[GreenKeys] Hal ST6 (again)

[Keith Densmore]

Greetings All,
A rattling ST6 showed up at the local hamfest, and of course, I bought it. I know this has been gone over before, but does anyone know a source of a manual for these online? I think I figured where the circuit boards go, but one is missing, the last board,  possibly labelled XTK. Can anyone tell me what this board does, and/or if anyone has one for sale?

Thanks,
Keith, VE3TS