Wiring of the new bios went well. Next step is to install the Mayumi v4
Quick one...should I install a pull-up resistor on A19 mother board side since it is unused and in floating state?

Pictures of the new bios

Thanks

Thanks for your reply, I think a 10kohm resistor will work well as a pull-up.
Can I assume that IC102 pinout from SCPH-7500 is similar to SCPH-5500 / SCPH-7000 ?

Has the bios pinout (IC102) for motherboard UP-18 & UP-20 been mapped before?
I plan to install a package PLCC32 - SST39VF040. Not sure what to do with pin31/WE
Thanks

Thanks for the information, replacing the bios chip is I think the best solution.
The system seems to supply 3.5v which limits the range of chips that can be used.
Is there a list of suitable chip? From what I read on the forum and based on datasheet 29LV040, 27C512 would work.
Thanks

Hi, this is my first post on the forum. I own a SCPH-5500 / UP-18 (JP) and a SCPH-7000 / UP-20 (JP) for which I have installed and swapped 2 modchip (Mayumi v4 and MM3) but could not get to load a PAL or NTSC/U game so far. From what I gathered it is not possible to region mod a jpn PS1 regardless o...