I have the same PS/1
I added an Intel overdrive CPU but I should have added this one. It will actually turn your 25mhz computer into a 66mhz computer.
See it has an extra pin in the center for a total of 168 pins.
https://www.ebay.com/itm/Intel-Overdrive-CPU- … 4f1edf93254c805

Hi,

i watched a few vids on youtube and one user was talking about that extra pin that would disable the onboard cpu and switched 486dx2 66mhz witch gives me more option when playing game on it for sure.

thx for the quick reply!

Just be careful. That overdrive cpu is 3v. I think the "487SX" was 5v.

Caluser2000 wrote:

Just be careful. That overdrive cpu is 3v. I think the "487SX" was 5v.

not quite sure,but this is the video i watched.

dx20dp66
l5200714
sz933

https://youtu.be/Eodr8IEIsmk?t=150

The video shows that the second cpu working so certainly worth a shot. From memory there was a 25mhz-33mhz jumper on these systems. I think there was a layout diagram on the top of the psu or underside of the top case.

Here's the PS/1 series service manual

kkcloak wrote:

not quite sure,but this is the video i watched. […]
Show full quote

Caluser2000 wrote:

Just be careful. That overdrive cpu is 3v. I think the "487SX" was 5v.

not quite sure,but this is the video i watched.

dx20dp66
l5200714
sz933

https://youtu.be/Eodr8IEIsmk?t=150

Yeah, The one I recommend is a 5v. that actually runs at 66mhz.
http://www.cpu-world.com/CPUs/80486u/Intel-ODP486DX-33.html

Your chosen CPU is a 3v or maybe 5v ?
Not sure but it runs at 66mhz too.
http://www.cpu-world.com/sspec/SZ/SZ933.html
http://www.cpu-world.com/sspec/SZ/SZ903.html

just make sure you get the one with 168 pins and make sure you align the pins correctly when installation.
It's really tight and hard to press in the socket. Easy to bend the pins as I did. I had to remove and straighten the bent pins and reinstall.

Caluser2000 wrote:

I think there was a layout diagram on the top of the psu or underside of the top case.

didn't find anything inside the case, only label i found was on the power supply.

thanks for the manual.

Intel486dx33 wrote:

just make sure you get the one with 168 pins and make sure you align the pins correctly when installation.
It's really tight and hard to press in the socket. Easy to bend the pins as I did. I had to remove and straighten the bent pins and reinstall.

so i installed the one i ordered from ebay, in the bios it now says :math coprocessor - installed.

but in the bios it still uses the stock cpu @ 25 mhz, and in windows when i check "system fitness"still list cpu has 486sx.

i think someone mentioned a jumper (only saw external battery, and external speaker).

will check the manual.

^ you got the ODP version right? because from your pic you want a 169pin overdrive not 168pins as mentioned above

ummm after looking at the manual and seeing this, i rewatch the video and noticed his ram was 72pin and mine are 30 pin.

so is possible this model cannot be upgrade to a 486dx2@66mhz?

keropi wrote:

^ you got the ODP version right? because from your pic you want a 169pin overdrive not 168pins as mentioned above

i got the one with extra pin to disabled the onboard cpu.

edit: this one here https://www.ebay.com/itm/Intel-486-OVERDRIVE- … 353.m2749.l2649

looking at the manual i found these jumper to switch cpu's but my board is level 1 not level 2 so jumpers are not there.

ok it's the correct one
did you try a benchmark?
I can't add anything more to this tbh as I never messed with those 487 sockets before... I plan to upgrade an IBM system with one though once I receive it: 487SX 169pin socket: any way to use a normal 486DX2 there?

keropi wrote:

ok it's the correct one
did you try a benchmark?
I can't add anything more to this tbh as I never messed with those 487 sockets before... I plan to upgrade an IBM system with one though once I receive it: 487SX 169pin socket: any way to use a normal 486DX2 there?

i'm pretty sure this system is not compatible, i decided to order another cpu but this time a 487sx to see if that works. (the socket on my board says it should).

I see... well I hope this one works but the overdrive u bought should be fine...

keropi wrote:

I see... well I hope this one works but the overdrive u bought should be fine...

its detected in the bios so i'm sure its fine.

got you pm will let you know.

I've posted it else where here. https://ps1stuff.wordpress.com/download/downl … -for-type-2133/ It's a great PS/1 resource site.

kkcloak wrote:

not quite sure,but this is the video i watched. […]
Show full quote

Caluser2000 wrote:

Just be careful. That overdrive cpu is 3v. I think the "487SX" was 5v.

not quite sure,but this is the video i watched.

dx20dp66
l5200714
sz933

https://youtu.be/Eodr8IEIsmk?t=150

If the bus speed is locked at 25mhz.
It should at least run at 2 x 25mhz = 50mhz. with your current jumper settings.
If there is a jumper to switch between 25mhz and 33mhz than you can remove that jumper and it should run at 33mhz.
originally, my PS/1 label read it was only upgradable to a 486dx2-50 overdrive with jumpers set at 2 x 25mhz = 50mhz.
I was able to upgrade my PS/1 to a 486dx4-100 Overdrive with jumpers set to 3 x 33.3mhz -100mhz.
My PS/1 did have a 486dx2-50mhz CPU before I upgraded it.
The bios only reads 486dx2 CPU installed even after the 486dx4 upgrade.
Your 66mhz Intel overdrive CPU should at least be running at 2 x 25mhz = 50mhz.

Down load this cdrom image.
extract and burn to cd.

It has benchmark tools. just run from you PS/1 cdrom
run "CHKCPU" to check CPU speed and "speedsys" to check everything.
https://www.philscomputerlab.com/dos-benchmark-pack.html

kkcloak wrote:

ummm after looking at the manual and seeing this, i rewatch the video and noticed his ram was 72pin and mine are 30 pin.

so is possible this model cannot be upgrade to a 486dx2@66mhz?

Should work with 4mb of 30-pin FPM -60ns ram.