removed the logic board cache?
Thanks @Phipli!
I think I could replace it, I'm reasonably confident with soldering and have a heat gun too, but a clip kit may be a better option. Where would I find a suitable clip kit for this?

Thanks for the advice on multi-booting. I noticed this when trying to get the HPV card going, I do need to make sure extensions manager loads first though!

Yes I have removed the cache, I heard that in some cases it can slow the accelerator down so only the ROM is present now.

Ah sorry about the replacement image. I found it on eBay, I couldn't find this piece on Mouser but maybe I was searching for the wrong thing.
 

Phipli

Well-known member
Ah sorry about the replacement image. I found it on eBay, I couldn't find this piece on Mouser but maybe I was searching for the wrong thing.
Those look right although are you sure you want 40? :ROFLMAO:
I think I could replace it, I'm reasonably confident with soldering and have a heat gun too, but a clip kit may be a better option. Where would I find a suitable clip kit for this?
They turn up on ebay sometimes, but it might be easier to make one. You need a clip that fits over the clock and shorts pin 1 (enable) to ground (pin 2) to inhibit the clock, then inject the 40 MHz clock on pin 3. You can get power from pin 4 (5V and pin 2 for ground).
 

Trash80toHP_Mini

NIGHT STALKER
Well this is really good news. Looks like my 6100/60 case has a 66MHz board installed. Had figured that because the 33MHz crystal was the only value that made sense. No signs of rework, is there any other differentiation between the 60/66MHz boards?

Clip/40MHz Crystal sounds like the way to go for my experimentation, has anyone got a link to the proper part?

My machine has both ROM DIMM and possibly a Cache DIMM, I think I know which one was in the ROM slot, but they seem almost identical. I may have mixed them up? Which is which or are they the same thing?

6100-DIMMs-00.JPG

6100-DIMMs-01.JPG

If they're the same, that cannot possibly have been good.
 

Phipli

Well-known member
Well this is really good news. Looks like my 6100/60 case has a 66MHz board installed. Had figured that because the 33MHz crystal was the only value that made sense. No signs of rework, is there any other differentiation between the 60/66MHz boards?

Clip/40MHz Crystal sounds like the way to go for my experimentation, has anyone got a link to the proper part?

My machine has both ROM DIMM and possibly a Cache DIMM, I think I know which one was in the ROM slot, but they seem almost identical. I may have mixed them up? Which is which or are they the same thing?

View attachment 47483

View attachment 47484

If they're the same, that cannot possibly have been good.
Erm... you have two ROMs?! At least you don't have two cache cards, that would be worse.

It doesn't matter which slot the ROM and cache go in. They work in eithee.

You want to get a cache for it (unless you plan to use an upgrade in it). They make a decent difference.
 

Trash80toHP_Mini

NIGHT STALKER
So they're both ROMs? I wonder which is the correct one for a 66MHz 6100? I don't need Cache as I have something like three Newertech and a couple of Sonnet G3 cards to try to get this thing up and running on an 80MHz system bus.

Service Source clearly labels ROM slot as next to PDS and Cache slot inboard the ROM? I'd think they'd be wired for different addresses? Gotta look at the DevNote I guess. Anybody got a link handy?
 

Phipli

Well-known member
So they're both ROMs? I wonder which is the correct one for a 66MHz 6100?
They're both the same. Exactly the same.

Service Source clearly labels ROM slot as next to PDS and Cache slot inboard the ROM? I'd think they'd be wired for different addresses? Gotta look at the DevNote I guess. Anybody got a link handy?
Like I said, in first gen Nubus, the ROM and cache can be switched with no impact on behaviour / performance.
 

bakkus

Well-known member
Be aware that depending on your G3 accelerator (which is mentioned in the title), adding L2 cache to the motherboard might be detrimental to performance.
Some Sonnet Nubus G3s come with some onboard L2 cache, which is _much_ faster than the stock one which is meant for and wired up to the PPC601.
If it can somehow be convinced to degrade it to L2 cache.. maaaybe?
 

Trash80toHP_Mini

NIGHT STALKER
Onboard cache would be sleeping along with the 601 given G3 card on board. Can't imagine getting it to run as L3 asynchronously at only 30-40MHz or wanting to? Did any mfr. ever attempt that? Bad enough main memory is on the pokey System Bus. L2 on accelerators operating at the processor card's native clock is tasked with minimizing the performance hit from the bottleneck of accessing system memory..

