To me, that photo shows pin 30 (FLUSH#) cut off to make room for the wire to be connected to pin 31 (A20M#). The other photos showed the opposite end of the wire connected to pin 22 on the 8042 which is the A20 gate, so it makes sense that it goes to A20M#.
The bodge wire exists because this is a 386 board not designed for a cpu with an internal cache/A20M# pin.

jmarsh wrote on 2020-09-26, 12:59:

To me, that photo shows pin 30 (FLUSH#) cut off to make room for the wire to be connected to pin 31 (A20M#). The other photos showed the opposite end of the wire connected to pin 22 on the 8042 which is the A20 gate, so it makes sense that it goes to A20M#.
The bodge wire exists because this is a 386 board not designed for a cpu with an internal cache/A20M# pin.

yep 100% correct
I just assumed that there would a trace we patch - somehow I missed it was it the next pin we are interested in...!

So I did not cut or lifted any pins - I just soldered on pin31 (will move it on the bottom of the pad since the upgrade was a success)

this is the newer 486slc-aware bios:

With this bios alt+ctrl+numpad(+) change the system's speed , benches are on "high"

I will post some mobo pics when I finalize the patch wire - I soldered it directly to the WDC chipset next to vga but now I am thinking to solder it on the kbc but on the top side , I don't like that patch wire going to bottom side (not to mention I have soldered the extra 4simm slots so no hole like amstrad did

Thansk to Dioxaz for sharing the info and files and Zalog for sending me a good cpu to test this!!!! 😀

keropi wrote on 2020-09-26, 14:50:

I will post some mobo pics when I finalize the patch wire.

Thansk to Dioxaz for sharing the info and files and Zalog for sending me a good cpu to test this!!!! 😀

Well Done 😃 and congratulations on getting it working 👍 - glad the MAB processor sorted things for you and got it running. It's fantastic to be able to prove another upgrade path for 386 board folk, and also solve another bit of MegaPC plus folklore in the process !

I can't wait to see your final patch wire solution, with your skills, its going to be a neater job than amstrad did! 😁.

well.... it's not a *huge* performance upgrade I am sure - but it's a "because we can" upgrade 🤣
atm I have the patch wire like this:

and I think I'll do it like this: pass it under the fpu socket and solder on the kbc pin from the top side - it's not like you mess with it anyways... I don't like wires looping at the back if they can be avoided

I think it will look ok in the end 😀

Allright I spent some time on this patch wire so here's my take on this

first of all this is the alternative point in case someone prefers to solder directly to the chipset:

This is the connection for the cpu pin#31 (amstrad's way is also ok since you get more room to make a nice solder connection)

Patch wire goes under the nearby resistor networks and under the kbc socket - with a couple of hotglue blobs to secure it

kbc connection like this

overal

hope the pics help someone in the future 😀

I have removed the benchmark screens from the initial post because I found out that 486slc needs to have ram filled by x4 ram sticks - x2 sticks will work but there is a speed penalty.
I was getting better results in Wolfenstein3D benchmarks with the 386sx cpu , 486slc performed 1fps slower 🤣
Then I noticed on cachechk that it reported :

• for 386sx: a RAM bank is 2 bytes wide
• for 486slc: a RAM bank is 4 bytes wide

I was testing the 486slc with 2x1MB ram sticks and switching to 4x1MB I got some better results:

• wolf3d from 13 to 14.4 fps
• sysinfo went from 29.9 to 33.8
• 3dbench went from 7.9 to 8.4
• landmark from 90.81 to 92.76

So... how does it compare to a 386sx system?
386sx -> 486slc
Sysinfo: 18.1 -> 33.8
Landmark: 34.15 -> 92.76
Wolf3d: 14.1 -> 14.4 fps
3Dbench: 7.8 -> 8.4

There is some small improvement but it's small as you can see in Wolf3d... maybe some game that was almost OK will be better with the 486slc cpu... or some utility or something
If you have any benchmark request tell me before I pack the systems again 🤣

Glad to see the upgrade having gone that well. Thank you, keropi, for taking the time to experiment even down to risking your own hardware. Really glad to see our efforts paid off.

This opens door for anyone having a MegaPC and wanting a 486SLC upgrade, even though the performance increase is really marginal. But it's at least enough to make some programs and demos run better. Fasttracker II and the Crystal Dream II demo (both from Triton) actually benefit from this upgrade. No need to hunt down a 486SLC-80 motherboard now.

