This board seems not to be in working condition but looks very nice. You should not modify / destroy it for your soldering practices. Look out for a board in a worser condition for your exercises please 😉

Board is 100% working, I'm using it right now. It wasn't populated in the image with CPU/Bios/etc because Liqmat was cleaning it at the time 😜

What could possibly go wrong replacing the clock crystal? I have years of experience soldering.. if it's through hole it's a quick and easy job. I'll even add a fan over the components for good measure when I'm done 😜

One thing to keep in mind is that changing the CPU clock will likely change the ISA bus speed and ram timing. At 24Mhz /2 for cpu and /3 for ISA so going to 32Mhz (for say a Harris 16mhz cpu) will put the ISA at 10.6 which most GOOD vid and IDE cards should handle but you would probably have to add get faster ram if there is no Wait State jumpers to add. Yeah the 12Mhz xtal is most likely for the co-processor, they can run Async. The 14.318 Mhz xtal is for CGA/MDA cards timing thru ISA bus (VGA have there own xtals), and there should also be a micro 32.7 Khz micro Xtal for cmos and RTC if you didn't have the Dallas RTC chip. Sorry just rambling on as I have done similar with 386sx boards in the past :p

Horun wrote:

One thing to keep in mind is that changing the CPU clock will likely change the ISA bus speed and ram timing. At 24Mhz /2 for cpu and /3 for ISA so going to 32Mhz (for say a Harris 16mhz cpu) will put the ISA at 10.6 which most GOOD vid and IDE cards should handle but you would probably have to add get faster ram if there is no Wait State jumpers to add. Yeah the 12Mhz xtal is most likely for the co-processor, they can run Async. The 14.318 Mhz xtal is for CGA/MDA cards timing thru ISA bus (VGA have there own xtals), and there should also be a micro 32.7 Khz micro Xtal for cmos and RTC if you didn't have the Dallas RTC chip. Sorry just rambling on as I have done similar with 386sx boards in the past :p

I believe I see one more crystal in the pic right next to the AT power connectors (re: CMOS). I haven't seen the board myself yet, it was gifted to me in a nice AT case which I've been using. This is just a future plan to do some modifications.

So if what you're saying is correct re -ISA speeds at 1/3 of xtal, it would be impossible for me to run anywhere above 16mhz. 16mhz would still be a quite significant lift for this machine anyway. 20mhz would require 13~mhz ISA and 25mhz forget it (~17mhz). This board does indeed have a wait state jumper according to the manual, I can set it to 1WS if need be.

Did later 286 boards that were capable of running the 25mhz chips have additional clock dividing circuitry or yet another xtal? Surely they aren't pushing the ISA bus that far.