The 3.5 mm miniature jack sockets used in the A-100 system before about 2002 have been very sensitive to the diameter and shape of the jack plugs of the cables used to interconnect the modules. If you have contact problems with older modules please try the following procedure:

• Disconnect the A-100 system from mains due to safety reasons
• Remove the module from the rack and disconnect the bus cable if necessary
• Insert the jack plug into the socket causing contact problems
• Press down the hollow of the "hot" contact very carefully using a slotted screwdriver (see picture below)
• This should lead to a good contact between jack plug and jack socket
• If the result is not good enough repeat the procedure without inserted plug but pay attention that the upper contact spring does not slip below the lower one. Use the screwdriver very carefully !
• Connect the bus cable to the A-100 bus board (if removed)
• Assemble the module into the A-100 frame
• Connect the A-100 system to mains and turn the system on
• Now the contact problem should no longer occur

P.S. During 2002 a new type of jack sockets with stronger springs and so-called "curly rear contacts" is used in the A-100. The problem described does not occur for modules manufactured later than about end of 2002. B.t.w. this problem occured for all manufacturers that used these sockets (S6PC, manufacturer: Cliff/England) and not only the A-100 as sometimes claimed.