I have An Eyetech A1 XE with a G4. It says MPC 7441/7451 . It used to be my back up machine, but since my main A1 bit the dust it is all I have. It is very unstable when it is hot. This spring I had a new cpu cooling fan (Iceberq 4 pro) installed, but it hasn't really helped. I have had to resort to using Win UAE over the summer, but now the laptop I had that on is having problems. This all brings me to my question I seem to remember hearing that the cpu clock can be reduced on a G4 to help with overheating. I downloaded the manual, but I still don't know how to set the jumpers. It should be either JP11, JP12, JP13:
Set the system clock configuration. orJ17, JP17: Core voltage switch or maybe both? Has anyone under clocked an A1 and what jumper settings did you use?

@wisementrading.com

This thread on AmiBay.com may help. Contains also link to A1-XE manual on intuitionbase.com.

Slightly off topic. I under clock my Blizzard 1230 mkiv to 33MHz so it runs cool as can be, still retaining enough horsepower for my use.

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@pavlor

Thanks.

I had found the manual on intuitionbase. So only the system clock needs to be changed and not the core voltage?

It looks to me like there are only 2 choices of either 133mhz or 100mhz since the manual says that the jumper on the cpu card can be ignored for mpc74xx.

Last edited by wisementrading.com on 25-Sep-2016 at 09:18 AM.

@wisementrading.com

If understand this right, changing system clock (eg. to 100 MHz) lowers also CPU-clockrate (which is multiplied). Or you can retain system clock and change CPU clock multiplier. Lowering system clock seems to be safe solution.

@wisementrading.com

You should probably test the bus clock reducing to 100MHz first.
Let it run for a few days.

I learned the hard way that the southbridge on Eyetech boards were *very* picky about the bus speed and connected drives.
I even got read/write errors on a drive that *did* do 133MHz, southbridge wasn't capable though.
Went back to using 100 MHz and all was fine.
Maybe that is all you need to do to make it stable again.

Don't tinker with the cpu clock rates until you're sure you have too...too many people fried their cpu...

Good luck

@wisementrading.com

That sounds like someone has previously upped the system clock setting anyway.
Mine runs OK and I have never changed the jumpers from the 100MHz setting. They were supplied underclocked to 800 MHz CPU speed with a flimsy fan - again, mine is at the original setting, even still has the original fan and I´ve never had an overheating problem.

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@wisementrading.com

You've gotta be careful when you change those settings. As no doubt you would be aware. How old is your PSU?

My A1 used to be very unstable. I don't know if the G3 is more stable than the G4. But the G4 does use more voltage so certainly can run hotter.

I did play with those dangerous settings once and lowered them in attempt to stablise my machine. It didn't work.

What did work for me was replacing my PSU and setting my CPU settings correctly. That is 133Mhz FSB. And 800Mhz CPU speed.

My machine has been very stable since. There is the occasional freeze. Sometimes games do crash earlier in summer. And CPUTemp gets very annoying. But it's as good as it gets.

@Hypex

Weren't some of the early G4 systems shipped with slightly incorrect voltage settings. I wasn't having any problems but changed it to what was recommended at the time anyway. I ran a 133Mhz system clock with no problems.

@wisementrading.com

The Iceberq 4 pro looks nice but I went for something a bit beefier when I switched from the stock cooler. I also swapped the nylon screws that hold the module in place for steel nuts and bolts with nylon washers. It's also a good idea to sleeve the bolts so the module sits in the socket perfectly. This can be done with additional nylon washers.

@wisementrading.com

The JP17 (?) selects the BUS speed (100 or 133 MHz). The CPU speed is a multiple of that, selected by the DIP switches on the CPU board.

The easiest way to slow it down is simply to change from 133 to 100 MHz (JP17). The CPU clock speed will reduce by the same ratio. If you then want to restore the CPU speed while leaving the bus speed at the lower rate, you will have to adjust the DIP switches.

I can't remember the settings, sorry. They are well documented in several places.

You may also find it beneficial to remove and clean the edge connectors of the RAM DIMM. A very few people have managed to get an XE to run reliably with two DIMMs, but most machines can only tolerate a single one. You won't get better than a single 512 MB DIMM.

The core voltage should not have to be altered if you are reducing the CPU speed. It is critical and was supplied set to a low value in an effort to reduce heating with the toy heatsink that was originally fitted. If you have a proper heatsink, you should check the setting of the core voltage switches (in the back of the manual). You might find that they are still set to a low value.

Don't change any of the switches while the system is powered up - you can damage the CPU in an instant.

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tony

Hyperion Support Forum: http://forum.hyperion-entertainment.biz/index.php

@Rob

ISTR there was some discrepancy between the Vcc table and what Vcc was actually set. Now if anything it should have been lower if different to avoid over heating. Of course if the CPU wasn't being feed the Vcc it needed then it could go unstable and start freezing or random crashing.