@Dioxaz
well it is only because you share the info this upgrade was possible 😀

So rare to see all WDC chipsets and video chipset.

I wondered why computer makers didn't go for that.

Cheers,

@keropi.. how does Doom fare on the 486 in comparison?... just wondering if it would take advantage of the cache in any way..

phipscube wrote on 2020-09-30, 09:06:

@keropi.. how does Doom fare on the 486 in comparison?... just wondering if it would take advantage of the cache in any way..

it's crap man 🤣
it behaves just like it on a 386DX40 system , pretty unplayable and you have to use low detail mode... I can bench later if you are interested in frames

keropi wrote on 2020-09-30, 09:20:

phipscube wrote on 2020-09-30, 09:06:

@keropi.. how does Doom fare on the 486 in comparison?... just wondering if it would take advantage of the cache in any way..

it's crap man 🤣
it behaves just like it on a 386DX40 system , pretty unplayable and you have to use low detail mode... I can bench later if you are interested in frames

Yes have found too that the original version of Doom is pretty poor on the 486SLC, however....

When using the FastDOOM port (on this forum) I've found its actually quite playable on the 33Mhz 486 and you don't have to turn off too much (nor resort to Potato mode...) 😀 - must admit to wishing the developer produces a FastDoom Heretic port, as that would be amazing. I've also tried FastDOOM on a 386SX which did struggle more on the same settings - thus the 486 is certainly an performance improvement - abet only for some/optimised games !

That means its worse than a 486sx25.. but still a little better than the 386sx25... ok benchmark it just for a laugh 😁

Edit:- what about X-Wing?...
Edit 2:- does the 486 aware BIOS recognise HDD above 500MB? And allow booting from CD?

phipscube wrote on 2020-09-30, 10:21:

That means its worse than a 486sx25.. but still a little better than the 386sx25... ok benchmark it just for a laugh 😁

Edit:- what about X-Wing?...
Edit 2:- does the 486 aware BIOS recognise HDD above 500MB? And allow booting from CD?

Using Phil's benchmark suite and DOOM in fullest screen:
- low detail mode: 14.07 fps
- high detail mode: 8.70 fps

no the stock 486slc bios has that 512mb limit - cdrom I have no idea there is no place to put one in the system but tbh I doubt it can boot from one. Remember this is basically a 386DX-type system/bios
and no idea about x-wing, I don't play that game to make comparisons 🤣

I finally have my Mega PC! I've stripped it down and checked everything. The battery has caused mild damage which has taken out the funtionality of the floppy drive, but the HDD works perfectly and is still loaded with the stock software!

I will take off the floppy and HDD headers and check all traces, then replace with new ones

It came with 3 manuals from the 486slc, they didn't get thrown away at least.

Here it is all set up with Sonic looking well snazzy! 😁

Booted to the Amstrad Desktop on the BenQ monitor

The battery leak damage

And the full board

very nice!!!! one more to the club!
you can use the EXT.BATERRY header and put one sealed in some baggie or something away from mobo
that 486SLC33 tech. reference is it a service manual?

I'm looking at putting one of those CR2032 adapters from Amiga kit in with the diode to stop the charge circuit..

The "Technical reference" looks just like a regular Mainboard setup user manual. No schematics or anything..

Here's some pages to show you..

ah interesting
the manual mentions cache utilities, too bad I assume you don't have the disks anymore?
good idea about the battery to use the amigakit thing

@Keropi, unfortunately I don't have the disks.. I can't remember if I ever did..

I could scan all these manuals if you'd like to read them? If anyone else would like them too?...

phipscube wrote on 2020-11-24, 09:49:

I could scan all these manuals if you'd like to read them? If anyone else would like them too?...

Yes Please !

Glad you got it back safely and the HDD is all ok, fingers crossed your repairs will get the FDD back working.
Very interesting about the 7486 Cache utility - hopefully someone out there will have a copy of that original amstrad disk.......

Some recent developments on my side to inspire you - Christmas came a little early for me (ok birthday 😉 ) and my partner got me a Mega Everdrive Pro ! - it works beautifully on the MegaPC, so I can now have SegaCD games on the MegaPC without a MegaCD and the required uber rare Amstrad link cable.

The PC side hasn't been neglected and now sports a rather nice Reptile Paradise - Yucatan FX board - Midi has never sounded better on the MegaPC !