CDJ 900 cue button problem

Hey there!

From one moment to the next the Cue Button stopped working completely on one of my cdj 900's.

as its an older player i expected it to be the blister-switch under the cue button. my second player had a simular issue a year ago and that was easily fixed by having that part renewed.

Unfortunately the switch isnt the problem. i've measured it and it works perfectly fine.

i've updated the firmware ( after the problem occure) checked most of the common settings for anything weird but cant get any further.

Any other ideas on how to resolve the problem?

many thanks in advance