It's not quite a real 486. The socket will not be compatible with standard 486 chips.
There are socket adapters that do what you want, but this isn't one of them. I have one (Transcomputer 486HPi) that does indeed let you use 5x86 chips on a 386 board.

Anonymous Coward wrote:

It's not quite a real 486. The socket will not be compatible with standard 486 chips.
There are socket adapters that do what you want, but this isn't one of them. I have one (Transcomputer 486HPi) that does indeed let you use 5x86 chips on a 386 board.

Ah, ok, well it's good to have on hand anyway... what about this one? I also have one of these. Will this work as it has a real 486 (though it is an SX)

http://ohlandl.ipv7.net/CPU/Kingston_486-Now.html

Got some time to plug it in to my compaq 386 and run a few benchmarks. Anyone any idea if the 486 can be replaced using this board?

What's under that Kingston sticker?
It's irritating that one benchmark tells you it's an 486DX, but there's clearly an SX on the PCB.
Maybe there's a DX soldered next to it?

The problem here is that your CPU is 5V. To get, f.e. an DX4 running, you'll need a 3.3V regulator board inbetween.
After that - theoretically - you shall also be able to run a 5x86 and other fast CPUs!

Very nice adapter you've got there 😀

Indeed. I wonder what that big IC with the kingston label really is!
The GALs shall be readable in theory and a clone of this board would be awesome

I am pretty sure the answer is yes. A 5x86 should work in that Kingston upgrade provided you have a VRM.

Thanks for the responses guys. My soldering / desoldering skills are decent, but I don't really want to have to unsolder 168 pins.

Does anyone know of a trustworthy & professional soldering / desoldering service? I'm planning to add a PGA168 socket onto the board so I can test out different PGA168 CPUs.

The 486 is already socketed. Just lift it carefully

Really?? I don’t think so. There isn’t a socket, the pins from the cpu do extend into the pcb, as you can see in the pics. I think the tips of the pins are soldered to the silver “pin holder” on the other side if that makes sense

To me it also looks like it's socketed. Not in the usual way. But try lift it up a bit on one side.

It is socketed, trust me! The "pins"are so wide underside because of the springs inside

Yeah, looks like "tulip" sockets, like the pins in these: https://www.google.com/url?sa=i&source=images … 554297438945669

You guys are right. I got a knife under there and gently pried it off! Now to get an AMD5x86 upgrade! Thanks guys!!

Remember that this socket gives your CPU 5V! For 3.3V CPUs, you need an adapter with built in regulator!
When your 5x86 is compatible with 5V (e.g. contains regulator), everything is fine.

LeFlash wrote:

Remember that this socket gives your CPU 5V! For 3.3V CPUs, you need an adapter with built in regulator!
When your 5x86 is compatible with 5V (e.g. contains regulator), everything is fine.

No worries. I sprung for an upgrade kit with the voltage regulator. It’s going to be interesting to see how fast I can get my compaq 386! 😎

Ok so I replaced the 486sx with a 486dx2 and I couldn’t get the compaq to POST, just ram check then blinking cursor but then nothing. The 5x86 with the 5v to 3v adapter was worse, the screen didn’t even turn on when I flicked the power switch.

Anyone have any suggestions on what might be compatable with this Kingston board (and perhaps also with my compaq 386?) it’s one of the first 386’s so I’m not sure if that has anything to do with it, or is it just the Kingston board not playing nice.

Any suggestions? Maybe I could go the route of overclocking the 486sx, but I’d like to try other means before playing with replacing the 33.333 Crystal. Do you guys think a Pentium overdrive would work as they are advertised and replacements for a 486sx on the box. Maybe something from cyrix or AMD? What were the most compatable upgrade options for a 486sx?

Do you have an 486dx (33 or 40mhz) for testing?
I can only imagine that there's a problem with the built-in FPU in the DX or later processors.

I doubt that’s the problem as if you read here this Kingston “486 Now” came in dx and sx flavours and I bet the board would be the same for both, and they swapped out the processors. http://ps-2.kev009.com/ohlandl/CPU/Kingston_486Now.pdf