Well this one got me going! Had to have a look at the manuals to check!
SLT is quite right LGCIU #1 fail will cause T/R #1 fail. I have had it too, as a line defect (I am an engineer). And the simple reason is that the onside LGCIU controls the reverser actuation logic.
The complicated answer is a bit more involved (aren't they always
)
Doc is I am afraid wrong. He is also right
. Let me explain
The onside Engine Interface Unit (EIU) provides actuation logic for the T/R based on Throttle Lever Angle (TLA) less than 3 degs (This info comes from the SEC's) and a/c on the ground (from the onside LGCIU) If the conditions are met then an inhibit relay is activated. This relay then allows the FADEC ECU to control the operation of the reverser itself, provided that the T/R isolation valve (hydraulic valve) is open (this valve opens when SEC's 'see' reverse commanded and a/c on ground or less than 10 foot RA)
However, the be all and end all is that a failure of a LGCIU will result in loss of the onside reverser.
Hope this helps.