See my posts:
IBM PS/1 Multimedia ( max restore ).

Search this manual for your motherboard type as there were many PS/1 models.
http://ps-2.kev009.com/pccbbs/aptiva/63g2028.pdf

You can solder on low value ohm resistor to one of the solder pin for the 487SX upgrade socket to disable the 486SX CPU so you can use normal DX 33 or DX2 66 in that socket.

487SX 169pin socket: any way to use a normal 486DX2 there?

Cheers,

Thanks guys,

I did some more reading and it seems the safe choice is to make the resistor mod and buy a 486DX2-50.
Did I get this right?

However it would be awesome if we could find some info about the 'micro select'-jumpers 23, 24, 25 to change the speed to 33Mhz.
Maybe it's possible to get this sucker up to 100Mhz with a Voltage regulator board and the 486DX4-100?

All suggestions welcome!

Here are the motherboard jumper setting and compatible CPU’s
For a 486dx-33, 66, or 100 you need to change the bus speed for 33mhz CPU.

Otherwise you can use a 486dx-50 0r 75.

More docs.
I don’t know if you just pop in a standard 168-pin CPU in the overdrive socket if it will work.
Other wise you will need an Intel Overdrive 169-pin CPU. ( 486 overdrive or Pentium overdrive for 486 ).

Here is a write-up I did on the IBM PS/1 that has a motherboard similar to yours.
Re: IBM PS/1 Consultant MultiMedia edition.

I had to change the jumper settings and use the Intel Overdrive 169-pin CPU.
There are several Intel Overdrive CPU’s that will work.

So basically, you want a balanced system.
You don’t want to invest allot of time and money into it if it is not going to run at optimal performance.
So if you plan on using a 83mhz Pentium overdrive you want to use a CF card.

You want 8mb of ram at least but 16mb should be max and best for DOS/Win3x
32mb for Win95

A 486dx2-33 is a little slow for Quality DOS game play.
A 486dx2-50 is okay but A 486dx2-66 is best. The 486dx2-66 has features that improved performance over the 50mhz variant.
I don’t recall what it was but the 66mhz CPU performs about 25 percent better than the 50mhz variant.

So there are several 486 Intel Overdrive CPU’s
You will need the one with the extra pin ( 169-pins ).
Some are labeled Intel Overdrive 486-33mhz and 486-66mhz but they are both the same I think.
At least they both run at 66mhz. It was just a marketing confusion on what to label the CPU as.
You can check with www.cpuworld.com to confirm speed and voltage.
They all will work in a 5v socket.

If you just want a good DOS/Win3x computer then this is the best setup.
486dx2-66 overdrive CPU
16mb ram
256kb cache.
Most video ram.
Standard IBM hard drive ( 170mb )

I am not sure which Pentium overdrive CPU works.
But for modern DOS game play and Win95 the Pentium overdrive is bests.

Overdrive is hard to find and expensive, Get 486dx2 66 and do a mod on the motherboard's solder side cpu socket to disable the 486SX.

Cheers,

And the Multimedia edition of the PS/1 came with a Sound Blaster 16 with Yamaha OPL3 and a Panasonic 2x CDROM drive.

Thanks guys,
When I went through that service manual the other day I didn't find my board. But now that I had a closer look at the attached image its actually very similar to my board. There are just a few differences so it's more than likely that J23-J25 is the same.
In that case I think I could change J25 to get my 33Mhz and together with the resistor bodge I can use 486DX2-66 or DX4ODPR100 😀

I have ordered a DX2-50(late model with SL) just so I can get the project of the ground But I will keep hunting for the DX4ODPR100/DX4ODP100 or a voltage regulator board for the DX4-100.
If I can find the schematic for the regulator board I'll try to make one.

I have ordered 8+8 MB ram so I can remove one SIMM if I get any compatibility issues with the oldest games.

I got some great help with the sound card in a separate thread. I ordered a card with an extra CDROM IDE because the board only has one IDE channel.
The PS/1 came complete with the original hdd. Let's see how far I can get with 85MB haha. My first IBM back in the day only had 20MB 😀

I guess my last problem is to find the correct cache. I'll get back to my reading...

I guess my last problem is to find the correct cache. I'll get back to my reading

These should work, just get 9 pieces. One for the tag.
https://www.ebay.com/sch/i.html?_from=R40&_tr … HE+486&_sacat=0

Intel486dx33 wrote on 2020-04-23, 20:23:

I guess my last problem is to find the correct cache. I'll get back to my reading

These should work, just get 9 pieces. One for the tag.
https://www.ebay.com/sch/i.html?_from=R40&_tr … HE+486&_sacat=0

Thanks bro, they are on their way. 10pcs 32K × 8, 20 ns SRAM

I had to guess that 20ns would work both for cache and tag. hope I didn't mess it up 😀

epictronics wrote on 2020-04-24, 21:29:

Intel486dx33 wrote on 2020-04-23, 20:23:

I guess my last problem is to find the correct cache. I'll get back to my reading

These should work, just get 9 pieces. One for the tag.
https://www.ebay.com/sch/i.html?_from=R40&_tr … HE+486&_sacat=0

Thanks bro, they are on their way. 10pcs 32K × 8, 20 ns SRAM

I had to guess that 20ns would work both for cache and tag. hope I didn't mess it up 😀

yeah, that's what I have in my PS/1
256kb is max.
And is enough for a 486. Not much more gain with 512kb.