willmurray461 wrote on 2024-07-24, 16:27:

Also, I remember reading somewhere that there may exist IBM 5x86C chips with core designs outside of Stepping 0, Revision 5 and Stepping 1, Revision 3. Has anyone actually found one?

I've never heard of something other than Stepping 0, Revision 5 and Stepping 1, Revision 3. I think that's just one of those myths no one can prove just as that John Davis once pronounced “camry” correctly

feipoa wrote on 2025-07-17, 02:40:

My interposers all had i486DX4-100 WT chips on them. They work fine with Cx5x86 and Am5x86 CPUs. If you can find some from China, they are usually very cheap. I sent my contact a message of inquiry about more.

Message me if you hear back. Sounds like an Evergreen Technologies 586 AMD 5X86 upgrade chip could work as well, yes? I imagine you use a hot air station to remove the original chip?

feipoa wrote on 2025-07-17, 02:40:

My interposers all had i486DX4-100 WT chips on them. They work fine with Cx5x86 and Am5x86 CPUs. If you can find some from China, they are usually very cheap. I sent my contact a message of inquiry about more.

So far, my contact has not replied, but he read the message. Either he is still trying to find the interposers, or he isn't interested. Will wait another week, then message him once more.

douglar wrote on 2025-07-23, 01:31:

Message me if you hear back. Sounds like an Evergreen Technologies 586 AMD 5X86 upgrade chip could work as well, yes? I imagine you use a hot air station to remove the original chip?

I doubt those would work, for 2 reasons.

1) most of those Evergreen interposers contain a 1117 VRM, which normally maxes out at 800 mA (some brands note 1 A). According to the IBM 5x86C 3.3V Microprocessor QFP Addendum (Fax #40045), at 100 MHz the minimum current draw is 0.8 A, and max is 1.1 A. How much does the Cx5x86 draw at 150 MHz and, say, 3.7 V? Probably over 1.5 A.

2) those Evergreen interposers have the VRM set to 3.45 V. You would need to modify the interposer with a trimmer to go over 3.45 V. I have done this on one of my Evergreen modules, as well as swapped the VRM for a beefier unit (maybe 3 A). Howvever, there were several revisions of the Evergreen Am5x86 interposer and not all of them have the solder pads for the larger VRM.

Looking into this a tad further, I wanted to see which VRM's were used on interposers containing IBM/Cyrix 5x86 chips.

Gainbery interposer with QFP Cyrix 5x86-100QP
contains 2955 MOSFET = 2.5 A

Gainbery interposer with PGA IBM 5x86-100HF
contains LT1528 = 3 A

Evergreen, with a PGA Cyrix 5x86-133/4x
EZ1086CM = 1.5 A

If you are considering using an Evergreen QFP-PGA interposer and want to upgrade the 1117 VRM, I used an LD1085 w/trimmer on a few of my interposer. However, I've only run them with Am5x86 chips.