We're discussing both Y unit and T unit. It's just a different chip depending on the platform.
Ive never used MK+, when you're on battery do the unlocks stay there between boots? If yes then this will will work.
Ultimately this will allow your pcb to work exactly as it does now... Just minus...
I've not had luck getting the FM1608 working on T-Unit. it throws a write error
supposedly the STK12C68 works on T-unit according to that KLOV thread though I'm not too keen on the way they wired the cap on pin1. I wondering if that is even needed or if pin 1 on the socket could be removed...
that copy command you did should work; HOWEVER the rom files you're using need to be exactly half the size...
copy /b lower.rom+upper.rom combined.rom
an alternative command is the "type" command
type lower.rom upper.rom > combined.rom
I tend to do this one as it's a bit easier to remember...
A few months back I got a deal on a Midway Strike Force with non-working sound. More recently I had an opportunity to buy another one and THAT one ended up also having non-working sounds... same symptoms
A lot of times I've been able to revive these with simple stuff like replacing the pin...