VOLTAGE MOD UPDATE: SUCCESS!
CORE
Thanks to
@M4j0r we know know what offset to change the RSX CORE Voltage ID (VID) on Mullion SYSCON.
It requires a write to the SYSCON EEPROM via UART (Serial). I do not want to explain how just yet. I'm still working on the details and I want a change to try it out a bit before writing up a tutorial. I only just today mapped the VID table on the NCP5318's data sheet to the EEPROM Bytes that select any VID you want. But I did prove it works.
VID432105 | Vactual | Vmin (-0.5%)
001011 | 0.926v | 0.9263
001101 | 0.901v | 0.9015
110001 | 1.223v | 1.2248
001010 | 0.937v | 0.9388
Proof of concept was on an A01 Frankie. The 90nm RSX was replaced with a 40nm pull that failed in such a way that it's the perfect test bed for this. It was artifacting in stress testing (bad RSX) but not dead completely. This means I can burn it out and it won't matter. It needs replaced anyway.
To be clear. This only works on Mullion SYSCON so far. We have not located the appropriate offset in Sherwood SYSCONs. Which means we can't use it on Slims yet. I've only tested it on a COK-001 (CECH-A01). These consoles unmodified do not overclock well at all! But frankies OC fine. I have one with a 40nm that does 800/950. Now that I know what I'm doing, I'm keen to try overclocking it to see if I can stabilize 850 Core.
VRAM
Thanks to @b_rob1 we were able to Potentiometer mod the VRAM voltage (FBVDDQ). I tested it in a console that was fine 25MHz earlier, and then almost bricked. I increased voltage from 1.8v to 2v and while it was hotter, it wasn't more stable. Not in the least. SO I have concluded VRAM voltage mods are pointless.