And that's another thing I checked. As well as proper setting for FSB and CPU clock I also set the Vcc to the specified amount for my CPU.

@tonyw

What about a 1GB DIMM?

@all

Thanks for all the suggestions. I am giving them a try one by one. So far it is a no go on changing the BUS speed when set a 133 MHz the UBoot screen says mpc2450 866MHz which is what I have been running at. When the BUS speed is set at 100MHz it says 650MHz, but the machine hangs at various stages before getting the kickstart all the way loaded. According to the manual the BUS speed is changed by jupers on JP11, JP12, JP13. The Core voltage is changed by the dip switches on J17 and JP17 is always shorted.


Funny thing is the manual only talks about a 7451 and not a 7450 also when I run the cpu command from a shell I get MPC 7441/7451 so maybe I really do have a 7451.


I have a new(er) power supply so next I will see if it will fit and give that a try. I am also looking for nylon washers as that sounds like a great idea. I know this has been dealt with several times before, but any suggestions on a (hopefully currently available) heatsink/fan would also be appreciated.

@wisementrading.com

I forgot to say I do know it is a heat issue because the only way I can keep it stable at all (if you can call it that) is by removing the side of the case and placing a large fan blowing directly on the motherboard and CPU cooler.

@wisementrading.com

Quote:

I know this has been dealt with several times before, but any suggestions on a (hopefully currently available) heatsink/fan would also be appreciated.

The Zalman VF900-CU cooler was a common choice for people looking to fit proper cooling to their A1-XE G4s. I did it with mine, and the temperature as read by the CPU docky dropped from 50-60 down to around 30 degrees C, which is a very comfortable temperature for a CPU. You'll need to use slightly different bolts or modify the ones it came with, but it's well worth the effort.

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@wisementrading.com

Quote:

so maybe I really do have a 7451.

A1-XE was delivered with 7451, 7455 and 750FX CPU modules.

Quote:

So far it is a no go on changing the BUS speed when set a 133 MHz the UBoot screen says mpc2450 866MHz

Standard frequency for 7451 in A1 was 800 MHz (if my memory serves me right), your CPU seems to be over-clocked (explains stability issues).

@pavlor

Yes 800 for G3 as well. I recall there were some 933 chips or that was on there after the "cover" was the taken off so underclocked.

@Hypex

Quote:

Yes 800 for G3 as well. I recall there were some 933 chips or that was on there after the "cover" was the taken off so underclocked.

Yep later boards shipped with a 933Mhz G4 but was underclocked to 800Mhz. Alan said because the advertised speed was 800 but seeing as Eyetech were from Yorkshire, it may have just been that they were too tight fisted to buy better coolers.

If wisementrading is about to reseat the CPU module, take a really good look at the way it sits. The original nylon spacers were too short, with the result that the CPU module sat crooked and sometimes did not make proper contact with the mobo connector. IIRC the spacers were 5.5 mm but should have been 6.0 mm.

I would take the mobo out of the case and check it carefully - cut new spacers with a sharp knife or add some packing under the old spacers, but get it straight and that's one failure mode out of the way.

I wouldn't go buying a new PSU - it's unlikely that a PSU would fail at higher temps, but if you already have one to try, then that rules out something else.

I've never seen a 1GB module in that form factor, but it should be good if you can get one.

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tony

Hyperion Support Forum: http://forum.hyperion-entertainment.biz/index.php

@Rob

They were definitely tight fisted. There was probably a few stories about this circulating but my original A1 XE board CPU fried. It was originally shipped with only plastic or nylon nuts holding the fan to the CPU module. I was testing it out with the board laid flat. I turned away for a moment and then I heard this whizzing sound from the fan. I turn back and half the fan has broken loose! I reach for the power switch but the moment was gone. Like the fish in that Simsons episode it was gone before it hit the ground. In those few seconds, just the fan coming detached from the CPU was enough for the CPU to fry.

I was fortunate I got a replacement under warranty. I'm sure along the lines blame would have been put on me. But I had the board flat and I didn't attach the fan or modify it. Perhaps the nuts became unstable during transit. But to find it just flew off like that after little use was shocking. It didn't prove to be good for the PPC either, which was a Motorola, if the CPU failed to detect a heat surge and shut it self off.

When my replacement came I saw they now used metal nuts and bolts to hold it down. So it was a lot more secure. I took it as judgement at the time, put in place to stop me causing my fan to come off again. But perhaps by then they knew it needed to be more secure. I don't know of any other cases where this happened. But for Eyeyech this would have been costly. And we see how even secured fans included were not the best choice.

Last edited by Hypex on 27-Sep-2016 at 05:29 AM.