Do I understand right that the cable connectors from the new Ultimate boards to the MMU socket are different from the old ones?
I thought that they are just 1:1 cables...
Yes the cables are the same as to what signal goes where, but the Candle vs Lotharek U1MB boards are different concerning the RD4 and RD5 connections. With the Candle 'black' board requiring the insertion of 180 ohm resistors inline between the A8 motherboard and the U1MB, whereas the Lotharek board has these resistors built-in.
For those that don't know, the RD4 and RD5 signals tell the system whether an inserted cartridge is either 8k or 16k by simply routing 5vdc to the MMU. And as Jon already stated, without the resistors inline this voltage can damage the CPLD inputs on the U1MB.