Dell Latitude 3510 – Same keyboard keys not working after replacing keyboard, palm rest, AND motherboard (losing my mind)

The problem

A specific group of keys does not work at all:

• O
• L
• 9
• And a few others in the same vertical/diagonal line

They do NOT work:

• In Windows
• In BIOS
• In Dell diagnostics
  So this is not an OS or driver issue.

What I’ve already replaced / tested

I’ve gone way beyond basic troubleshooting:

• Replaced the entire keyboard
  
• • On this model, the keyboard is fused/melted into the palm rest, so I replaced the entire palm rest assembly
• I now have 2 different palm rests / keyboards
• Replaced the entire motherboard
  
• • I now have 2 different motherboards
• Tested:
  
• • Keyboard + motherboard outside the chassis
  • With and without battery
  • With minimal components connected
• Reseated keyboard ribbon multiple times
• Cleaned connector with isopropyl alcohol
• Updated BIOS (normal update and recovery)
• Loaded BIOS defaults
• Swapped parts in every possible combination

Result:

No matter what combination I use:

• Keyboard A + Motherboard A → same keys dead
• Keyboard A + Motherboard B → same keys dead
• Keyboard B + Motherboard A → same keys dead
• Keyboard B + Motherboard B → same keys dead

The failure pattern is IDENTICAL every time.

Why I’m confused

• Two different keyboards
• Two different motherboards
• Tested outside the chassis (no pressure issues)
• Same exact keys always fail

This makes it feel impossible that:

• Both keyboards are bad in the same matrix line
• Both motherboards have the same defect

But that’s what I’m seeing in real life.

Things I’m wondering

• Is there any known Dell Latitude 3510 keyboard matrix issue?
• Can a BIOS / EC firmware corrupt keyboard matrix mapping permanently?
• Is it possible for a motherboard to damage a keyboard matrix line and then the keyboard stays “dead” even on another board?
• Is there some model-specific keyboard revision / incompatibility that causes this exact behavior?
• Would downgrading BIOS or reflashing EC firmware make sense here?
• Is there something outside the keyboard/motherboard (firmware, EC config, etc.) that I’m missing?