Hm, if you haven't changed the FSB (trying to run it at 150MHz) it shouldn't even POST.

Nothing automatic on a 486, need to jumper the correct FSB

These are the jumper settings I have available on the motherboard.

The computer is an IBM PS/1 that originally had a Intel 486dx-50 CPU.

I guess you mean dx2-50..?

It makes fully sense then. The DX4 runs at three times the FSB, so 3x 25 MHz = 75 MHz. You need to raise the FSB to 33 MHz.

Okay, I am going to try the overdrive CPU jumper settings.
I think all 486 Intel Overdrive CPU’s run on a 33.3 FSB right ?

IBM PS/1 Change FSB

When I played around with my PS/1 I noted no FSB setting
These systems came in sx25 and sx33 so

I believe you need to change the clock crystal

Intel486dx33 wrote:

Okay, I am going to try the overdrive CPU jumper settings.
I think all 486 Intel Overdrive CPU’s run on a 33.3 FSB right ?

No. The Overdrive 50 and 75 runs at 25MHz FSB.

rmay635703 wrote:

IBM PS/1 Change FSB […]
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IBM PS/1 Change FSB

When I played around with my PS/1 I noted no FSB setting
These systems came in sx25 and sx33 so

I believe you need to change the clock crystal

That’s the motherboard manual I have been looking for. Thanks.
I will give it a try.

Here's the datasheet for the clockgenerator on your board. You'll need to measure where the pins for FBS setting goes and then just change as needed.
I would start with J35, J36 and J37.
http://pdf.datasheetcatalog.com/datasheet/ics … 155C-01CW20.pdf

what you need to do is install some L2 cache on this montherboard

keropi wrote:

what you need to do is install some L2 cache on this montherboard

Yes have been putting that off because I did not know the jumper settings but thanks to all your posts
I now have the correct manual with jumper setting.
I just put in 265kb of cache an it works fine.
And 64mb. Of ram.

Do you think it is okay to use this Intel 486dx4-100 Overdrice CPU at 75mhz ?
This overdrive CPU has a built in voltage regulator right? So I don’t need to worry about over voltage.
I have the motherboard jumpers set for a 486dx2 is that okay ?
The circuitry on the overdrive CPU compensates for that right ?
Or do I need to set it up for a 486sx or 486dx ?

Currently it is running stable in benchmarking.

The motherboard in that PS/1 probably only has a 25MHz FSB. It's called a PS/1 or PS/Valuepoint for a reason 😈

The multiplier setting should be 3x, but it's possible that the Overdrive CPU overrules the motherboard's multiplier setting, if I remember correctly. Other than that leave everything stock.

SpectriaForce wrote:

The motherboard in that PS/1 probably only has a 25MHz FSB. It's called a PS/1 or PS/Valuepoint for a reason 😈

The multiplier setting should be 3x. Other than that leave everything stock.

Well, Supposably it supports a 486dx-33
So I don’t know why I can’t get it to work with this overdrive CPU @ 33.3mhz ?
And it has a good onboard video in the Cirrus logic CL-5428 with 1mb ram.

Intel486dx33 wrote:

Well, Supposably it supports a 486dx-33 So I don’t know why I can get it to work with this overdrive CPU @ 33.3mhz ? And it has […]
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SpectriaForce wrote:

The motherboard in that PS/1 probably only has a 25MHz FSB. It's called a PS/1 or PS/Valuepoint for a reason 😈

The multiplier setting should be 3x. Other than that leave everything stock.

Well, Supposably it supports a 486dx-33
So I don’t know why I can get it to work with this overdrive CPU @ 33.3mhz ?
And it has a good onboard video in the Cirrus logic CL-5428 with 1mb ram.

But where do you get that information from and is it about the exact same model? Many PS/1 variants exist. Even then you could still hit a brick wall because the BIOS might not support your DX4 Overdrive.

it is no issue for the 100mhz overdrive to work at 75mhz - and yes these are 5v cpus so no problems there!
last time I checked there are no jumpers on these mobos to select the FSB so your system runs at 3x25mhz instead of 3x33mhz
I have a similar PS/1 system that came with 486sx25 and supposedly it also comes with sx33 but the FSB setting is soldered to the main chipset so when I upgraded with a DX2 cpu I ended up with a DX2/50mhz ... I am not that interested in changing the hard-coded FSB value tbh... but it's doable if you track down your chipset's datasheet (posted the 82C480 one in my 487sx socket thread)

what do J12, J13, and J16 do?

bakemono wrote:

what do J12, J13, and J16 do?

Set the cache size,

As stated the FSB is hard wired which takes a rewire or a new crystal

Interesting thing to do would be to run a 5x86 at 25mhz x 4 , should be within 10% of a real dx4

Without a manual so, What do J51 and J24 do?
J51 looks clost to the cache but J24 is near the cpu seletion of J25 and J31.

I

Did some more research based on my guess of J35, J36 and J37 that are close to the frequencygenerator. Came up with this.

So it seems that J37 switches between 25 and 33MHz bus.