Info on 386 to 486 Upgrade cpus please

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limboy777

limboy777

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Hi all

I have a few Amstrad Mega PC's. One of them upgraded to 486 50mhz using a cyrix chip (Same as the SRX chip) I recently installed a new HDD and managed to get the cache and chips working using software supplied by a fellow Amibayer

Im looking for information what other chips could be used to upgrade a 386 sx 25. I dont mind if they have a large heatsink on top as I think the mega pc floppy/hdd cradle could be modified to accommodate.

I have heard of the IBM Blue lightning and apparently it is the fastest upgrade chip but dont know if this would work on an SX as some chips are particular to 386 DX models etc.

Any help would be appreciated.:thumbsup:
 
I have investigated the same in the past... there are some upgrade chips with IBM's "486slc" (in quotes bevause they are vastly superior to the cyrix ones since IBM ultra-finetuned the architecture) BUT they are almost impossible to find. I never saw one for sale and the only IBM 486slc cpus I have seen are soldered at IBM's motherboards...
Basically we are stuck with the 486slc2 (and similar) upgrades...
If you ever manage to get an IBM upgrade it will work just like the cyrix one: by disabling the soldered cpu and using double/triple internal speed.
Personally I gave up searching some ~2 years ago...
 
I have a Cyrix486SLC2@50MHz CPU. On my A2386 bridgeboard, Norton Sysinfo rates it as powerful as a 486DX33. About 4 times better than the original 386sx@25MHz. The 1KB cache needs to be activated by software in autoexec.bat. However it does run hot. The advantage is that i have been able to use a Math&Co 387FPU with it.
There are also some 486SLC3 able to run at 75MHz but i have never found one.
If you are willing to solder to install such a CPU, i have a new Texas Instrument 486SLC@25MHz available for swap. It has a 1KB cache similar to the Cyrix one.
As for the IBM Blue Lightning, several CPUs bear that name. Some of them are 486SLC3 CPU with a 8KB cache: that's why they are better than the Cyrix/Texas. I am unsure they have been sold as clip-on upgrade, but they can be found soldered on some IBM mobo.
 
I have the Cyrix 486 DX2 50 with 1k cache and have the software thank to Keropi.

Has anyone got a picture of the IBM SLC chip so I can see what I am looking for.:thumbsup: (The only ones I can see are the normal processors) The clip on types must look similiar to mine?
 
they look like 386sx chips:

EvergreenIBM-Cyrix-286-upgrade-L.jpg


also check this: http://redhill.net.au/c/c-4.html#slc2 and since you are there check the rest of the stuff on the article, it holds some GREAT info! index is here: http://redhill.net.au/ig.html
 
limboy777 said:
I have the Cyrix 486 DX2 50 with 1k cache and have the software thank to Keropi.

Has anyone got a picture of the IBM SLC chip so I can see what I am looking for.:thumbsup: (The only ones I can see are the normal processors) The clip on types must look similiar to mine?
Click to expand...
Hi limboy777,
try this site CPU World --->Link
 
@lopos2000

these are 387 fpu chips , not 486slc cpu ones
 
Thanks for all your replies and the awesome links:thumbsup: Reading through now..

One more question, can I use any 387 or 487 co-processor with my mega pc or does I have to look out for anything.

Another chap on another forum is using a 33mhz co pro with a 25mhz mega pc.

I also read somewhere that 487's were actually 387 co processors but just renamed as a marketing gimmick?
 
On the megapc you can use a 387 fpu only, the 487fpu is another beast and is actually a full cpu+fpu chip that is used and the 486sx is disabled.
Also you can use higher clock 387 chips, they will downclock and work at 25mhz no prob!
 
Thanks for the reply. Just placed a bid on a 387 chip so fingers crossed
 
Apologies for dredging up an old(ish) thread but some useful info.

One thing is that almost all 486SLC/2 chips or above are 3.3V parts, not 5V parts. That's relevant because....

... I have now succeeded in my modification of one of my A2386SX bridgeboards.
No longer is it stuck at a lowly 25MHz cacheless 386SX. Now it's running at 50MHz 1K-cache Cyrix 486SLC/2-50. That's not a clip-on chip, I meant the board now runs just with the 486. Note that only the Cyrix 486SLC/2 chip will work like this, the IBM ones and the TI ones are 3.3V and will not work. Where did I get my 486SLC/2-50 from? The clip-on upgrade that I bought (I think from Keropi) for my Goldengate years ago!

In real terms it's exactly the same as the clip-on upgrades, but it's more reliable and even with the heatsink on, it fits within one expansion slot.
It's running Windows '95 fairly well and Doom runs quite nicely with a large window. Of course the RAM access is still slow, and the ISA bus bogs it down, but it's still cool. :)

Next step is to overclock the ISA bus..... 8MHz is too slow; I'm going to try 10MHz and 13.5MHz - my ISA cards are some of the later ones so they may well work... I hope. :)
 
Hi no problem with replying to this old thread.

Just to confirm, did you adapt an existing clip on upgrade and soldered it on a 386 board?
 
I just desoldered the 386sx from the bridgeboard, desoldered the 486slc2 from the upgrade, and soldered the slc2 directly onto the bridgeboard. Because it's a 5V part and not one of the upgrades with a voltage regulator (which are 3.3V) it worked perfectly first time.

Works a treat!
 
I have upgraded with a REV to 468 Adaper , running at 66/33 Mhz with adtitional headsink..., but only have 1 MB of Ram yet.
My Sim2ZIP Adapter ist not working yet, or i have the wrong RAM-Chips.
 
Did you replace the SCAMP chips too (the large square VLSI ones) or are they overclocked? They may need cooling at 33MHz if so. You replaced the crystal with a 66MHz one, yes?
 
Sry i overclocked to 60/30 Mhz and put Heatspreaders with thermal conductive glue onto the GAL's, VLSI Chips and Processor
 
I'd be interested to see some benchmark scores for your system! Any chance you could run the Doom timedemo? I.e. download the Doom demo and run "doom -timedemo demo3", making sure you have no sound or anything. Would be interesting to compare to my SLC2/50 with a 13.5MHz ISA bus...
 
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