Donkey Kong Jr bootleg - colour problem

[2001]

I have two Donkey Kong Jr boardsets (both bootlegs, labelled DJ-811A
which is Junior King).

Both boardsets have exactly the same fault - the colours are displayed
incorrectly.

Most of the text is blue, as are parts of some of the sprites. The
greens and reds are *extremely* faint but can just about be seen.

A better way to see what I'm on about is to look here:

http://www.brasington.org/arcade/tech/dkj/

Look at the pictures for 'Bad 2F (Prom 256x4)'.

This of course indicates that the PROM at 2F is bad, but it's not as
it works fine in another DK Jr board (different type of bootleg).
Also, a known good PROM produces the same fault. I've tried swapping
out the other colour PROMs too but to no avail. The sockets are okay.

Also checked the resistors attached to the PROMs and they're fine.

So I'm a bit puzzled.

Does this boardset need to be modified in some way in order to produce
the correct colours? It seems too coincidental that both boardsets
have *exactly* the same fault.

It's not as if the colours are inverted either.

And yes, it's wired up correctly. :)

Thanks for any help anyone can offer
Phil