On the MV1FZ sync is outputted from pin 150 of GU2 (LSPC2). From there it goes to pin 1,2 of U1 (74LS32) and from pin 3 of U1 to jamma P with 100 ohm resistor in series and 470 ohm resistor to 5v. Lift pin 1,2 of U1 from the PCB and tap sync from the vias just before those pins, after checking continuity with GU2 (150). If the picture keeps rolling either the LSPC2 is faulty or your monitor/TV can't handle the sync signal (50hz only PAL TV??). If the picture syncs OK then it's the LS32 that is faulty.
I watched your video: can you get games to display with carts inserted or is it stuck in hardware test?
GOD BLESS YOU
With your info, i found that there was no continuity, from U1 (74LS32) and pin 150 of GU2, one of the tracks was cut, i solder a very small wire from those 2 points (uffffff that was HARD...)
Also put two new caps of 470 uF at 16v, the older ones, were bad
I now have a very good picture
THANK YOU
BUT... The sound is terrible, very low, and with very interferences and some strange Sounds, even with the mobo volume at max, and the tv volume at max, the volume is low, and with some strange sounds
It's life, one problem fixed, a new one just come
Thank you very mutch
YOU SAVE ME FROM GOING (EVEN) MORE INSANE