Today i went down to the Dutch Commodore Users Group and took the defective SX64 and a little box stuffed with ICs with me. I met up with Erwin (E-man) and we took the bit and pieces of the SX64 apart. After replacing the PLA, screwing everything back together we still had the same condition on the SX64. The next option was to replace the 6510 CPU with an old C64 CPU as they have the same specs anyway and bingo!
What a party to see every section of the diagnostics cartridge of E-man to be completed as OK.