double post

Ok clear, so if there is two of them i replace both?

With these?

https://i.postimg.cc/6t1Dv0XB/IMG-2507.jpg

Or these?

https://i.postimg.cc/fM0sBFzH/IMG-2508.jpg

Also can i get higher mhz? Eg 40mhz?

I wouldn't go higher than 25MHz. There are 12.5 MHz clocked 286 CPUs, it could be feasible.

Both your pictures are 4-pin, so either is good.

Sorry why not?

I would like to get 32mhz oscilators so i can use 16mhz 286 chip.

Hey, maybe you're lucky and the whole system stays stable. Who knows. 🙂

Omarkoman wrote on 2025-05-29, 10:47:

Sorry why not?

I would like to get 32mhz oscilators so i can use 16mhz 286 chip.

Because many things on the motherboard are working synchronously to CPU.
It was not uncommon back in the day to have many onboard clock signals derived from single oscillator by simple dividing. So when you increase the CPU clock speed - many things at once receive proportionally faster clock speeds, and those many things were not built for that new speed. You want to triple the CPU speed, but all the other ICs can't run 3x faster than they were designed for. You can find yourself a 25 MHz CPU, but you're not replacing the rest of the discrete ICs.

Will anything get damaged if i go with 32mhz/16mhz set?

Also, can i have higher oscilator and slower cpu? Eg 32mhz but get 12mhz cpu?

Omarkoman wrote on 2025-05-29, 10:47:

Sorry why not?

I would like to get 32mhz oscilators so i can use 16mhz 286 chip.

The Chips & Technologies 8220 chipset is not designed to operate at frequencies above 10MHz (from a 20MHz crystal or oscillator). Everything above 10MHz is overclocking. 16MHz is 60% overclocking, which is unlikely to succeed. 25/12.5 sounds like being worth a shot, though. The 8220 chipset is unable to operate a different frequency than the processor. It's not until the 486 processor that we got typical PC processors that run internally at higher speeds than the chipset.

Furthermore, everything runs at fixed ratio on your system. Running the processor at 16MHz with a 32 MHz oscillator would also run the ISA bus at 16MHz and the DMA controller at 8MHz, again overclocking all that stuff as well. Furthermore, the chipset will not add extra wait states to ISA cycles at higher clocks, so ISA cycles are shortened below their typical durations, which will impact cards that do not add wait-states theirself.

If you want to run a high-end 286 system (16 or 20 MHz), you should definitely get a mainboard that is designed with clock rates like that in mind. The board you currently have is meant for 6 to 10 MHz, not for 12 to 20 MHz.

Omarkoman wrote on 2025-05-29, 11:04:

Also, can i have higher oscilator and slower cpu? Eg 32mhz but get 12mhz cpu?

In that case, the CPU (that should work properly at 12MHz) tries to operate at 16MHz. The likely effect is that the system will behave unstable and not even pass the POST.

Ok i found a 12mhz cpu and 24mhz oscilator so will give that a try.

Will report back once i get all the parts.

Thanks all for the input, i learned something new today.

Omarkoman wrote on 2025-05-29, 11:04:

Will anything get damaged if i go with 32mhz/16mhz set?

Probably not without leaving it like that for a significant duration of time.
No guarantees though, if the behavior logic is borked by inappropriate speeds - multiple driving ICs will fight, pulling the signals into opposite ways.
It will handle the short runs, but will be damaged in the long run, and nobody could predict the exact definition of that "long".

Omarkoman wrote on 2025-05-29, 11:04:

Also, can i have higher oscilator and slower cpu? Eg 32mhz but get 12mhz cpu?

Depends entirely on the design of the clock trees on the motherboard. If you don't have any jumpers for clock dividers, no PLLs - there's nothing you can do about relations between speeds, it will be a direct proportion defined by the motherboard design, _everything_ will scale up with that replaced oscillator, and _everything_ must be able to handle that speedup percentage.

Note that _everything_ includes the ISA bus and the cards plugged into slots.

quick update, interestingly, I found the sales flyer that came with the PC in which the motherboard was in and it says, turbo function is available using the keyboard to switch between 6 and 10mhz.

