• Please review our updated Terms and Rules here

AST Advantage 486 - upgrade potential?

C

commodorejohn

Veteran Member
Joined
Jul 6, 2010
Messages
3,311
Location
California, USA
I've just got a decent little 486 system and I've been looking it over. It's this board, and it has an empty socket in addition to its surface-mounted 486SX; that's the socket in the illustration, which I figured was for a 487. I see from the page that this board supports 486DX and DX2 (as well as Pentium Overdrive,) but what I'm not clear on is whether that means there's versions of this board that come with a 486DX, or whether a 486DX can be installed in the socket.

Does anyone know if I can grab a 486DX and drop it in the socket, set the jumpers correctly, and have it work? Am I risking anything by trying?
 
Yep, just stick a 486DX in the socket and it will work if the jumpers are set correctly.
In the jumpers table you linked, the 486SX (PQFP) option is for the CPU mounted on the motherboard, while 486SX (PGA) refers to one in the socket.
 
Ive got the twin to yours commodorejohn.. Mine had the Overdrive DX266 upgrade in it. Shes running openstep 4.2 on a 1GB HDD.. Quite a neat machine..

Glad this one got over there safely in one piece.. Enjoy it. I know i like mine
 
Yeah, I've got a 486DX2-66 lined up for mine. Should improve things a bit. I may max out the RAM at some point, but I think 24MB should be plenty sufficient for now ;)
 
I had a couple of those AST Advantage 486's back in the day, they were great solid and stable machines. But a pain in the butt to get to get the cover to snap back on ;-)

I had DX50's in all but one of mine, I want to say that one only had an SX25, what CPU is soldered in yours?
 
Okay, the DX2 got here today. The first thing I noticed is that it's actually smaller than the socket, but I gathered from some quick research that this is common for 486 upgrades, and that I can just drop it into place in the middle of the socket. So I did, it fits okay, and I believe I've got it oriented correctly (the notch on the ceramic aligns with the corner with the extra pin in the middle on the socket.) I've got the jumpers in place as that page says they should be for use with this.

So I power it on and it takes power, flashes the keyboard LEDs, spins up the drive, and...nothing. No video, keyboard lights don't respond to the appropriate keypresses, not even a POST beep. Have I made a miscalculation, and this isn't actually compatible after all?
 
Is there a jumper to disable the onboard CPU? If not, the other option is to find a "487SX" upgrade chip, which has the CPU disable pin, or find an "overdrive" branded DX2.
 
I don't know, the page doesn't list what the jumpers are, just what to set them to for a particular CPU. Pity this didn't come with a manual...wonder if I can find one online...

Is the CPU disable pin the extra one just inside the middle of the PGA socket? If I leave a wire snippet in there, would that disable it?
 
commodorejohn said:
I don't know, the page doesn't list what the jumpers are, just what to set them to for a particular CPU. Pity this didn't come with a manual...wonder if I can find one online...

Is the CPU disable pin the extra one just inside the middle of the PGA socket? If I leave a wire snippet in there, would that disable it?
Click to expand...
I seem to recall a jumper but its been so long it escapes me for sure if that's how it worked.

It would take more than a wire snippet in the pin, and I don't know what pin number the disable pin is, nor if that pin would have to either be pulled high or low (depending on design of the CPU disable pin), I honestly don't know which, but maybe someone else on here would know and could answer that.
 
Last edited:
I can't find the 487sx pinout anywhere (don't think Intel ever published it, but I may be wrong). The extra pin inward of a corner may be it, or not; chances are it probably is.

Again working with probabilities, chances are it needs to be pulled low through a resistor. You could insert a wire in it, install the CPU on top, turn the computer on then with a high impedance multimeter measure the voltage on that pin. If it's +5V, you could try to pull it to ground by a 5-10K resistor and see what happens. Worst that could happen is you fry the motherboard and CPU though, so take all I said with a grain of salt.

(edit) I actually managed to find a datasheet which shows both the 486sx and 487sx pinouts at http://www.datasheetarchive.com/dl/Datasheets-112/DSAP0042446.pdf

It turns out that the "extra" out-of-alignment pin is not electrically connected and is just used as a key for correct orientation. The pin that disables the 486sx is called MP# on the 487, and is located at B14. It needs to be driven low (ground) to disable the 486sx. It is not connected on the 486sx. However, on the 486DX that pin is called UP#, and when pulled low it will disable the CPU. This way you can only use a 487sx to upgrade a 486sx system, not a 486dx (because it will get disabled itself)

So in conclusion I would try this: pull low pin B14 on the socket, but electrically insulate the same pin on the 486dx CPU so it doesn't get disabled itself... One way to do this would be to cut the B14 pin on the CPU if you dare. Standard disclaimer applies, do it at your own risk.

(later edit) Here's a patent that has some more information in it. http://www.patents.com/us-5473766.html (wish I could upload it as attachment... it's only a 600k PDF, but the forum limits PDFs to 48k which is not useful)
 
Last edited:
Figured it out, I hadn't pushed it far enough into the socket. Nice of them to not use a ZIF socket for a giant PGA chip :/ Anyway, with CPU firmly seated and jumpers set, it works just perfectly.
 
commodorejohn said:
Figured it out, I hadn't pushed it far enough into the socket. Nice of them to not use a ZIF socket for a giant PGA chip :/ Anyway, with CPU firmly seated and jumpers set, it works just perfectly.
Click to expand...
I know the feeling my Compaq CDTV 520 is also a NON-ZIF socket, makes me feel like I am going to break it every time I pull or insert the chip.
 
That is true, the Non-ZIF sockets are the worst ever made, I've got an embedded board that I use for testing my Pentiums and Pentium MMX's and every time I shove something into it I feel like I may bend a pin shoving it in or worse, break the chip itself.
 
commodorejohn said:
Figured it out, I hadn't pushed it far enough into the socket. Nice of them to not use a ZIF socket for a giant PGA chip :/ Anyway, with CPU firmly seated and jumpers set, it works just perfectly.
Click to expand...

So what do YOU do with it?

I have the same machine I've used for what -- 20 years? in my business. It's key to all my work. Windows is so much less productive. DOS rocks on the later machines, so I use DOS windows (i.e., in XP); but the only way I can use my old Borland Sidekick (which runs my business merge software), is on the 486 and 386 machines.
 
I use it mainly for DOS gaming, though I hope to use it for a testing machine for some game development eventually :) Seems like a decent machine, all told - I'm a bit impressed that it can take all the way up to 32MB of RAM!
 
Uh, I said above that I got it working - I just hadn't pushed it in far enough. Silly me, I assumed that the point of significant physical resistance would be the point at which I was supposed to stop pushing :/
 
You must log in or register to reply here.
Back
Top