Yes the ROMS have Apple markings... I have some chace for 6100 if needed. Cache goes closer to CPU.
Thanks much, but none needed for my build. As I said, I have a handful of Newertech and Sonnet G3 cards in 6100 form factor, all with 512K Cache or 1MB on board.

The question is getting one of the G3s up and running in a 6100 that thinks it's an 8100 with 80MHz system clock. Most of the clock chipping limitations Mark Shrier assembled has to do with running the OEM CPU outstripping the performance envelope of subsystem as are bus multiplier concerns for both brands of cards. Complications there are documented in the earlier thread.


Theory here would be that the 6100 shared the subsystems with its faster 7100/8100 stablemates. Nothing else makes sense to me form an economies of scale perspective. The 6100 is sufficiently hobbled to low end status by the CPU. We'll see!
 
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choongng

New member
I have a 6100 with the piggy back crystal for 40MHz bus + a Sonnet G3 card (I think it selects 220MHZ when the bus is 40MHz). Haven't booted it in a while but it worked great for years in that configuration.
 

Phipli

Well-known member
Onboard cache would be sleeping along with the 601 given G3 card on board. Can't imagine getting it to run as L3 asynchronously at only 30-40MHz or wanting to? Did any mfr. ever attempt that?
On Nubus Macs you have to remove the logic board cache when you install a G3 upgrade. It doesn't not matter, I forgot once and the machine was very unstable.

Where the L2 cache was soldered on some 9600s, upgrade manufacturers had problems, so some made it so the upgraded machine continued to use the logicboard L2, and used the upgrade's cache as L3. This resulted in lower performance, but the alternative was soldering to disable the logicboard cache.
 
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joshc

Well-known member
The thing I'd worry about with overclocking anything in 6100 is the heat. The 6100 does not have a good thermal design, the stock 601 can overheat.
 

Trash80toHP_Mini

NIGHT STALKER
I was looking into that when adapting it to use the too long HPV card on the accelerator. Air vents in from under the HDD and was wondering about installing a centrifugal blower under the HDD shelf, to overpressure the system as opposed to simply drawing air through the bottom vent in the stock scenario.

Was also wondering about any performance differences between the A/V and HPV/2MB cards. A/V card has 2MB VRAM installed as well. Unless some memory is reserved for A/V ops, there should be no point in using anything but the 8100's high end HPV/4MB config in the 6100, no?
 

Phipli

Well-known member
Was also wondering about any performance differences between the A/V and HPV/2MB cards. A/V card has 2MB VRAM installed as well. Unless some memory is reserved for A/V ops, there should be no point in using anything but the 8100's high end HPV/4MB config in the 6100, no?
I think I remember reading performance was the same between AV/HPV2/HPV4.

As you say, I think the 7100 AV card is basically pointless as you might as well have an AV card. The 4MB cards have gone really hard to find weirdly. Not sure why.
 

Trash80toHP_Mini

NIGHT STALKER
At 2/4MB they were a high end option supporting more/better pixels on big displays, which was still a premium niche segment of the user base. If the best you had was 16" CRT display resolution there was no real need for more than 2MB of VRAM.
 

jeremywork

Well-known member
On Nubus Macs you have to remove the logic board cache when you install a G3 upgrade. It doesn't not matter, I forgot once and the machine was very unstable.
Interesting... I have a few 8100/100s with Sonnet G3s and had always removed the cache per the installation manual's directive until one of them shipped in with the cache and G3 both installed, so I tested it for a while and didn't notice any instability. I've since added the cache back to a second 8100 and haven't noticed problems there either; didn't seem to affect performance numbers either. I'd advise sticking with the recommendation, but seems like something should explain why yours is less stable than mine seem to be.

Also,

I believe 2MB/4MB HPV cards use a 64-bit memory bus and should perform identically (limited by VRAM amount.)

A/V or VIVO cards use only a 32-bit memory bus and will dedicate half of their 2MB to video input when in use. Because of the 32-bit bus it's a bit slower than the HPV models (guessing it's due to using Quadra AV susbystem parts?)
 
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