Anyone heard of this before and what would be the key combination to switch the modes?

Omarkoman wrote on 2025-05-30, 21:30:

quick update, interestingly, I found the sales flyer that came with the PC in which the motherboard was in and it says, turbo function is available using the keyboard to switch between 6 and 10mhz.

Anyone heard of this before and what would be the key combination to switch the modes?

Keyboard combinations were very common those days. The most common one is Ctrl-Alt-Num+ for high speed and Ctrl-Alt-Num- for low speed.

oh cool! will give it a go ! thanks.

Omarkoman wrote on 2025-05-30, 21:45:

oh cool! will give it a go ! thanks.

Maybe there is a jumper for Turbo on motherboard?

Omarkoman wrote on 2025-05-30, 21:30:

quick update, interestingly, I found the sales flyer that came with the PC in which the motherboard was in and it says, turbo function is available using the keyboard to switch between 6 and 10mhz.

Anyone heard of this before and what would be the key combination to switch the modes?

How about getting a clear pic of the oscillator(s) currently on the board before flying off on all kinds of hypotheticals?

If the board can run at 10MHz as-is it will have some means of deriving that clock, either through a 20MHz oscillator or through circuitry that can modify the output of the current (12MHz?) one.

What circuitry that is will probably give a strong hint how to get the other speed, if possible. Right now we have no documentation and no clear pics of your specific board so at best can guess. It would be easier for all concerned if we could base those guesses on more concrete info.

Thanks for the reply and fair comment , I need to take it all apart and give it a proper clean as its very filthy with dust but thats a job for another day.

Here is a photo of the oscilators, its probably the best I can do for now, not sure if that helps.

https://i.postimg.cc/37jrwFYd/IMG-2545.jpg

btw I tried the CTRL+ALT+NUM +/- and when I press the combo, the + gives me two beeps, - gives one beep. But , running sysinfo it still show same processor speed , 6Mhz and same goes for the benchmark, when changing the turbo mode, the result slightly fluctuates but does not double / go up.

One oscillator shows 20MHz, the other looks to be a 12MHz.
The retroweb photos has 20MHz and 16MHz.

It looks the 12MHz is the one responsible for CPU clock. This lines up with "FSB speeds" reported as 6/8/10MHz on retroweb, so it should be ok to test the 12/16/20MHz oscillators in place of that 12MHz.

great thanks, I have the 12mhz cpu and 24Mhz oscilators on the way. I will get one 20Mhz oscilator as well and replace the 12Mhz one to start with and see what happens. 10Mhz should be sufficient for this machine but if I get a chance might play around with the other CPU and oscilators.

thanks again, I'll provide an update once I get a chance to make the changes.

vstrakh wrote on 2025-05-29, 11:00:

Because many things on the motherboard are working synchronously to CPU. It was not uncommon back in the day to have many onboar […]
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Omarkoman wrote on 2025-05-29, 10:47:

Sorry why not?

I would like to get 32mhz oscilators so i can use 16mhz 286 chip.

Because many things on the motherboard are working synchronously to CPU.
It was not uncommon back in the day to have many onboard clock signals derived from single oscillator by simple dividing.
. You can find yourself a 25 MHz CPU, but you're not replacing the rest of the discrete ICs.

Accurate,
there were upgrades mainly targeting the IBM AT 5170 that gave you a dial to overclock to any strange speed you wanted.

The thing is that you will find yourself likely needing to replace
1. To faster cpu
2. To faster more modern dram
3. Potentially needing to replace / upgrade disk drive controllers and video cards

I had a 10mhz 286, it was a more modern build but lacked a speed “rated” chipset .
I found with the original cpu or even with a more modern faster cpu it wouldn’t post past an even 15mhz, rock solid at 15mhz at that.

I attempted to replace the 100ns memory with 60ns and even then all it gained me was the ability to post at 16mhz but still unstable, replaced the onboard vram with faster chips and then it was stable and would post at 16mhz but even 18mhz would not post.

The variable cpu speed dinguses are getting rarer but I think 🤔 Ts possible to build one