Maybe you'll need to change the clock crystal, is it socketed?

Edit: Had a look at the pictures, the crystal is clearly a 50MHz one and it's socketed.

I found out its indeed running at 25 fsb. I don't know about the fsb crystals. Does that mean I have a 50 crystal so it runs at 50 or 25? So if I want 33 fsb what crystal would I need?

This is from the manual

CPU SPEED CONFIGURATION

Type

JP12

20MHz

pins 2 & 3 closed

25MHz

pins 2 & 3 closed

33MHz

pins 2 & 3 closed

50MHz

pins 1 & 2 closed

You need 66MHz one.

Can you run Speedsys and post screenshot? I'm wondering about L2 cache on the motherboard.

Kamerat wrote:

Maybe you'll need to change the clock crystal, is it socketed?

Edit: Had a look at the pictures, the crystal is clearly a 50MHz one and it's socketed.

I agree with this.
Jumper JP12 makes provision to either run at full speed of the clock crystal or by a divider of 2 (in this case, either 50 MHz or 25 MHz).
If you do swop out the crystal for a 66 MHz one, then I would not recommend you try to set JP12 in the 1-2 position, as you would then be running your FSB at 66 MHz.

Ok great thanks for explaining it to me, I will look around for a 66mhz crystal
Here is some screens of cache info, sorry not the best quality pic

Yes I will definitely keep it at half rate not interested to see what happens at 50 or 66mhz

I don't know anything about this board, but based on what's been said, it might be more useful to get a 33MHz crystal. That way you'll have a usable slowdown option.

kixs wrote:

Can you run Speedsys and post screenshot? I'm wondering about L2 cache on the motherboard.

L2 cache looks fine.

This is the first time im learning about crystals so it's all new to me, but if there is a 33mhz one I think that makes more sense to me too since I will never need or want to use 66mhz, unless there is more to it.

The only overclocking I did was on Slot1 and socket 370 in the past which were all bios controlled

You need 66MHz crystal as the frequency is divided by 2. At the moment you have 50MHz one and you get 25MHz bus. With 66MHz one you'll get 33MHz bus. Your DX4 needs 33MHz bus to run at 100MHz.

If you mean bus the fsb the cpu runs it came initially with 50mhz and a 486dx50 cpu which I believe runs at 1x50mhz but I changed the pin and now its running at half fsb 25 so 3x25 but for my dx I want the 3x33=100

However this also gets me thiking what about the isa and ram? If I get a 66mhz crystal and run it at half speed or a 33mhz crstal and run it at full speed will it the same system wide? Because like mentioned before a 33mhz crystal running at full speed can still be set to half through jumpers, probably not useful at the moment, however a 66mhz chip running at half will never be useful to me running at full speed of 66mhz

This is my reasoning and logic after 5 minutes of learning about crystal oscillator

Edit: ok so looking for the part they don't seem to be too popular so I think ill settle on 33 or 66 whatever is easier to find as long as they will both work the same with half clock and full clock respectively. Mine is a koyo kco-110s
Do you guys know if can replace with another brand or better stick to same one?

The oscillator will always generate the same frequency. I believe that the motherboard has a jumper (25/33 or 50) which will either halve it, or use it at full speed. This is used to set the bus speed. As an example, with the jumper in 25/33, the 50MHz oscillator signal is halved, giving you a 25MHz bus (50MHz/2). The Intel overdrive, despite the "DX4" name, has a 3x multiplier. Therefore, it operates at 3 times the bus speed. In this case, 25MHz x 3 = 75MHz. It seems that the only way to alter the bus speed up to 33MHz is to replace the crystal oscillator with one double that of your desired bus speed.

Ok, thanks for the more details.

So on my board I have a jumper setting for 50mhz or 33/25
So then best to get a 66mhz crystal and set the jumper in the 33/25 position?

Can I use this one?
https://au.rs-online.com/mobile/p/crystal-osc … lators/4785941/

I think that I gave you slightly incorrect information. I shall amend my post above, but re-iterate here.

I think that the 25MHz/33MHz or 50MHz jumper could actually be what cuts the oscillator in half. 50MHz bus speed does exist.

Nevertheless,

So then best to get a 66mhz crystal and set the jumper in the 33/25 position?

Should still be correct.

I expect that this made it easier to use the same motherboard with SX-25, SX2-50, DX-25, DX2-50, and DX-50 all with the same oscillator crystal.

What you're looking for is a DIP-14 66.000 MHz oscillator. I don't think that the one you've linked is compatible. If you have any desire to run at a 40MHz bus, then you'd want an 80MHz crystal.

https://www.ebay.com/itm/401181050200 is what you're looking for.

Great thank you for the explanation and solution for me!
I will order the part you linked, 80mhz is also tempting which would give me 3x40 =120mhz, something to think about in the future for now I will first get it going at 100mhz
Will take a week or 2 since im in Australia but Ill make a update when I get the oscillator

treeman wrote:

If you mean bus the fsb the cpu runs it came initially with 50mhz and a 486dx50 cpu which I believe runs at 1x50mhz

That is correct. There are two variations of 486 that run at 50 MHz. The first ones were regular DX50 CPUs, with the bus at 50 MHz. As it proved troublesome to run the entire bus and chipset at 50 MHz, Intel later introduced the DX2-concept, which launched the DX2-50, running at 25 MHz FSB, and the more familiar DX2-66, running at 33 MHz FSB.
So if you have a DX50, it will indeed run at 1x50 (or 1x25 if you set the jumpers to halve the clockspeed).

Ok the crystal that fitzpatr linked came, I fitted it and running at 99mhz so mission success.

In the meantime I also localized a Kingston turbo chip 586 133 which is a 586 in a 3v to 5v convertor. Which is supposed to run 4 x 33.

So Kingston went in next but looks like 116mhz is the fastest this board will go, I read this before on a different thread.

Also I think only 100mhz is being used because 116mhz
586 Kingston turbo chip got exactly the same score as intel overdrive at 99mhz

So quiet happy with this result pushing the max from a 486 isa system is what I wanted, thanx for all the contributions

It sounds like the Kingston turbochip may be operating in 3X mode. You might need to change a jumper in order to get it to run in 4X mode.

As far as I know, the Kingston Turbochip won't really be any faster than the IntelDX4 even at 133MHz, due to the DX4's superior design (only applies to intel dx4s). However, if you get the 80MHz oscillator, there is a good chance that the turbochip can overclock to 160MHz, which would be a worthwhile upgrade.

The TurboChip I own has a fixed 4x multiplicator - are there any variants with dip switches?
Mhz numbers shown in combination with the Cyrix string in SI are usually incorrect.