User Anonymous Coward has probably mastered this topic. PM him if he does not chime in.

In my experience, proprietary 386SX upgrade modules will usually work on standard 286 boards IF you can get them to fit in the CPU sockets without obstructing the ISA slots or something else. Some of them can be quite bulky. I have run two Buffalo 286 to 486DLC adapters in my original 5170 AT motherboard. They were designed for Japanese PC98 systems, but they seem to work fine.

Whatever you do, make sure your upgrade has some cache (they usually do), as that seems to have a bigger overall affect on performance than a very fast CPU.

thanks for the info Anonymous Coward - it goes without saying that cache is the most important thing on these upgrades , I had a 486slc2 upgrade for a 386sx cpu once, it was the measly 1kb of cache that provided the speed boost.
I have looked at the kingston upgrades - sadly they conflict with the ram slots on my mobo:

I will have to check if the PLCC socket is smd or hole-thru. If it's thru-hole I can elevate it or something... 😁 we'll see

I'll look again at the ones I have. I should be able to determine if at least one has the POSSIBILITY of fitting.

Without modification, the small modules based on the TI486SXLC2 are probably your best bet. I think Evergreen made one, and possibly there was a version from Improve It Technologies (Make it 486), which seems to be pretty rare.

I will have to take apart the machine and see what kind of PLCC socket it has. If it's hole-thru it's easy to elevate it, I will update with some pics in next couple of days.
Thanks for the interest/help mates 😀

@keropi

took some pics for you (and others) http://imgur.com/a/M5YzG

The best candidate I have is the large upgrade from kingston. SX/33LFM

but it might be too big. It is 80mm x 105mm. The cpu is located ~15mm from the edge (top of the picture) and ~22mm from the left edge and is 25mm square. You will need ~55mm between the cpu socket and the isa header, in that picture you posted.

I also posed a picture of the damage I described. The board is ok, but the connector needs to be heat-gunned off, and repaired/replaced. There are other with bent pins and missing caps, but those are also easy fixes.

Interesting photos, I will make some measurements but I think something like that will fit... actually I will make a paper cutout and see if it fits 😀

Thanks for the info luckybob, appreciated!

Using advanced 3d printing technology I determined there is space of an upgrade like the SX/33LFM provided two things happen:
a. I raise the cpu plcc socket so the board goes above the ram
b. I notch some unused pcb in the isa riser bottom right corner

Both are no problems and I have verified the motherboard's plcc socket is indeed a hole-thru one.
So there is hope after all 😁

Cool! :) I never had one of them. May I ask if there are any floppies included/required ?
As far as I know, older 286 BIOSes didn't emulate LOADALL yet because it was actually supported by the 286.

"hacked" one of the kingston upgrades to a test 286 mobo:

It's working well, if cache is not enabled SysInfo gives a score of 6.2
Because it has those 16kb of cache the speed boost is real, wolf3d is way better, jazz jackrabbit almost has perfect scrolling, alone in the dark is snappy 😀
I will transplant it to my main 286 setup soon.

YAY!

My 286 has 8MHz and no oscillator onboard. Its only switchable to 6mhz directly in the bios settings.
Would an 386 or 486 upgrade increase something like doubling the clock for example?

Even with an 8MHz bus, you should still see a pretty substantial improvement with a 386 or 486 CPU upgrade provided that it has some cache.
Almost all of the upgrades have clock doubling. I have upgrades that allow for higher multipliers (up to 8x), but I'm not totally convinced there is much of a real world speed boost.
I still recommend TI 486SXL(C) as an upgrade product (8kb internal cache). The IBM SLC2 upgrades can be a lot harder to get working properly, especially if you have exotic hardware installed.

I wouldn't personally touch 386sxs at all. For 16-bit operations they need to do twice the work. A 386SX20 is about the same as a 286/10 in that regard.

*286/16

Jo22 wrote on 2021-07-08, 01:14:

*286/16

Your keyboard appears to be broken dude...😉

The bigger question would be how and where I can get such an upgrade. It seems impossible right now to find something like that or has someone left for me?

Caluser2000 wrote on 2021-07-08, 00:57:

I wouldn't personally touch 386s at all. For 16-bit operations they need to do twice the work. A 386SX20 is about the same as a 286/10 in that regard.

CPU Galaxy made a video about the 286 -> 386 upgrades. At the same clock speed, the 386 is slower when no cache is involved. If the upgrade board comes with cache then you will see a significant performance boost - especially since these higher end upgrade boards with cache come with 25 or 33MHz processors.

Personally I'd be more happy running a 25MHz 286 (I already have a decent 386 build based on a VLB motherboard and a TI 486DLC chip) but none of my boards will run stable at that clock speed. Best I could do is 20MHz using a 25MHz Harris CPU and a 40MHz oscillator.