Date: Sat, 7 May 2005 00:29:53 +0100 (BST) From: Daniel Price <[EMAIL PROTECTED]> Subject: Re: [1st] Radius 81/110 (8100) Troubleshooting
I did as you said - I removed the motherboard, and the heat-sink and examined the CPU. No cracks - it actually looks like it was made yesterday. I did notice that there was a LOT of dust and fluff on the board though.
I cleaned the sockets, fiddled with the ROM card and got rid of as much dust as I could. But still no luck. But boy does that 601 heat up fast! Surely, if it was a heat issue, the mac would at least get through a POST and begin to start, even if only to crash later.
I've had heat related problems with other machines I've clocked-chiped. But this is damned weird. I guess I could just pick up an 8100 board and replace the whole thing. The only difference between them (I think) is that the Radius has a standard mac monitor connected, as a opposed to the silly composite thing on the other x100s.
Right down to the surface mount cap and resistor placement, the boards are identical except for the DRAM video connectors.
I also mostly think that the machine would manage to POST and chime before overheating, however, the 110 MHz PPC601 heats up really really fast. That is why there is a Peltier cooler on the heat sink (or should be).
IBM actually only rated the PPC601 for 100 MHz operation and specified that operations from 100 - 120 MHz required keeping the chip below some temperature which I don't remember. Basically, anything above 100 MHz requires more heroic cooling measures, so it is conceivable that a 110 MHz PPC601 heats up so fast that it can't POST.
Anyway, if you clean up the old heat sink compound (which is probably more like a powder than a paste at this point) and replace it with fresh, and properly replace the heat sink, that should solve that question.
Do not overapply the grease. It just takes a tiny dab. You are just filling in the spaces between the CPU die (little metal square) and the heat sink surface which arise because neither one is perfectly flat. As you can imagine that should require very little heat sink grease. I once ruined a PPC601 by applying too much grease and it ran onto the CPU pins and shorted some out--zinc based compounds can be conductive.
Oh, one other test--turn on the machine, with the heat sink wires plugged in to the motherboard (assuming you do have the peltier cooler, as you should) but with the heat sink hanging loose. The CPU side of the heat sink should become noticeably cool. Don't run it like this for more than 30 seconds or so, since you don't want to overheat your sinkless CPU.
Before my first message, I did not notice that you were in the UK. I guess you may not have Radio Shack there. The heat sink grease they sell is their own brand. I imagine that any well stocked PC shop in your vicinity will sell something similar, though perhaps more dearly.
Arctic Silver brand heat sink compound is the deluxe stuff, but it is about $15 per tube, and there is just no reason to use it for this application when a regular zinc based compound will work fine at 1/5 the price. Unfortunately, Arctic Silver may be the brand that you can most commonly find in PC shops. If you have a radio hobbiest type shop or any shop that sells soldering supplies they are also likely to have a zinc based heat sink compound at an affordable price.
Anyway, if the CPU isn't cracked, and if it isn't overheating--that may yet be the problem--then I am out of ideas. You've tried the thorough trouble-shooting technique--Unplug everything, swap what you can on a minimal hardware setup, see if it works.
I will tell you that on the 7100 I have seen several machines which were overheating because of aged heat sink compound which had gone to powder. They would POST and chime but locked up very soon thereafter. The 7100 doesn't go faster than 80 MHz. So it is conceivable that an 8100 clocked at 110 MHz might overheat its CPU before it can chime. Replacing the heat sink compound, after cleaning, fixed each of those 7100s.
Jeff Walther
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