Aleph-1 PC podule CPU upgrade

[Boydie]

From what I can gather from the reviews and publicity at the time, the first release of the Aleph-1 PC podule went through a few improvements over the space of a few months.
It was initially released as a 20MHz 386SX (this is what I have), but this was soon changed to either a 25MHz 386SX or a 25MHz 486SLC. Allegedly these were identical apart from which CPU was fitted. Also, the BIOS was loaded to the Arc's RAM rather than beng part of the PC card so presumably the BIOS updates to take advantage of the internal cache etc of the new CPU were provided via a new version of !PC.

So... I'm theorising that it should be possible to put my big boy pants on and remove the (surface mount) 386SX and replace it with a 486SLC. Can anyone see a reason why this wouldn't work (apart from my desoldering/soldering abilities)?

Or at least change the crystal and clock the 386SX at 25MHz instead of the stock 20?

Has anyone tried either of these before?

[SarahWalker]

I was unaware there was a 20 MHz version. I see no reason why swapping the crystal for 25 MHz wouldn't work.

In principle the 486SLC upgrade should work. However there were often minor motherboard changes required when upgrading 386SX PCs to 486SLC (around cache coherency) and I'm not sure if anything similar is required on the podule.

[Boydie]

Thanks. The only reason why swapping the crystal may not work is that it’s a 20MHz part, so a 25% overclock may be asking a bit much. Certainly clocking a 25Mhz part up to 33 (ie 33% increase) was pushing it BITD. Since it’s a decade or two before I started overclocking (except my StrongARM) I was wondering if anyone had any real-life experience on an x86 of that vintage - closest I’ve come is upgrading the CPU on a SunPCi card!

Edit: Reading around the subject, it would seem the motherboard changes were typically to tell the BIOS whaich CPU was fitted, so it could use the cache?
The equivalent on the Aleph-1 card is to change which CPU is fitted in !PC’s config. Since the BIOS is held in the Arc’s RAM, a Beebug review at the time claimed this was the sole difference between 386 and 486.