P90 Platform Tuning

Table of Contents

[-0-]  Version History, Disclaimer & Legal Info
[-1-]  Precautions and Warnings before you start
[-2-]  Introduction to the Type 4 "Y" Pentium 90 Platform
[-3-]  The importance of cooling certain components
[-4-]  Modification A) Using a Pentium Overdrive 180 / 200
[-5-]  Modification B) Hardwiring the BF0 / BF1 Pins for different Bus / Core ratios
[-6-]  Modification C) Changing the Base Clock from 60 to 66 MHz
[-7-]  Modification D) Using a Pentium MMX 233 MHz with an Interposer
[-8-]  Problems, Workarounds and other stuff

Content by Peter H. Wendt (original HERE). Modified by Major Tom.

Modification A) Using a Pentium Overdrive 180 / 200

Note: This modification is compatible with all the other modifications explained here.

The Pentium Overdrive 180 and 200 processors are somewhat hard to find. They use the standard Socket 5 design with a single-rail 3.3 V power supply and use 50, 60 or 66 MHz base clock with internal 3x clock multiplier to achieve higher core frequencies. The Pentium Overdrive 180 / 200 chips have an integrated core voltage regulator and integrated clip-on cooling fan.

The Pentium Overdrive 180 has been designed as a drop-in replacement for the Pentium 90, 120 and 150 processors with the 60 MHz external clock. The Pentium Overdrive 200 is basically the same, but is designed for the 66 MHz bus. It was intended to substitute Pentium 100, 133 and 166.

Nicely thought out... but the P90 platform is not "Overdrive Ready".

Why? Because the integrated cooling fan requires a +5 V operating voltage to work. On the "Overdrive Ready" boards the two (normally unused) pins AN1 and AN3, which are marked "INC" (= Internally Not Connected) in the Intel datasheets for the Pentium P54C 75 - 200 MHz family, are connected to +5 V DC. On the P90 platform the two pins are not connected to anything - therefore the platform is not "Overdrive Ready"...

But that is simple to fix. All we have to do is to add a single wire connecting the two pins AN1 and AN3 to a source of +5 V DC. Like the + marked pad of capacitor C179 for example. And there you go, nothing else is needed.

POD Modification

If you think you could probably get a Pentium Overdrive 180 or 200 later, you could add this wire "just so" while you still have the soldering iron warmed up...

Content created and/or collected by:
Louis Ohland, Peter Wendt, William Walsh, David Beem, Tatsuo Sunagawa, Jim Shorney, Tim Clarke, Kevin Bowling, Tomáš Slavotínek, and many others.

Ardent Tool of Capitalism - MAD Edition! is maintained by Tomáš Slavotínek.
Last update: 13 Sep 2021 - Changes & Credits | Legal Info & Contact