Intel486dx33 wrote on 2021-05-05, 20:12:

What model # does the back label of your IBM PS/1 read ? Something like 5155 […]
Show full quote

BLockOUT wrote on 2021-05-05, 19:27:

Intel486dx33 wrote on 2021-05-05, 19:23:

I have several IBM Ps/1 and have upgrade them to the Max with CPU’s and Cache and RAM. […]
Show full quote

I have several IBM Ps/1 and have upgrade them to the Max with CPU’s and Cache and RAM.

I will say that save your MONEY.
For best value performance just change the jumper to 33mhz bus and install a 486dx-66 in Overdrive socket.
Add 256mb of cache.
The Intel Overdrive 486dx4-100 will only get you about a 10% performance boost over the 486dx2-66

Either way the game play performance is not going to change so don’t bother with it.
There is better game play performance in going from a 486dx-50 to a 486dx-66

So I would max out with the 486dx-66 and 256mb of cache if you can.

But if you are looking for best DOS game play performance then get a Pentium 100 thru Pentium MMX 233.
I like the Pentium MMX 233.
The Pentium MMX 233 runs like Cadillac and plays most DOS games and apps flawlessly in good performance.
Use a BX440 motherboard and 32mb of EDO ram.

That IBM PS/1 is just a collectors item. Not really great at playing DOS games.
Just restore it with what ever hardware will work and leave it at that.
But definitely install the original image software which you can find online.

What jumper? thats what we are trying to find , it doesn´t have 33mhz jumper.

What model # does the back label of your IBM PS/1 read ?
Something like 5155

Okay, I see from the photos that this motherboard is capable of accepting the Intel 486dx2-66 CPU
And 256kb of cache.
And 16mb of ram

That is what you will needed to get the best value performance out of this computer.
So not to spend too much money on it that really will not improve game performance.

Just change the jumper to 33mhz.

for the past 10 post we have been talking about that there is no 33mhz jumper on this motherboard

dionb wrote on 2021-05-05, 19:53:

Er, that's pretty par for the course for his posts... but it has set me thinking. That J37 is in the general vicinity of R251 and the PLL. According to the documents that's for the "Turbo switch". Interesting as I'm not sure that case has one, and even if it did, there's a jumper on J37 now, not a lead to a switch. Also it's in a block with J35 and J36, which sort of sounds like FS2, FS1, FS0 to me.

What happens if you remove that jumper cap from J37?

so we have J35, j36 and j37

- with and without the jumper on j37 its the same thing, i get no continuity between pin20 and ground.
- j36 = both of the contacts have continuity to pin20, not sure whats the purpose of it, since they don´t have continuity to ground.
-j35 = top contact has no continuity to ground, and no continuity to pin20, bottom contact has continuity to pin20 but no continuity to ground.

dead end, only old grandpa from UK that worked for IBM in the 90s should know what they did on this board and how they configured it to 66mhz
regarding soldering a jumper from pin20 to ground....i don´t know, who knows what else they did on the board and i can´t see the traces because of the mask they used to cover it.

to be honest i think there were different designs of this board for different PS/1 2168. it would be nice to see someone with the same motherboard set at 66mhz from factory. There is no IBM PS/1 collectors forum i belive.

If you remove the HD cable (can’t corrupt anything)

You could physically remove/place each jumper one at a time and fire up the machine to test what happens

That is what I do
the risk should be low and I’m guessing your machine can be jumpered to 33mhz regardless of it listing the setting

On post if one of the jumpers nets you 33mhz your good to go