Section 1-12 of the Service Manual indicates T6950 as CRT controller for the 501P
Section 4-05 of the Service Manual gives technical details about T6950
The indications on the PCB are very clear :
Besides, according to the manual, only the RGB unit of the 501F (with TMS9129NL) can be adjusted. So, it does not seem possible with the T6950, used in the 501P.
This is not a good idea to group models of different countries on a single page. This gives no advantage. It gets messy for pictures. And what to do with the screenshots of the different firmwares, with advertisements and with specific upgrades links when there are? If we want found information on a french model we go to a oage with many useless information. Now the HB-F700D, HB-F700F, HB-F700P and HB-F700S are grouped on the HB-F700 page but the MSX2 HB-F700 does not exist. It's also less convenient if we want compare models pictures. It's a shame this wiki had become the best of the web. 