Ok, tried briefly this morning 3x60MHz and 3x66MHz on air cooling.
--- 200MHz
One ADW CPU can POST at 3x66 + 4V, but no BOOT.
One ADZ CPU can BOOT. Needs 4V for that.
Both don't light up at 3V/5V.
No clock divider. Running 1:1.
System is not stable.
Looks like i will need a trimmer bolted on the motherboard to fine-tune stuff and eventually get things to a better place.
I am pretty sure that slapping a low-voltage Peltier on the ADZ CPU will get it over the finish line.
Will try that later today.
Why i didn't explore this early on ?
Looking back at the time when i was messing around with that stuff - the only ADZ processor that handles 200MHz well enough was throwing tantrums at 3x60 with anything but 3V. I guess this confused me and i decided that the CPU is flaky. But fresh look today gives me a different perspective - if the chip likes 200 at 4V and 180 at 3V only - so be it. That's how things are sometimes.
--- 180MHz
One ADW can do it at 3V.
One ADZ can do it at 3V.
One ADZ can do it at 4V.
No clock divider. Running 1:1.
System felt pretty stable, but eventually failed my favorite combo-grind-test: 3D rendering + VC6 code compilation + IE4 opening www.vogons.com + GlQuake 1 in Win95.
Low-voltage Peltier takes care of business for good.
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I am decently hopeful now that Chadti99's post about air cooling will prompt me to do some more tweaking and eventually move that 180MHz PC to 200MHz.
Let's see ...
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3x60 (180) vs 4x40 (160) - that is +20MHz to FSB.
3x66 (200) vs 3x60 (180) - only +6MHz to FSB.
The friction from 180 to 200 is much higher than 160 to 180.
So 180MHz is kind of the pivot point for 486 hardware overclocking.
But i get BitWrangler's joke 😉