Hi all - I have one of these http://www.uktsupport.co.uk/acer/mb/aca1gx1.htm and have been given an AM486 DX5-133W16DGC processor. With the jumper settings do I need to set it to a Pentium overdrive or an AM486x2 ?
For a 5x86 you need to use the settings for "Enhanced AMD DX4 SV8B(WB)", but you'll also have to find a jumper that switches the CPU internal multiplier to x2 (which works as x4 for the 5x86) instead of the default x3. Otherwise you'll run at 100MHz (33x3) instead of 133 (33x4).
It doesn't seem to be documented in those settings, so it may be necessary to trace the CLKMUL pin of the CPU with a multimeter.
I bet the Enhanced AMD DX2 SV8B(WB) settings will work--only one jumper is different than the DX4 and that's likely the multiplier. In any case, neither of the AMD Enhanced DX2 WB or AMD Enhanced DX4 WB will break anything if you try them.
edit: are you sure you have also changed the voltage to 3.3V?
Thanks both - I will put it on both and see if it boots. I need to work out the jumper for the voltage.
Well, some boards do need to have bios support. My MSI runs a DX4 at the moment (on an interposer). Three interposer has all the settings available to run with both the AMD and Cyrix 5x86. The spare Am5x86 I have, makes the board look quite dead. The CPU itself runs great by three way, on another board.
Stuck at 10MHz...
waterbeesje wrote on 2021-09-23, 18:06:Well, some boards do need to have bios support. My MSI runs a DX4 at the moment (on an interposer). Three interposer has all the settings available to run with both the AMD and Cyrix 5x86. The spare Am5x86 I have, makes the board look quite dead. The CPU itself runs great by three way, on another board.
Do you have your BIOS image somewhere?
What if you use an Am5x86, but jumper it so it runs at a multiplier of 3? That might narrow it down to whether it is the speed or CPUID breaking things.
jakethompson1 wrote on 2021-09-24, 01:09:waterbeesje wrote on 2021-09-23, 18:06:Well, some boards do need to have bios support. My MSI runs a DX4 at the moment (on an interposer). Three interposer has all the settings available to run with both the AMD and Cyrix 5x86. The spare Am5x86 I have, makes the board look quite dead. The CPU itself runs great by three way, on another board.
Do you have your BIOS image somewhere?
What if you use an Am5x86, but jumper it so it runs at a multiplier of 3? That might narrow it down to whether it is the speed or CPUID breaking things.
Yes i have dumped it in another thread, but it appeared to be corrupted according to the experts here. I did read thru it, and saw the dx4 mentioned, but not the 5x86 (or dx5 if you like). Gonna dump it with an EPROM writer some day, when I've got the time to do it.
On the other hand: my Aquarius MB4DUV does take the Cx5x86 and Am5x86 for granted. It supports the settings in the board, but the BIOS reports a 486 SX66 (not even sx2-66) so that's a mess... But it does work like it should 😀
So there's always hope a CPU will work, even the bios doesn't know it. It's a matter of luck I guess.
Stuck at 10MHz...
