No Video after MechaPwn with FMCB card installed - SCPH-50000 Model - Help?

[petuona]

Hi everyone, I could really use some help I’m pretty overwhelmed and stuck.

I have a Japanese SCPH-50000 (Midnight Blue BB Pack) PS2. I am in North America.

Here’s what I did and what’s happening:

• Console works normally with composite cable on CRT
• BB Service previously worked fine on my TV (composite, no issues), regular BIOS works without HDD installed.
• Installed FMCB memory card - HDD was connected during that time.
• Ran MechaPwn (newest version, off USB) - installed, went through all steps, unplugged twice and rebooted
• After that:
  • With FMCB inserted → no video on CRT over composite
  • If I remove both FMCB → video returns and BIOS shows fine
  • HDD doesn't seem to impact anything

Symptoms when video fails:

• Green power light
• Console seems to boot
• Sometimes brief white/grey flicker / shaking, some high pitch noises

Important constraints:

• I do not have access to another PS2
• I cannot launch homebrew without FMCB
• I’m using composite (yellow/red/white), not component or HDMI - I have a set of component cables on the way
• HDD is currently disconnected

My understanding:

• MechaPwn likely changed EEPROM video / region flags - ???
• FMCB or BB boot path is triggering an incompatible video mode - ???

What I’m asking:

• Best way to recover video with FMCB inserted
• Or, how to undo MechaPwn safely without another PS2
• Whether reinstalling FMCB / clearing config / EEPROM tools would help

What I've tried:

• Triangle/Circle/X hold at boot - nothing, just more flashes
• Switching YPbPr to RGB in system settings without FMCB card in - no change
• Unplugging HDD/USB etc.

Thanks all

Edit: Tried PS2 NTSC-U disc without FMCB Card in... and it worked?

My goal though is playing backups etc...

Edit 2: Current theory... Pre-Formatted MC I bought wasn't Cross-Region enabled

Edit 3:

SO

After running MechaPwn 3.0 RC4 (only RC4, never RC3) from USB with an FMCB memory card inserted, I lost video only when the FMCB card is present. Video returns immediately if the memory card is removed, and original NTSC-U discs boot fine, so hardware isn’t damaged and the region unlock worked?? RC4’s release notes warn that it may corrupt memory cards and that FMCB must be cross-region, otherwise FMCB autoboot can stop working. My FMCB card was a preloaded NTSC-U/Amazon card and maybe not cross-region, so RC4’s mechacon/NVRAM changes appear to have caused some sort of FMCB autoboot + video mode mismatch on this non-Deckard (50k) console.

Plan:

Going to try FreeHDBoot and see if that just solves everything.

Thought about buying the SD card based memory cards, but didn't really need the features outside of FMCB.

Or... I could blind restore defaults to MechaPwn with no visuals just controller input XD