You will need to change the bus speed to be 33Mhz instead of 40Mhz. You don't have to replace the CPU at all.

Most likely you will need to change the clock crystal on the motherboard to change the speed.

You can also look to see if there is a header on the board for a "Turbo" button. If so, you could just hook that up and it should lower the bus speed.

Pictures of the motherboard would help.

Second cyclone3d's advice.
Some later 386 motherboards allowed you to change the bus speed via jumpers but, to swop out the oscillator is not that of a big deal (you should see it on your motherboard with an 80.000 or 80 MHz marked on it - or something similar).

Thanks for your answers , unfortunatly i do not have the jumper to change the bus speed on this motherboard.

this is not mine but mine is exactly the same :

http://minuszerodegrees.net/at_clone_bios/UM3 … ision%201.1.jpg

http://stason.org/TULARC/pc/motherboards/E/EL … 386-UM-386.html

with the dx 40, i tried to put a jumper on the turbo pin, in this case it runs at 20 mhz but it's a bit to slow.

when i install the dx 33, the cpu runs at 40mhz.

The little metallic can (zip tied to the motherboard) with the number 80.000 MHz written on its top needs to be replaced with one that says 66.xxx MHz. (~$2 at Ebay, $10 will likely buy you a whole bag)

The "oscillator" makes the rerference signal that decides the CPU speed. In this case the CPU will run at half of what ever speed the oscillator oscillates at.

Does it do that after you restart the computer? What you can do is remove the battery from the header for a few seconds and turn the system on and see what happens. My Packard Bell does the same thing when I put a faster CPU in there after changing the jumpers from 25MHz FSB to 33MHz FSB.

Replace the oscillator as suggested with a slower one (that says 66.000MHz) since the one that's on there might be the reason why it's reading as a 40MHz CPU instead of 33MHz. If there was a way, you can also put two oscillators on the motherboard with a switch to toggle between the 66MHz and 80MHz oscillators if you want to switch the CPUs back and forth (don't know if that'll be possible or not, but I digress).

If the BIOS gives you options to change wait states, which most probably does, increase them step by step and check with some utility the result until you reach the dx/33 level.

Skyscraper wrote:

The little metallic can (zip tied to the motherboard) with the number 80.000 MHz written on its top needs to be replaced with one that says 66.xxx MHz. (~$2 at Ebay, $10 will likely buy you a whole bag)

The "oscillator" makes the rerference signal that decides the CPU speed. In this case the CPU will run at half of what ever speed the oscillator oscillates at.

perfect, i'm going to get one. thank you

bjwil1991 wrote:

Does it do that after you restart the computer? What you can do is remove the battery from the header for a few seconds and turn the system on and see what happens. My Packard Bell does the same thing when I put a faster CPU in there after changing the jumpers from 25MHz FSB to 33MHz FSB.

Replace the oscillator as suggested with a slower one (that says 66.000MHz) since the one that's on there might be the reason why it's reading as a 40MHz CPU instead of 33MHz. If there was a way, you can also put two oscillators on the motherboard with a switch to toggle between the 66MHz and 80MHz oscillators if you want to switch the CPUs back and forth (don't know if that'll be possible or not, but I digress).

i tried but nothing change here. i am going to replace the oscillator.

I'd try already mentioned BIOS setting first. Set cache, memory timings, ISA bus to the slowest. Disable cache all together. If this isn't slow enough, there are programs for slowing the cpu. As changing the OSC is quite drastic approach and only worth it if this game is the only purpose of this computer.

kixs wrote:

I'd try already mentioned BIOS setting first. Set cache, memory timings, ISA bus to the slowest. Disable cache all together. If this isn't slow enough, there are programs for slowing the cpu. As changing the OSC is quite drastic approach and only worth it if this game is the only purpose of this computer.

Personally, I like to desolder the oscillator and solder down a socket in its place. Then you can easily switch them on the fly with little trouble. In a pinch a wide (300mil) DIP socket works well for this; just cut it apart between pin 4 and 5 (so you end up with an 8-pin socket) then clip pins 2, 3, 6 and 7. Voilà! You now have a socket the crystals will fit in.

Alternatively you can simply get single female headers and solder one down in each hole of the crystal’s footprint. If you go this route get good quality ones from Digi-Key, e14, Mouser, etc. (not eBay), as you want to make sure the inner contacts put good pressure on the pins of the crystal to hold it in place and prevent intermittent signal issues.

timb.us wrote:

kixs wrote:

I'd try already mentioned BIOS setting first. Set cache, memory timings, ISA bus to the slowest. Disable cache all together. If this isn't slow enough, there are programs for slowing the cpu. As changing the OSC is quite drastic approach and only worth it if this game is the only purpose of this computer.

Personally, I like to desolder the oscillator and solder down a socket in its place. Then you can easily switch them on the fly with little trouble. In a pinch a wide (300mil) DIP socket works well for this; just cut it apart between pin 4 and 5 (so you end up with an 8-pin socket) then clip pins 2, 3, 6 and 7. Voilà! You now have a socket the crystals will fit in.

Alternatively you can simply get single female headers and solder one down in each hole of the crystal’s footprint. If you go this route get good quality ones from Digi-Key, e14, Mouser, etc. (not eBay), as you want to make sure the inner contacts put good pressure on the pins of the crystal to hold it in place and prevent intermittent signal issues.

In this case the oscillator is already in a socket so replacing it is not something I would call a "quite drastic approach." 😀

I would get a 100 MHz oscillator as well to see if the AMD DX40 CPU and the motherboard will handle 50 MHz! 😁

Didn't see the photo before. If his is socketed then it's an easy fix 😀