OK, that's a really useful error.
The VRAM2K is sometimes also called FAST VRAM, or HIGH (speed) VRAM - but for today lets call it VRAM 2K
This site will show you where abouts on the MV6 board those 2K VRAM chips are located (in the top right)
https://github.com/jwestfall69/neogeo-diag-bios/blob/master/docs/ram_locations/mv6.md
So if you want to pull the 2K VRAM chips and replace them with known good ones you can do that, but in my experience it has never once helped. For me not has always been either bad addressing or rotten traces in/out.
But swapping the chips easy to do (they are DIP, not surface mount), and good practise, so maybe give that a go.
After that doesn't work we could try some other stuff
The NeoGeo Dev wiki shows the graphics pipeline here
https://wiki.neogeodev.org/index.php?title=Graphics_pipeline
Confusingly the 2K VRAM is called HIGH (Speed) VRAM in this diagram, just one of those things we are expected to know.
Anyhoo, the point is that the 2K VRAM talks only to a chip called LSPC which does all the line sprite control
There are two versions of the LSPC chip, but the 6-slot boards used one called LSPC-A0. You can check the pinout for LSPC-AO here
https://wiki.neogeodev.org/index.php?title=LSPC-A0
The pins that we are most interested in on the LSPC are the ones associated with the Fast VRAM address bus (see! Now the 2K VRAM has another name now, how annoying is that?!) and the Fast VRAM data Bus
Address bus = FVA0 to FVA10
Data bus = FVD0 to FVD15
We can look those up on the pinout and see the
the FVA lines are pins 139 to 149 on the LSPC
the FVD lines are pins 60 to 75 on the LSPC
Then we can look up the pinout for the 2k VRAM and see where those address and data lines go
Of course to look up the pinout for the 2K VRAM we first need to know what chip it is, You could visually inspect it, or look at this list here
https://wiki.neogeodev.org/index.php?title=RAM_chip#MV-6
And see that FAST VIDEO = CXK5814P-35L
So you could look up the pinout here
https://html.alldatasheet.com/html-pdf/47128/SONY/CXK5814P-35L/86/1/CXK5814P-35L.html
And see that
there are 11 address lines - these match FVA0 to FVA10 and are common across both VRAM 2K chips
there are 8 data lines - the first 8 match FVD0-7 on one of the 2k VRAM chips, and the other 8 match FVD8-15 on the other 2K VRAM chip
At that point you can beep out all of the lines on the LSPC and make sure they are going to the right place with continuity on the 2KVRAM chips
And without a logic probe that's all you can do
If you do get a logic probe you can check that the signals are being sent correctly
Address bus = FVA0 to FVA10 = should all be PULSE all the time
Data bus = FVD0 to FVD15 should all be PULSE all the time
Chip enable should pulse on boot then sit LOW
Write enable should pulse on boot then sit LOW
Output enable should pulse on boot then sit LOW
At that point we will know if the problem is indeed With the 2k VRAM per the diagnostics bios. or if this is just a symptom and we need to look further up the graphics chain for the root cause
