So the P54CS SY045 CPU (i200) arrived and it works just fine at 1.5x and 2x 66 MHz. The BIOS report it as P100 while running at 133 MHz.

At 2.5x and 3.0x multiplier it does not POST. Time for the trusty POST code analyzer --> no code.

Could a BIOS update do anything about this situation or other aspects at play?

JP2 and JP3 goes to BF0 and BF1 respectively. JP1 goes to PICD1. Jumper closed means tied to GND for these three.

EDIT: My bad, JP3 goes to STPCLK# so no wonder it does not run with this jumper closed. Interesting design choice... 🤔

So need to ground BF1 then. Will try to install this neatly with a switch or similar.

Yes, I think those really old socket five motherboards didn’t do the multiplier pins correctly so make sure that you have proper pull ups and pull downs for BF0 and BF1

Socket 5/7/SS7 (Motherboard) Tweaker (Released)

It’s easiest to mod the top of the cpu with smd resistors.

But if you feel up to it I could use help designing the board for adding switches and resistors to the back of the sockets. I’ve pretty much got the design figured out it seems, just need someone to help make the gerber

Sphere478 wrote on 2022-03-28, 23:10:

Yes, I think those really old socket five motherboards didn’t do the multiplier pins correctly so make sure that you have proper […]
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Yes, I think those really old socket five motherboards didn’t do the multiplier pins correctly so make sure that you have proper pull ups and pull downs for BF0 and BF1

Socket 5/7/SS7 (Motherboard) Tweaker (Released)

It’s easiest to mod the top of the cpu with smd resistors.

But if you feel up to it I could use help designing the board for adding switches and resistors to the back of the sockets. I’ve pretty much got the design figured out it seems, just need someone to help make the gerber

Yes I have been following your thread and it is indeed a great source of information, I would be glad to help out in any way I can! Eagle CAD / Gerber files you say... that was not yesterday =)

In fact I also have a parallel system/project going on with an early Socket 7 (430HX) DTK/Gemlight GMB-P55IPS-V0 board, which needs to be retrofitted with both a VRM for VCC2 pins, as well as proper pull-up resistors for BF0 and BF1 to enable 3.0x and 3.5x multiplier for MMX CPU support (will create a separate thread for this once I get going) 😀

sweet! I've posted some updates. but am kinda stumped. catsay says I did it all wrong 🤣 apparently I messed up the spacing and traces somehow. anywho, see ya in the thread :p thanks!