The Mayumi v5.1 was a modchip developed specifically for the PSone (PM-41 and PM-41 (2) boards), it was based on the Mayumi v4. The code runs on PIC12C50x chips.

There isn’t a ton of information about this chip out there online, so if you have any information about this chip please let me know so I can update this guide.

This chip has several modes that can be changed by having the CD door open for at least five seconds when you press the power button. It defaults to having the modchip enabled. An LED can be hooked up to the chip to indicate which mode is active.

Mode toggle flow:

1. PSone mode (default)
2. Modchip disabled

The mode LED is connected to pin two of the modchip. Connect the LED to VCC (pin 1, 3.5V) through a resistor, and then connect the ground side of the LED to pin 2 of the modchip.

Because the chip uses the internal PIC oscillator instead of the oscillator from the console it may not actually be as desirable as the Mayumi v4, even in a PSone. One advantage is that it needs less wiring.

This modchip also doesn’t do any BIOS patching, so it isn’t very useful in PAL PSones which have the additional BIOS lockout of non-PAL games.

Hex code:

• Coming soon.

PM-41 board diagrams