After I finally found the cartridge to go with that trash-found PC Engine to use the CD-ROM, I got snatcher..
Everything works great, but I noticed something. Whenever the CD-ROM drive loads (laser moving), the picture has horizontal bands on the screen...
I checked the ground, they seem fine..
Bad capacitors either on the power supply or the voltage regulators (PC-Engine uses linear regulators like 7805 and 7809).
Probably they ran dry due to aging. Replacing them will fix the system.