Kingston 386 to 486 CPU Upgrade Board

[Vintagehk]

Hi guys, this is my first post here. I’ve posted about this issue I’ve been having on Vogons, but I also wanted to share it here as well as its directly related to Vintage CPUs.

I recently acquired a Kingston 486 Now 386 to 486 CPU Upgrade Module (pictured below) that’s designed for an IBM P70, but from what I can tell, this range (486 Now) was made for IBMs, Compaqs etc (See original Kingston website here) and it came in SX and DX varieties. The board that I got was an SX version.

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The computer I’m using it in is a Compaq Portable 386, a very early 386 so there are no BIOS settings etc that you can set.

Plugging it in with an original SX, I get the computer to boot and everything is fine, but I had bought this upgrade with the hopes of upgrading the CPU, and a 486SX 33 is not exactly fast – in fact I have a drop in PGA 132 TI486 SXL that is so far, much faster than the upgrade board.

The first CPU I tried was a DX, and the computer did it’s ram count on boot then hanged. All DX processors had the same result.

I tried a SX2 and this booted, however it seems like the clock-doubling is not having any effect on processor performance. Also the cache on the SX2 seems to be not working correctly (maybe being flushed too often?)

Here’s the computer with the SX:




Here’s the computer with the SX2:
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I also plan to swap out the crystal on the board to overclock it to see how far I can get it to go, but ideally, I would like to get the SX2 working as it should first.

Anyone have any ideas on why the clock doubling is not having an effect? Is it something to do with the pinout on the Kingston Board and the SX2?

(I thought the SX2 was a drop in upgrade to the SX, and it’s supposed to work in any SX slot?)

Then there’s the other route – is there an easy way to get a DX to work, or is the limitation on the board so great that I shouldn’t bother?

Looking forward to your feedback, or any thoughts or tips! thanks guys!!

[Guest]

Very cool! Super jealous of that CPU board... my P70 still awaits one if I ever see one for sale! Crazy how prevalent these things used to be and how hard they are to locate now.