How far can one overclock a 10MHz 80286. :)

[stamasd]

Well I found that out during the repair of a motherboard. I was trying to reverse engineer a small board attached by a cable to the motherboard, which turned out to be the CPU oscillator. So of course I had to see if I can replace it with something else, and for that I busted out a signal generator. The CPU on this particular motherboard seems to have been factory overclocked, since the original oscillator was 12MHz. And this is how far I managed to push it and it still worked.






25.3MHz.
Over 100% over the factory overclock, or over 150% from the chip's rating.


(BTW, the motherboard is a Wyse-2200-01 https://theretroweb.com/motherboards/s/wyse-wy-2200-01-819711 and the oscillator is attached to the 6-pin header located between the CPU and the coprocessor socket)

And the original oscillator board, which used a 60MHz oscillator and divides it by 5:

[i440bx]

The CPU has an internal /2 divider for the clock signal.

Means if you feed it with 25MHZ the CPU run's at 12.5MHZ.

So you overclocked the 10MHZ CPU by 25% to 12.5MHZ.

There was a factory underclock of 4MHZ, as the Oscillator feeds 12MHZ and the CPU runs at 6MHZ.

[stamasd]

Shit I forgot about that.

[Williac]

Things like this are what keep me reading all the posts on this site. Awesome stuff.

I don’t really miss having to manually calculate my CHS+LZ on a HDD, or do division to calculate FSB and RAM timings for an overclock just to make things work. But as a hobby? Oh yeah.