Hi,

I'm an old Vogons follower but a new member of the Vogons. Greetings to all of you.

I have an AT&T Globalyst 515 desktop computer with 486 Dx33 and 12Mb ram installed. In my Windows 3.11 and PC-DOS 7.0 system, it seems everything works fine. When i want to downgrade it to SX25 with correct jumper settings according to configuration document, It gets strange. Yesterday i tried different CPU's with this motherboard (with correct jumper settings) and i got different results.

1- 486 dx33 - Works fine.
2-486 dx2 66 WB - After post, no boot.
3- Cyrix dx2 66 - In the post, CPU shown as Cyrix DX2 75Mhz, it boots.
4-486 sx25 - In the post, CPU shown as "DX" 25 Mhz, everytime it wants me F1 to enter setup, after exitting setup, system boots normally. eg. Excel 5.0 normally says no co-processor present.

I can change only 3 jumper settings according to this site. https://stason.org/TULARC/pc/motherboards/A/A … BALYST-510.html, other jumpers were undocumented or removed from pcb and a jumper array was factory soldered. I tried 2 different bioses. One from NCR and other from FIC. Nothing changed.

Today I installed my dx33 again and run diagnostics floppy from NCR. It passes every test (Memory, CPU, Keyboard, Floppy, VGA, Ports etc..) except "Numeric Processor" test. Like this;

__Functions on 80486 Floating Point Unit
PASSED
__Exception and Condition bits on 80486 Floating Point Unit
-Exception Interrupt missing - System HALTED

So guys, what's wrong with this motherboard ? Bad caps, bad logic, bad chipset etc ? I need help.
Thank you very much.