Quick PSX video mod (correct output on both NTSC and PAL)

This only works with certain specific PU-8 boards (1-658-467-4x work for sure, maybe others) - but it will give you a machine that will correctly play both PAL and NTSC discs over any of the video outputs. I did this on a PAL debug machine, and the result is a console that will play both originals and copies from any region with correct color encoding.

The basic issue is that the GPU has two different clock inputs - one is used for PAL and the other for NTSC, and they need to be different frequencies. On the early boards, the two input pins were simply connected together and the correct oscillator module was installed on the board, resulting in one video mode working correctly and the other generating signals that were off-frequency. At some point in the production of the PU-8 boards, the layout was changed so that both oscillators could be installed, and a jumper added to the layout that connected both the inputs together.

My guess is that this change was made because of the yaroze machines, which were officially multi-standard and had both the NTSC and PAL clock xtals fitted to support this. For the regular machines made with the same board, they just fitted one of them and installed the link on the back of the board to connect it to both of the inputs on the chip.

First of all, check to make sure that the circuitry below IC203 looks like this:

This is a PAL board, so the left oscillator is the one installed - on a NTSC machine, it will be the one on the right.



Now, just install the other oscillator, the output resistor (220R) and the little ferrite bead for the power supply.



Finally, turn the board over and remove this green zero ohm link:

 

On NTSC machines the green resistor is populated at the top right position, causing the PAL clock input to be grounded. Enabling 50Hz causes the GPU to stall, crashing the system and nulling the video output.

 

Thank you for pointing that out - looking at the board I also realized that I needed to install another decoupling cap, although the machine seemed to be working fine without it.

Photos of an (unmodified) NTSC PU-8 (1-658-467-41) PCB:

 

Interenzing , but only working psx pal or ntsc?.

Not clean me, i have psx ntsc fat.

sorry for my bad english XD.

 

Only a couple of my NTSC units behave like this, others are fine.

 

That's because only GPUs with dual clock sources are like that. And that feature is specific to the PU8 board with the 208 pins GPU.